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How effective are DVS and similar systems? Feedback welcome!

Filed under Damp and Mould, Ventilation and Air Quality, Ventilation Solutions.

November 20th, 2008

Direct ventilation systems (such as those marketed under the brand names DVS and HRV) consist of a fan mounted in the attic which forces dry filtered air from the attic space through a system of ducts into the living areas of the house. The creates positive air pressure which forces moisture-laden air out through gaps in the building envelope.

The DVS brand has been appraised by BRANZ as offering a solution to reducing condensation and improving ventilation, in buildings where no specific building code requirements exist for mechanical ventilation. However recent research from Otago University* has cast doubts on whether these products can deliver on some of their other claims such as providing “free heat” from the roof space, especially in winter.

We are interested in feedback from anyone who has a mechanical ventilation system installed. Where do you live, what brand have you installed and what has been your experience of how it has performed? Would you recommend the product to others?

* I J Smith, B R Carson and M R Bassett. Is there free heat in the roof spaces of New Zealand houses? Mechanical ventilation systems and heat transfer .Department of Physics, University of Otago, PO Box 56, Dunedin, New Zealand


  • Jenny, May 15th, 2009 on 3:22 am

    Hi, I had an HRV system installed over 3 years ago. I do not believe it can perform as claimed. In the summer the roof temp can reach 45°C and does not cool until late at night, and then the unit is quite noisy and so I turn it off so I can sleep. In the winter the opposite is true – the roof temp rarely exceeds the house and so you cannot possibly heat anything. The whole thing is on an 8 hour cycle, so even if you turn it off it will come back on again 8 hours later. I deferred the filter change last time because I keep it turned off when I am at home but they did come and change the filter earlier this year. I spoke to them about the noise and they agreed – it was too noisy and said someone would be in contact with me re that. I am still waiting. They also suggested, if I had better insulation in the ceiling the noise would be less. What a pity they did not take that into consideration when selling me the product. I explained about the heat/cooling issue and was advised if I installed a summer kit and another fan and another computer key pad I would notice a difference. The summer kit would draw air from the “cool” southern side of the house and help cool the roof air so you could inturn cool the house. Sounds logical but I am not prepared to spend another $2500 to find out. I am not convinced . I live in Auckland and can only ever sleep for 8 hours because my HRV thing comes on and wakes me up. For my house – hot in the summer and fridge like in the winter – it is not terribly effective. Thanks

    • owen, October 5th, 2013 on 3:03 pm

      We installed HRV – 2 motors and ducting in 2009 and believe it does transfer heat from our roof cavity. We have black ashphalt shingles on ply for roof. Also above average ceiling bats and solid masonry exterior walls with full house double glazing. We often experience 5 degrees warmer inside in winter and 5 degrees cooler in summer . But only with all doors and windows closed which is fine as the HRV is circulating the air. But I would like to know if we would have got these benefits even without the HRV , such as we never get moisture inside. By biggest bug bear is the $300 to change 2 paper filters which is on a time frame system not whether the filters need it or not. My other question is I do not see the need for filters anyway as we have not had breathing problems from breathing air coming in the window which is the same air. Just take them out – it’s easy. I think the HRV helps a little in winter but might as well turn it off in summer. You need to phone HRV to do that.

  • Pam, July 1st, 2009 on 11:10 am

    I have had a DVS system installed in my own home and in a rental property. My own home is brick with batts in the ceiling and a large gas heater in the lounge, wooden windows. I had extra vents installed in the four bedrooms. I have noticed a big difference in air quality, (the house does not have good air flow) and the bedrooms are much warmer in the winter. The system is quiet- no noise at all and no draughts. It cost about $2500 a couple of years ago. Each year a new filter is needed. It costs about $50 if you change the filter yourself but the company will come and do it for you for about $150.
    The biggest changes were seen in the rental property. This is a 3 bed fribolite house built in the 1970’s, aluminum windows. It was extremely cold as the tenant does not use the installed flued gas heater. It was damp and the bedroom on the ‘not sunny side’ had mould in the wardrobe and on the ceiling. The windows ‘cried’ a lot and in the winter it was like walking into a freezer. When the DVS was installed – one vent in lounge and one in each of the bedrooms, the supplier said it would take about 4 months to dry the house out, and about three weeks for the mould to die. They were right. After three-four weeks I just cleaned the ceiling and it looked like I had just painted it. There is no mould anywhere in the house now. The tenant still does not use the heating but the house is now much warmer. I would definitely recommend a DVS. I do need to turn it down in the winter nights. I found the agent excellent and honest- he did not recommend the heating component- said the gas heater was better.
    I am interested in trying the airfoam installation, but note the energywise site does not recommend this. Any one have comments on airfoam?

    PS I live in the Manawatu

  • Barb, August 28th, 2009 on 7:49 am

    I have a DVS, installed at least 5 years ago by a previous owner. My little faith in such systems has been blown away by experiencing our small DVS myself. Even though there are only 2 vents in our 3 bedroom home it works ! In fact, it even works when it is not turned on because early this winter I had it turned off (my initial lack of faith) and our windows were a little wet each morning but when I blocked the 2 vents with towels for a couple of days because of letting off insect bombs in our attic (I mistakingly thought the fumes could come into our home through the vents) we then had pools of water on the sills off the very wet windows because of the towels blocking the vents. Just having the vents had been making a difference. Impressed, I removed the towels and turned on the DVS, leaving it on the bottom/low setting, and wow, our windows have been always dry throughout this winter. As for heat transfer, on a sunny day the system does warm up the house, (we moved here last summer and found the house too hot for comfort until autumn arrived and now I know why), but for winter days with no sun another source of heating is necessary. We live in Orewa and I now whole heartedly recommend DVS for a dryer, more comfortable home.

  • Heather Woodroofe, March 2nd, 2010 on 8:21 am

    Had a MoistureMaster system installed 2 years ago so we have now done 2 winters with the system. It did what we wanted it to – reduced the condensation to nearly nothing, put clean, fresh healthy air in to our home and our children have benefited – son went from using a preventer to nothing and has had no asthma episodes – could have grown out of it but I think the system has definitely helped. And, LOVE a dry home.
    BUT, the negatives – absolutely freezing in winter and because the installation didn’t go according to plan the fan is very very noisy – drives me spare. But, we have contacted MoistureMaster and they are going to rectify the problem – move the fan, review vents and install the inline Heater. We have worked out, based on MM literature, that we should be able to achieve an ambient temperature of 12-14 degrees in winter by having the heater running on low/med for no more than 12 hours a day. Cost should be around $30 per month. I think alot of the problem is that people think DVS, MM, HRV are Heating Systems and they are not. Eliminating condensation in NZ buildings that are not designed to eliminate condensation is there only aim. You HAVE TO have an additional heating source to get the system to run efficiently. If you don’t you will probably freeze and the condensation reduction won’t be that good. We are very nervous about the additional $750 for the heater – alot of money with two young toddlers and one income. We just hope that because we are in Auckland we won’t need additional heating once tucked up cosy in bed at night. But we are prepared to have to instal at some stage a heat pump in our main living area. Fingers crossed for a good result – certainly reviews on these systems are all over the place and there is an awful lot of misinformation and little understanding about how condensation is caused, and reduced.

    • bryn, August 1st, 2012 on 6:02 pm

      A 2kW heater,in a Moisture master for example, will use $5.28 per 12 hours of use. That’s whopping $160 per month just to get the temperature of the roof air up from about 5 degrees to about 12 degrees before it’s pumped in the hallway…. and then you still have to heat that if you want it warmer.

      But if your prepared to spend the money, all good.

  • Phil, March 7th, 2010 on 10:10 pm

    Not at all sure this is a good idea! I have heard of some cases where the in line heaters have added a LOT of money to the power bills (we are talking $100 or more per month).

    If the outcome is a house with a comfortable temperature and reduced humidity, what you will be wanting to do is to heat the existing and incoming air up to a temp that is comfortable with at the lowest cost and least hassle.

    Peg back the airflow (if possible) to a level that balances with the existing heating – you will need to watch the humidity, and keep moisture sources under control ( use extractor fans in bathroom and kitchen, vent the drier to the outside, oput kids on pots when cooking , have security stays on some windows to get a sm,all cross draught during the day, etc).

    During winter the external air has a much lower absolute humidity (cos it’s cold) so when it comes inside and is heated then it’s relative humidity is pretty low, so maybe you dont need such a high airflow from your DVS in winter.

    Get an efficient heater or woodburner to replace that heating – 7c/kWh versus 22c/kWh for an inline heater.

    You could also look at using a dehumidifiers instead of the moisture master. They heat and dehumidify. They give out more kW in heat than is used (due to the latent heat of condensation) and 98% of the other elec eventually turns into heat (apart from the hummm and flickering lights).

  • David, March 22nd, 2010 on 3:18 am

    Heather. Don’t add a heater to your MM. They suck up the power. Better to use a heater in the rrom oyur in and heat the dry air in that room. Heaters in the roof are a waste of money.
    A ventilation system is not a heater but can add heat depending on house and roof etc. I saved $700 a winter in the south island with one just from free roof heat but not everyone can do this.
    There is a new coy with an HRV clone thats much cheaper called SAYR or something like that. They said they can do an HRV filter at $80 rather than $200 and we all know the big companies make a fortune.
    There controller looks real smart. In the end airflow and price are the key.

  • Tina, April 22nd, 2010 on 7:51 am

    Wonderful comments. I have a HRV and filter needs replacing every two years, have been charged over $225.00 to replace. Where would we buy the new filter in the Auckland area?

    • Rachel, February 3rd, 2014 on 10:20 pm

      I saw some comments on here about why the HRV filters are needed. The reason they are abit more expensive then others are because they are made in Sweden. They are f8 filers which filter down to about 0.08 microns which is very very tiny. Even though you may not have breathing issues, they are still what makes our system stand out from any other. Also, the dampness we find in our home is caused by us… Humans! Cooking, showering, has heating etc. so the roof cavity is the driest part of the home, because no one showers up there! So the dry air is in a dirty part of the home, and that’s why such good filters are required. Someone was saying that they payed 300$ for there’s. They are $220 for a Janus system and $310Are you coming over for a Arizona system. Janus has one filter and Arizona has 2. You only pay for the filters. They are also only changed every TWO years so if worked out, other systems need there’s changed every year, so for a superior filter they are at a reasonable price. To the lady that wasn’t impressed with the system in summer, the summer kit is great. Just simply set your desired temp and the HRV just “knows” what to bring in. It’s not a heater or cooler but will go along side these things to make it a lot more energy efficient (as you can imagine a dryer home is a lot easier to heat then a damp one) the HRV system only runs at about 80watts which is about the same as a small light bulb, so is very cheap. It shouldn’t be turned off as it’s like resetting your phone everyday, you will loose the setting that most suits you. I recommend HRV to anyone and everyone

  • John, April 22nd, 2010 on 9:41 am

    I lived in two houses with DVS, the systems control were terrible, it would turn the fan off if the roof space became too hot but not if it was too cold. it blew cold air into the houses all day and all night. Only very occasionally did they provide warmth. I checked the quality of the air coming out of the vent on several occasions with a meter and the air contained more moisture than was in the house already. It may have made a small difference to the beading of water on the inside of the windows but that is no indication of it working as you need a temperature differential between inside and outside for the condensation to occur, the house was like a fridge when it was turned on. Ventilation is extremely important however I don’t think that DVS or HRT are very good systems although they are getting better by having heat exchangers and feeding fresh air form outside not the roof space. It amazes me that these system don’t measure humidity and rely on temperature for control and have flawed control logic.

  • David, May 3rd, 2010 on 5:01 am

    John, you must have a weird roofspace. My experience is totally the opposite although it wasn’t a DVS. I do know they have less airflow and therefore need to be on more. One comment you made is correct, the systems controller is the most important component. If it’s not clever enough, it will dribble air in when it’s able to warm and then because the house doesn’t rise in temperature fast enough you will get cold air when you don’t want it. My HRV seemed to do it correctly.
    To cover the humidity angle, they don’t need to measure it. It’s common knowledge that as air expands the moisture content stays the same which means when the roof temp rises the humidity level must be lower per cubic meter of air. Its a law of science. Thats why my experience was good, it came on when the temp rose as the controller was intelligent. But SAYR’s little touch screen one looks really good and it measures outside temperature as well it seems.

  • Andy, May 3rd, 2010 on 10:38 am

    I am surprised at some of the negativity towards PPV systems. We have had 2 now. The first was an hrv. We were very impressed with results. We moved and put in a SAYR PPVS and like the hrv, the results are amazing considering what it simply is.
    We have friends with dvs and it would appear the main difference between our SAYR and the dvs is the fan output and the ‘smart’ controller (as David said above). If you dont have a powerful enough fan and a smart enough controller then you are at a huge disadvantage and in some instances it can work against you.
    Today was a cold dank day and the sun was struggling to get through. Winter is peeking around the corner, it was 14 degrees outside and yet we had 21 deg inside, the air was dry and had fresh smell, it was mid day. It is now 10.30pm, it is 11deg outside and yet it is 20deg inside. We have used no other heating source. Our house is nothing special. It is a 1966 wooden house with no insulation in the walls and has very old batts in the ceiling.
    We will never live in another house without a PPV system.

  • Andy, May 3rd, 2010 on 9:33 pm

    Just a quick note following on from above.
    This morning at 7.30am it was 14 deg outside, a bit warmer than yesterday. It was only 15 in the ceiling and inside was 18 deg. No heating. When I left home at 8.30 it was still 14 outside. Inside was still 18 deg. Temp in the ceiling was 17.5 deg. I know by now (9.30am) the temp in the ceiling will be over the inside temp of 18 and the system will be operating at 100% and warming our home with fresh dry warmer air. We have ours set at 22deg inside so when that inside temp is reached the system will reduce down to filtering mode. It will no longer warm the house but will still introduce fresh dry air. Wow. A great system. Who would not want one. Thank you SAYR ventilation.

  • Susie, May 12th, 2010 on 3:10 am

    Tina, apparently you need to contact the appropriate HRV representative directly to purchase a new filter. There are franchises in New Lynn, Grafton, and Manukau.

  • Brian, May 12th, 2010 on 11:55 am

    Tina and Susie.

    You can get filters for HRV and DVS from a company called Filter Corp. They are about $90 and you can DIY. It is very easy to change these filters.

  • Janine, May 28th, 2010 on 2:26 am

    We have a Moisture Master with the heater included and it is amazing! Why would anyone put a system in without the heater? It will blow cold air in all winter. The heater takes the chill off and we do need a bit of extra heating to supplement it in the middle of winter, but our power bills have dramatically decreased as warm air is easier and faster to heat.. We have no roof cavity and MM were the only company who suggested we put the unit under the house with the vent outside. We approached 4 different companies and they were useless!! The salesman have no idea what they are promoting and it is false advertising. The difference is nothing short of miraculous for us and I recommend it thoroughly.

  • Matt, June 1st, 2010 on 1:18 am

    @ Barb.

    I’m glad you’re happy with your DVS system. However, I have to question your logic. The DVS (and other PPV system) is designed to work through positive pressure, forcing roof air down through the ceiling vents and pushing the internal moist air out through any available air gaps or vents.

    If you have the DVS turned off, things will actually work in reverse. Due to the passive stack effect, warmer inside air will rise, going up through the DVS ceiling vents. While this isn’t what they’re designed for, it will still provide a level of ventilation for the living areas, and I suspect this is what you experienced. If you then block off these vents, you block off this natural ventilation path, hence the increase in condensation in your home.


  • Brian, June 1st, 2010 on 9:23 am

    Janine, your braver than me to take air from under your house, especially with only a MM filter, and then pump that in whether warmed or not. I would definitely get the air tested a.s.a.p. from a recognised company who do independent tests. Your health could depend on it.

  • Jamie, June 8th, 2010 on 2:17 am

    I’m trying to weigh up which is better for my house. A ventilation system or a heat pump. Our house is an old single level 3 bedroom house with an uninsulated lean-to extention attached to the main living area. My son and I are allergy sufferers and asthmatic’s. The house is built almost directly on the clay which means no under floor insulation.

    Our house is damp and cold. There is constant condensation on the window during this time of the year. We ‘do’ have good insulation in or roof but this is comprimised by the lean-to not having any.

    Any advice would be welcome. Cheers

  • Nick, June 9th, 2010 on 2:55 am

    We live in the manawatu and had a DVS fitted into our original house (1960’s) in 2003 because our windows streamed water and we had a major mould problem in one of the bedrooms. We also had a gas fire at the time which we removed and replaced with a woodburner (because we knew that the gas fire was a major problem with condensation creation. The walls in the house actually felt wet! The DVS chap set us up with a set-up with one, yes just one outlet positioned in the hallway and due to us having it fitted at the beginning of winter he increased the money back guarantee if it didn’t sort the condensation out from 3 months to a year. You can believe this or not but the condensation was virtually gone within 3 weeks of starting the system up. The only down side from the system was the freezing cold air that gave you a serious wake up call every morning when coming out of the bedrooms!
    I need a system to go in our new house now (a pre 1900 villa) so am open to peoples suggestions on whos systems are the best.
    That is any one except HRV. – I hate pushy salesmen who try to treat me like some sort of idiot which seems to be the way they work. Plus of course anyone who thinks they can cook sausages on a roof while sitting on it in only their shorts has got to be pretty dumb

  • Nick, June 9th, 2010 on 3:11 am

    Hey Jamie,
    I’m an ex-builder and to be honest with you all three parts are as important as eachother. There is no point thowing money at a heatpump if you are going to lose a load of your heat straight out of the walls (they are not as cheap to run as the salesmen would have you believe although they are cheaper than many other forms of heating!)
    Damp air is extremely hard to warm up so if your house is damp, again it’s a waste of money to buy the heat pump.
    If money allows I would get the walls insulated at the same time as having the ventilation system put in. If not put the ventilation system in first. The most important thing to understand is that each of these three parts will not work efficiently without the others.
    Just be warned some of the salesmen/companies will tell you anything to sell you their product. Ventilation systems DO NOT HEAT except when you don’t actually need it. If they tell you it does more than helps condensation and, possibly, allergies make them prove their statement. I would be very suprised if they can (they will try to baffle you with lots of figures). If they get nervous or agitated when they have to explain it means they either don’t know or they are trying to pull a fast one.
    Hope this helps

  • Brian, June 9th, 2010 on 7:05 am


    The first thing you need to do is to decide what are the main things you are wanting to achieve.

    Do you just want to warm your home?
    Do you want a drier home, which is easier to heat.
    Do you want to reduce moisture?
    Do you want to reduce pollutants, dust, pollens?
    Is there people in the home with allergies, athsma etc?

    There are really only 2 options.

    1. Heat Pumps.

    2. PPVS – Positive Pressure Ventilation Systems.

    Lets quickly look at some pros and cons.

    1. Heat Pumps.

    pros: Very effective method to heat your home. Relatively cost effective, say basic heat pump at $2500.
    To run a 6kw heat pump will cost the same as running a 2kw fan heater.

    Cons: Does not dry or dehumidify your home in winter. They only dehumidify on cooling mode which is not ideal in winter. Even though they are an effective and efficient heater, still the cost of running a 2kw heater over a 24 hour period would still add up for a month. It is rare for a single unit to heat a whole home so you may need 2 if you don’t want the bedrooms to be 10 deg cooler than the living area in winter. Can be noisy and unsightly.

    2. PPVS

    pros: Very good method of ventilating your home. Can drastically reduce the moisture in a whole home. The air is filtered reducing pollutants, pollens, dust, allergens, bacterias. A drier home is easier to warm and stays warm longer. In winter during the day may help in heating the home using the free solar energy provided by mother nature in the roof space ( can be 25 – 30deg in the ceiling cavity on an overcast day). Average homes cost around $3k to install and cost around $5 per month to run. Is barely noticeable and whisper quiet.

    cons: cannot heat your home with the flick of a switch… but, it not a heater per se.

    There are very good FAQ to be found at Check it out.

  • Brian, June 9th, 2010 on 7:11 am

    Jamie, what area do you live in?

  • Jamie, June 16th, 2010 on 2:29 am


  • Stu, June 22nd, 2010 on 9:14 am

    Hi has anyone had an HRV system installed in a cold area do they work at night?. We had the HRV rep around last night who said the roof space would still be warm and the system would still be able to circulate air and work as it should. We live in Upper Hutt Wellington where we get down to 1 or lower some nights in winter so not sure how good HRV is in a cold climate? any suggestions or feedback would be really appreciated

  • Karyn, June 25th, 2010 on 6:21 am

    This feedback is very helpful. Has anyone had a Lossnay system installed, or any other system that draws air from outside? I already have a heat pump, but need something to reduce condensation, and warm up the bedrooms. But I’m worried about noise, and the cost.

  • Janine, June 27th, 2010 on 8:20 am

    Brian, the vent is on the outside of our house therefore it does not take air from under the house. Air quality is amazing.

  • Brian, June 27th, 2010 on 9:30 am

    Stu. An HRV, SAYR or DVS are all positive pressure ventilation systems. With out getting into the complete complexities of how they work, you have to realise they are not heaters. They are very good at reducing moisture and condensation and during the day time they contribute to heating your home with the energy from mother nature when it is available. During the evening, the better ones will automatically shut down to a fraction of their full speed. By doing this you still get the benefits of fresh filtered air but not enough to influence the temperature inside the home. If the HRV rep said that the airspace in the ceiling would still be warm at night, I suspect he either does not know what he is talking about or he is trying to deceive you. Basically around 5 or 6pm the temperature in the ceiling will be below the temp inside the house so there will not be a heating advantage. What you do have is a warmer drier home which is easier to heat and easier to keep warmer for longer. The air is clean and healthy. Dont be put off, positive pressure ventilation is a good investment.

  • Carolyn, June 28th, 2010 on 1:52 am

    I had a PPV system “including heat recovery” installed 2 years ago. The sales rep and the brochure claimed that the heat generated by my Kent fire would be transferred to the bedrooms via vents in the roof cavity. This air coming out of these vents is still very cold in winter (despite the fire roaring) and blows directly over our faces during the night. There is still condensation on my windows when the outside temperature falls below 10 degrees at night. There is no noticeable difference in warmth throughout the house during the day. In fact, it feels warmer outside today than inside the house. I think the money would have been better spent on wall and underfloor insulation. Beware of exaggerated sales claims. I am still negotiating with the company to try and get this system removed from my house, it has failed to live up to the company’s claims.

  • Nick, June 28th, 2010 on 7:38 am

    Unless your roof is sealed (which it won’t be) there is no chance of your roof being warm enough to give any benefit to you in the morning. Of course it will still be able to circulate air – that’s what it’s designed to do!
    HRV just like DVS and SAYR and a multitude of other like systems is a ventilation system NOT a heating system therefore any heat you get from it is incidental and as far as I’m concerned any company that tries to sell off the system’s ability to heat is basically lying to you. We had HRV come to us (cold called) and used a damp meter to show us how damp our house was – When I asked the rep to show me proof of the meter’s accuracy or recent callibration he couldn’t/wouldn’t. I wonder why not!
    I had a DVS in my last house and it was great at dispelling the moisture but useless as a form of heating. DVS never tried to sell it to me on the back of shady heatinig claims
    I wouldn’t touch HRV with a barge pole because they have given me no reason to trust them and many reasons to not trust them. But at the end of the day – your choice mate

    • Tony H, September 17th, 2013 on 11:17 pm

      I had an HRV system installed in my last house and have had DVS installed in my present house.Having had the experience of both forms of ventilation…NOTE!!! – Ventilation NOT heating… I can honestly say the DVS leaves the HRV for dead. The HRV people are pushy beyond belief too, and when I had a concern over fire transfer the manager just shut me down….DVS not only listened but implemented my instructions based on my concerns. The concern I had was that in my career of firefighting and fire prevention I knew that if two or more rooms were connected by a trunking or piping system , then, in the event of a fire in one room the smoke and heat would be transported through that system to other unaffected rooms in the structure. HRV said that was rubbish, but DVS agreed that it was possible, and when I asked for a shut down relay connected to a smoke alarm be installed as part of the system so that if a fire were to be detected by the smoke alarm it would trigger the relay and shut the system down…thereby preventing the system from filling a room WHERE YOU COULD BE SLEEPING with smoke….and we all know that the smoke is what kills you long before the fire does!
      Also, if you look at the HRV system, the filter is placed after the fan which draws the air out of the roof space….so dirty air passes through the fan and eventually dirty fans pack up…….the DVS filter is BEFORE the fan, so dirty air is filtered before it hits the fan….result cleaner fan unit which lasts longer! Changing a filter is a diddle but HRV spun me a tale that only they were allowed to do it on penalty of voiding the guarantee….bull….I bought a filter from FIlter Corp for $ 80 which was a lot cheaper than the $ 200 for them to fit it……DVS, not a problem and the filter is cheaper too. One last funnyossity from HRV …..When your control unit shows a little light at the bottom indicating that your filter needs changing on HRV it won.t go out when you put a new filter in , and HRV would not tell me how to cancel it…they reset it when THEY did it. Fear not, if you buy a replacement filter from FIltercorp they include reset instructions and also full fitting instructions for the filter change ….so go for it……HAPPY VENTING 🙂

  • Stu, June 29th, 2010 on 8:20 am

    Thank you for all the feedback, will look at probably DVS be a good change not having to wipe windows down every morning

  • Phil Squire, July 5th, 2010 on 10:23 pm

    Recent studies commissioned by EECA and Beacon Pathway, have shown again, that forced ventilation systems are being oversold on their benefits. The main issue I have is that these companies are selling a product and like any organization with a vested interest will be very unlikely to give an unbiased assessment of whether the product is needed or not. Reducing sources of internal moisture, heating, insulation, and natural ventilation should always be the first point of call. Beacons study of numerous homes has again shown that the basics should be assessed first, and that most NZ homes are leaky (draughty) and increasing the forced ventilation is usually not going to give an efficient result.

    There are some homes, usually newer tightly sealed homes, where forced ventilation may be the only solution to bringing down indoor humidity. But again, you need to be clear about what the issue is you are trying to address. Damp, mould and “crying windows” are a sign that the damp surface is at a temperature below the dewpoint of the air inside the house. To deal with this, one either raises the temperature of the surface (double glazing and insulation effectively does this) and increase the heating, and/or decrease the moisture content of the air. Someone who comes to your home and sells you a $2k – $3k “solution” without assessing the symptoms deserves to be shown the door. You might be better spending that on a heatpump and dehumidifier and get the result you want and be warm too!

    Anyway, buyer beware but this industry is a prime example of misleading information. They are large, sales driven, and prey on people’s awareness of symptoms rather than addressing the cause. There are cases where a ventilation system is a good option, but address the basics first.

  • Elle, July 8th, 2010 on 11:24 pm

    I want to know if I should install a DVS system in my home to reduce moisture. The home is under 10 years old. I do not expect it to heat the home. Is there any negatives?

  • Ces, July 13th, 2010 on 9:59 am

    I’ve just moved from Wanaka to Dunedin last week.
    In Wanaka we were renting a two or three year old ‘designer’ house (cheaply clad) with double-glazing and gas fire in the living area which was also shared with the kitchen. In summer it was literally so hot we had to go down to the pool to lower our core temperature; so far this winter we counted up to five layers of wool on our top halves and two on our legs so as not to freeze. It was the most gruesome (actually the only) experience of new housing I’ve ever experienced. Wet windows every morning, mould flourishing in the condensation catchments. One room so cold it was crippling even with a fin heater. No difference between the brand new double-glazed house and the bach-style 1960’s fridge I stayed in a few seasons ago. Double-glazing is a rip-off if some monkey installs it.
    Same by the sounds as these dry-air systems.
    Here in Dunedin I found this site searching to see if anyone else had to turn off their MM (Moisture Master) system due to waking up thirsty as an Aussie. Our sweet, ugly 80’s brick rental has a little note above the control switch to ask us not to turn it off. I don’t know if I should or not- boy oh boy is it effective! I have turned it off over-night the last few nights simply because I can’t bear waking every few hours with such intense thirst.
    We’ll probably go back to Melbourne but being a Kiwi I’d say without reservation that if I ever lived in another house here (lived in all the major centers and ski towns) there is no way I’d be without one of these systems. And a damn fine R.O. water purification system to remove the filthy fluoride from the tonnes of water I’d necessarily consume to stay hydrated.
    Righto. : )

  • brian, July 15th, 2010 on 10:02 am

    Good PPV’s have many benefits. The amusing aspect reading a lot of these blogs is so many of the comments are clearly made by people who do have them or have not directly experienced them.

    It is said time and time again that PPV’s are not heaters. Most people know this however a lot of the knockers sole focus is on this inaccuracy and bring it up time and time again. Sure, some desperate sales people will exaggerate this aspect but this alone does not make a PPV a bad purchase.

    A good PPV helps remove moisture and a dry a home. The benefits from a dry home are many. A good PPV filters the air making the air inside the home cleaner than outside. The air in the ceiling is not recirculated, stale, old or the like. Air in the ceiling space is actually changed and flushed out more so than what is in the home. Roof spaces are designed to breath and air freely comes and goes. Because the ceiling space is relatively undisturbed it does gather dust and cobwebs but he air is fresh. A good filter will filter the impurities, making this air purer and cleaner than is inside or outside.

    Drier air is easier to heat and stays heated for longer hence saving on heating costs.
    Drier air inhibits mould growth and decreases the reproduction of dustmites making the home healthier. Good filters filter dust pollens, allergens and bacterias from the air being introduced again helping asthma and respiratory sufferers.
    A drier home requires less maintenance, makes furnishings and furnitures last longer.
    A home with a ventilation system is more secure.
    Keeps flying insects out such as flies and mosquitoes.

    These are just some of the benefits and everyone would like to have benefits such as these and I havnt spoken about heating.

    Do PPV heat your home? who cares, i’ll have one for all the other benefits anyway.

  • brian, July 15th, 2010 on 10:10 am

    Janine. What size (kw) is the heater in your system and how long do you run it for typically for this time of the year. Since you are taking outside air and heating it, you must be using a lot of energy to heat cold winter air? Do you have vents in the floor if the unit is under the house?

  • Matt, July 19th, 2010 on 1:50 am

    Hi Brian.

    You do make good points, and I suspect you are involved with a company selling Positive Pressure Systems.

    Correct, they are not heating systems, but this aspect is often pushed (by some companies more than others) as a way to sway the buying decision. I’d recommend staying well clear of any PPV company that pushes the heating aspect.

    What’s also often glossed over is how location and building type / age can have a very big influence on which ventilation / heating combination is the best to go for. For example, Heat exchange ventilation systems really need a well sealed home with very low levels of air infiltration/leakage to work efficiently.

    On the other hand, Positive Pressure Systems such as HRV actually rely on these natural gaps for the pressurised air to escape through, so I wouldn’t advise installing them in a more modern house (i.e. one with aluminium windows) unless you also install some passive vents as oulets. Otherwise you’d still need to open windows, which really negates any security & insect-proofing benefits.

    And if you’re opening the windows anyway, you’ll most likely be getting more than enough ventilation by passive means.

  • Janine, July 26th, 2010 on 4:50 am

    Brian, it is a 2kw heater and we run it for about 4 hours a day. Our power bill has never been lower as we only supplement it with a small fin heater the odd times. We used to run a 15 fin full bore and the bills were through the roof. We have a pole house so the system is not near the ground.. It’s a win win all around and we are extremely happy with it and wish we knew about it when we bought the house 9 years ago. I know of no negatives and could not conceive putting a system in without the heater unit..

  • Janine, July 26th, 2010 on 4:51 am

    Oh, and yes we have two vents in the house…

  • Howard Dixon, July 26th, 2010 on 9:08 pm

    Wanting an unbiased opinion from anyone who has had the Vent outlet heaters added to their DVS.
    Do they improve the room temperature ?
    Do they help with condensation issues?
    What do they cost to run on a monthly basis

  • Brian, July 28th, 2010 on 2:20 am

    Hey MATT.

    Sorry I cannot agree with your comments regarding PPV in modern homes. Some of our happiest customers and most effective results are people with modern homes and even brand new homes. There are claims that new homes are air tight hence PPV will not work. There is no such thing as an airtight home. There are a multitude of places air can and will escape in new or modern homes. Sure older homes are ‘breezier’ which makes a newer home appear to be better sealed. We are yet to find an age, design or style of house that a PPV will not work effectively in. (obviously not flat roofed). There is the rare occasion where some PPV systems struggle and for what ever reason perform very poorly, these cases are limited and by far the majority of cases a good PPV will perform very well. Even a poorly performing system is still better than no system at all.

  • Brian, July 28th, 2010 on 2:27 am

    Hey Janine

    Thanks for your feedback.

    I find it very interesting as I continuously come across people who have inline heaters in their PPV and they do not use them due to the horrendous power bill so its good to hear your happy with yours.

    At 2kw x 4 hours per day at say 19cents per kwh, you would be paying approximately $47 per month (not including your fin heater). That is very good and I’m sure a lot of people would be happy with that.
    I have heard of some people paying in excess of $300 per month with inline heaters in their PPV’s but they probably got a bit carried away.

  • John, July 29th, 2010 on 4:59 am

    For us so far the SAYR system seems impresive.Is anyone really unimpressed?We live an hour south of Auckland.

  • Jo, August 2nd, 2010 on 7:00 pm

    We have had a DVS installed for condensation not heating. Have found it useless and has made the room it was supposed to take the moisture out of worse. Have been told by the cfompany we need to heat the room for it to be effective. We were not told this when we purchased and wished we had never purchased it in the beginning.

  • Janine, September 23rd, 2010 on 10:17 am

    I was initially skeptical and presumed our bills would be horrendous. They really are lower than the pre-mm bills, and to wake up to dry windows and no broncitis for the past two years.. I’m sold!!

  • editor, October 11th, 2010 on 3:34 am

    Hey Jo, you might like to give us a call at the advice centre regarding your house.

    I’d be interested to know what the construction is , eg brick or wooden cladding, tiled or metal roof. Plus we may be able to help with some suggestions to help you reduce the moisture issues in your home.

    Our telephone service is completely free, and we can call you if you are out of our toll free area if you want to email us with your contact details (preferably landline). Email

    Cheers, Sarah Free (energy advisor, Wellington HEAC)

  • Kay Richards, November 18th, 2010 on 4:46 am

    I had a HRV installed in November 2009 as I was sick of crying windows and my drapes going moldy and having to get them specially cleaned each year.

    We had installed double glazing in our bedrooms which has helped a great deal with some of the condensation we were experiencing and we also have a Metro Extreme free standing fire which heats the house great in winter.

    The HRV has been great this winter, its practically eliminated the condensation and we have not had to use the fire as much as previous years as the house temperature during the day has been increased with the use of the HRV and has been more comfortable.

    I have just contacted HRV this afternoon to inquire about their Summer Kit so we can cool the house down at night – last night at 10pm the roof space temperature was still in the high 30’s and the house temp was 25 – very uncomfortable to sleep in so the Summer Kit will bring in the cooler outside air from the southern side of our house and make the air temperature more bearable earlier.

  • scott, November 21st, 2010 on 9:03 pm

    I have been informed that hrv no longer do the summer kit which took air from outside when it is too hot as they have problems in that it did not work very effectively. They do something else but it costs a fortune.

  • William, December 2nd, 2010 on 10:47 am

    Hi, all

    I had the HRV system with 4 outlays installed in my Hamilton brick house (built in 1969) in June 2010.

    While it seemed to be that the HRV works fine for my friend’s house (which is a wood type), I regret to say that the system has totally failed for my house. It has actually made things much worse. Three things occurred after it is installed:
    1) The condensation problems are always there and the windows were crying
    heavily in the mornings, which were contrast to what the HRV sales person
    promised (99% free of it);
    2) The houses became colder this winter, even if the temperature was warmer than
    that in the previous year;
    3) The worst thing was we could feel the moisture on the wall in the mornings and
    had to wipe it out. However, it has left marks permanently on the wall all over
    the master bedroom. Only 2 parts were left without marks where a mirror
    and a photo frame sit. There are also clear signs around the HRV outlays to
    show some dirty traces on the ceilings.

    There was a TV interview on the “Target Programme of TV3” (7:30 pm,
    probably 6 weeks ago) which showed how badly the HRV system caused
    problems to the house. It was exactly what had happened to us. I have
    heard that the HRV system may be good for old wooden houses, but not for
    old brick ones. I don’t know whether or not it is true for all of them, but it is
    true for my case, so I strongly recommend people to do some research, to
    know what type of house you have, and to consult professionals (rather than
    listening to those sales persons) before having the HRV or similar system

  • Megan, January 17th, 2011 on 8:26 pm

    I’m just wondering if anyone knows much about ventilation systems in a home with clay pipe tiles on the roof. If the roof space is generally cooler, would it affect things more in a negative way inside the house? We are building soon and want to put a system in. The cladding on the house will be timber frame with half-brick and adobe finish.

  • Megan, January 18th, 2011 on 3:54 am

    Also, if you have an HRV or DVS system, do you really need to have double-glazing? I am in Northland.

  • editor, January 19th, 2011 on 1:04 am

    Hi Megan, sometimes HRV, DVS, or other positive pressure ventilation (ppv) systems dont work as well if there are tiled roofs, due to the air in the attic being less warm and dry.

    Also if you have a drainage cavity (between the wooden framing and the adobe/brick finish) that goes all the way down form the attic space to ground level, then a ppv system may not work well, because the damp air from ground level can be sucked up into the attic space and then forced into the living areas.

    If you have good insulation, reasonable heating in winter and good ventilation you may probably wont need a ppv system. Opening windows on opposite sides of the house, security stays so you can have some ventilation even when you are out, and even a ceiling fan to help distribute air are all important ways to imrove ventilation.

    The HRV or DVS wont have any impact on whether you will need double glazing or not, as they dont add to insulation and dont normally contribut much heat. As others have commented they are primarily ventilation devices.

    Although most new homes have double glazing specified, if your designer or architect can show that your house will still meet the H1 energy efficiency reqirements of the building code without double glazing then you do not have to have it.

    There are a number of methods that can be used to demonstrate compliance.

    See the link below for more information if you are interested.—energy-efficiency


    Sarah Free, energy advisor.

  • David, February 8th, 2011 on 5:01 am

    Our SAYR has been in a few months. We’ll see what winter does but there is far less moisture in the house now as the nights aren’t sticky anymore and I can sleep better (get cranky when I dont) so I guess that will translate to warmer in the winter at lower temperatures so logic tells me.
    I found talk of them on the blogs. And wow, the salesperson was really easy to deal with, more open and honest than the rest I had visit, really listened, got to the point quickly and laid it all out for us. No tricky sales stuff. That was all I needed to decide.

  • Nic, February 28th, 2011 on 6:27 am

    Hi all

    My wife (returning Kiwi) and I came over from the UK about a year ago and purchased a property in the Waikato not too far from Hamilton, the house is an old farmer’s cottage (extended in the 70’s) perched on a hillside and exposed to all the elements, especially the wind. We loved our little house but a big downer was the continual mopping up of water sitting on the window sills every morning (from May onwards) not to mention the dampness pervading the whole house. With cold clothes and bedding plus the amount of wood we were using in the rather old Kent fire (our only source of heating) this less than ideal situation made me do some research on PPV systems, specifically because I had never heard of them before, I don’t think they exist in the UK. Having no knowledge of PPVS I read and re-read articles, garnered opinions from sites such as these and also dug out gov’t supplied data on the effects of condensation on people as well as properties. Armed with this huge amount of data I must admit we deliberated long and hard over a purchase of such a system. However we did go for it in the end and had it installed in Sept 2010, well what can I say. No more condensation at all within 36 hours and none since also the house was noticeably warmer within the same time period, over the next few weeks things got better and better. It does “what it says on the tin” to paraphrase from an old ad in the UK lol! It does not heat the house per se and should not be considered as a heating system as it is not designed for that but should be utilised hand in hand with a proper heating appliance like a fire or heat pump. With Autumn looming and Winter just behind I tentatively await the outcome of the systems performance over the colder months, to date we are both am more than happy and feel it has been the best investment we could have made although I still need to add some more insulation around the place especially underfloor. I didn’t get the pushy sales-talk maybe because I approached them and they could tell I would brook no BS plus I advised I was looking at all providers of such systems not just them. It has so far worked well and I have had no problems whatsoever and would recommend if asked. I will post back during or after the winter period to update on its effectiveness in the grip of Winter. Regards to all

  • editor, March 3rd, 2011 on 3:58 am

    Thanks for this information Nic. Would be really interested to hear your experiences over winter.

    Cheers, Sarah Free (energy advisor)

  • Phil Squire, March 13th, 2011 on 9:58 pm

    In response to William’s comments on his HRV (Dec 2 2010), it could be possible the house has a double-brick cavity. This means the basement and ceiling space are connected through the cavity between the inner and outer brick walls. A mechanical ventilation system will draw damp air up from the basement and distribute it into the house – which is not a result you want!

    At the end of the day, all a mechanical ventilation system is doing is forcing air into the house. In most cases air that comes from outside is of a lower humidity than inside, and thus mixes with the humid air inside, lowering it’s overall moisture content. Much of this can be accomplished by passive ventilation (opening windows) and usual extractor fans, insulating, putting down a basement moisture barrier (polythene), and reducing moisture production inside.

    The HRV system installers should have checked for double brick, but if not they need to take out the system at their cost.

    Cheers, Phil

  • Richard, July 2nd, 2011 on 6:39 pm

    Can anyone tell me if they have had a two fan 5 vent system fitted from dvs, we have been told this is what we need rather than one fan and 4 vents?

  • Penny, August 8th, 2011 on 10:30 pm

    I have a DVS reclaim system installed in my house built 2010. I have outlets in all bedrooms + family and intakes in bathroom +ensuite + family. I have a wood burner in family room. The heat generated from the fire is not reclaimed and passed through to bedrooms. The bedrooms are cold and need to be heated – temp drops to 12c. The dvs blows 10c into rooms over night so have to shut down system which then allows cold air in through intake vents! The system does not reclaim heat. The system also has no advantage in summer as the bedrooms stay at 25c even with the air coming directly from outside.
    A waste of money. Would have been better off with a heat transfer kit and heat pump.

  • Sarah, August 17th, 2011 on 7:14 pm

    We have a DVS and it’s been great for condensation and ventilation. And you really notice after you’ve been away for a few days that the house doesn’t have that ‘closed up’ smell.
    As for the filters, I send my husband up into the roof once a year to get ours down. A quick run through the washing machine and it goes back up. You don’t really need a new one each year.

  • Greg, October 26th, 2011 on 10:10 am

    We had a SAYR system installed about 14 months ago after moving into a new house and realising after a few weeks how damp it was. We researched online; we had been phoned a number of times by people pushing the HRV system, and it just had that whole ‘hard sell’ feel to the whole thing. We found out about the SAYR system through online blogs and then eventually found their website. The rep who called out to see us was very professional – explaining how they would install the system, and the overall cost. No pressure whatsoever. We weighed up the cost versus potential benefits, and proceeded with the installation. The effects were noticeable from day one – even just drawing heat from the top roof cavity of a 2 storey house, there was a discernable improvement in air quality, and the feeling that everything was ‘damp’ was gone within a few days. The control panel is a breeze to use – it gives an immediate reading of outside temperature, inside temperature, and roof cavity temperature. Interesting, on a typical July/August morning, it might be 2 to 3 degrees outside, similar in the roof cavity, and maybe 10 or 11 degrees inside. By 10:00am (on a clear morning) it was getting up to 15-16 degrees in the roof cavity and the system is then blowing that warmer filtered air into every vent in the house. By 12:00 noon, it could be between 20 and 25 degrees in the roof cavity – the inside temperature would have risen to about 13 to 14 – but then if you feel the air coming directly from the vents, you can feel how warm it is compared to the inside air temperature. In our case, the inside temperature of the house was dramatically higher with the SAYR system operating than without it – and all for the cost of running a couple of fans! Of course it is different if you have an overcast day – it does rely on some sun to get the best effect of the warm air trapped in the roof cavity, but it really does work! Another huge bonus for us has been the cooling effects in the heat of summer. On a hot summers night, by 9:00pm, the air temperature inside in our home is often still 25 degrees plus, with the outside temperature between 18 and 23 degrees, and the roof cavity temperature about 22 degrees. By about 11pm, the outside temperature will have dropped a little, and once the roof cavity temperature drops below about 20 degrees, the cool fresh air pumping through the house is just enough to take the edge off, and helps us sleep. Its not air-conditioning; it can only affect the temperature according to whether the roof cavity is sufficiently warmer (or cooler) than the inside temperature in order to ‘balance’ the air temperature inside the house, but for us its been a fabulous investment, with no down sides. About 2 months ago, the SAYR rep called out to update the control panel to allow for multiple adjusting fan speeds to allow for temperature fluctuations in the roof cavity – another thing we love about the system – its really cutting edge technology in this field – I expected to pay for the service, but was all in the contract pricing… would do it all again without any hesitation.

  • Merv, November 16th, 2011 on 7:01 am

    It seems that it is essential that you ensure that the construction of your house is suitable for a Positive Pressure Ventalation System to deliver what you expect however, this should be the responsability of the PPVS company.
    There should be enough data out there now (10+ years worth) for these companies to have even a simple building suitabilty checklist that would save consumers alot of hardship, time and $$ …and themselves alot of embarresment and bad publicity (Target/FairGo). Why not make it part of the contract?

    ps. We’ve had a HRV system installed for 8 years and are very happy with it apart from the cost of getting the filter replaced every few years (around $200 for a 5-10 min job). It’s great to know now that we can purchase these and change these ourselves (for less than $100)… an option HRV never, but should have told us about…. grrrr

  • Donna, November 29th, 2011 on 5:57 pm

    We had our HRV system installed a few weeks ago. It seemed to make a postive difference within a couple of days and went fine for the first week and a half. It was really quiet – didn’t really notice it at all – even when in full fan mode.
    Then suddenly one day it started making a real racket when the fan kicked in and was so loud I felt for sure something had gone really wrong so turned the system off.
    Each time we turned it back on, it did the same thing.
    It took 5 days and speaking to 4 different people at hrv before we got any response/advice. In fact it was only when their insulation salesperson came to visit us that we complained again and someone phoned soon after. The response was that they would send someone out to fit a “silencer” kit. This took 10 days for someone to come and do. I didn’t want a silencer fitted – I wanted the noise stopped – it did not make the noise in the first week or so….The silencer has reduced the noise a bit but it is still there whenever the fan kicks in. The trouble is, this is right above the bedrooms. The system also does not seem to be working as effectively as it did in the beginning. Unfortunately HRV seem VERY uninterested in sorting anything out.
    Oh and by the way, don’t go for their insulation either….a whole different story!

  • Tim, February 1st, 2012 on 10:51 pm

    Hi – anyone had experience of the Cleanaire system? Appears to have true heat recovery (closed box, not via roofspace), different to most other systems in the market. While I understand fully that it’s no substitute for a heater, I was wondering if this means that some of the pitfalls of other systems (blowing cold air etc) are generally avoided, or if anyone had found other drawbacks.

  • Karen Whatarangi, February 25th, 2012 on 9:21 am

    I feel that since putting in the HRV system that my household has been sick ever since. When first put in the house smelled of stale air from the roofspace. I have a lot of children come to my house and you can guarrantee that 1 out of 3 of them will go home sick especially the ones that get asthma. Is there such a thing as bad air because of the first experience with the smell I have not installed another filter as over time the smell eased. But if it is a really hot day.even now the house smells really stale. Can anyone advise.

    • Luthos, February 29th, 2012 on 8:19 am

      I read the above comments and would like to clarify a few things. The HRV system is the only system with a Medical Grade Filter approved by the Asthma and Respritory Foundation with the Blue Butterfly Award. This means that it is approved and varified that it helps people with Asthma. I have encountered a few cases where children with Asthma needed the moisture in the air but that is very rare. In regards to noise, sometimes a silencer kit is necessary but if you turn the system off at any time, the truth is you may as well not have it running anytime. This being said, the noise is easily fixed and should be sorted out by a quick call to your local office. In regards to the air being stale, I have never come across this issue but again this is an issue you should raise with your local office.

      The most important thing I want to raise, is NO SYSTEM can always use the free heating in the roof to warm the home. Some systems have a heating coil on them that will increase the temperature but this will raise the cost of power significantly in some cases. You do need a heating source in your home during winter as most systems (DVS and HRV etc) will utilise the heat and transfer that heat around the home as well. If you buy the cheapest system you can, you will not be getting a good deal. If you only get a few vents, yes you will get benefits, something is better than nothing but you need vents in all the rooms excluding the bathroom and kitchen to achieve satisfactory ventilation. If your system gets a filter change once a year, you have to ask yourself whether it is already full before it is changed and what are you breathing while it is full?

  • david, March 12th, 2012 on 5:35 pm

    I have a SAYR. The air in my house is really nice. I went to somone elses the other day in the same neighbourhood and it was stuffy and sticky yet I had just come from mine which was cooler and drier.

    I guess varying responses here mean not all companies provide the same thing. I heard about them from a friend, and now I tell others about them too.

    I’m really happy.

  • Massimo Biscuola, April 2nd, 2012 on 6:24 pm

    If something seems too good to be true, it usually is. Ventilation systems that take dirty air out of your roof cavity and blow it into your house aren’t a good idea for the health of your family. No matter what the claimed filter performance is. The only healthy way to ventilate your house is to introduce fresh air. The other problem that these systems have is that they don’t remove stale air from your house – they just blow new air in.

    The claim that a ventilation system can heat your house by using heat from the roof cavity is also too good to be true. Your roof cavity isn’t warm when you need to heat your house – at night, in the winter or whenever it’s not sunny. If you want to heat your house, you need a heater. Worse, if you are trying to ventilate your house in the winter or at night, you are going to be blowing air that is colder than your house in.

    My company, HEATBOX, has a system that overcomes all of these problems. Our ventilation system uses an air handling unit that extracts stale air from the house and replaces it with fresh air from outside but retains the heat through a heat exchanger. We also add a super-efficient heater that heats the air entering your house through the ventilation system. It’s controlled by a 24 x 7 controller that lets you set the temperature for the time of day. If it’s already warm, the heater turns off. But the ventilation runs all the time to keep your home healthy. This system is affordable and it’s available now.

    Massimo Biscuola
    Heatbox NZ Limited

    • David Barnes, May 23rd, 2012 on 1:41 pm

      Heatbox is a heat exchanger. Why would anyone want to bring cold damp air from the outside, just filter it and then introduce that cold damp air into a house? PPV brings in warmer, drier filtered air. Heatbox can only bring in colder, damper, filtered air. Why bring that in unless that house is heated to 20 degrees 24 hours a day?… and still even then why bring in cold damp air to it? Isn’t this like the old PPV systems that introduce so much cold air at night they need a heater in the roof?

      Exactly !!!. Who ever asks this question. People need to think clearly. Using damp cold 12 degrees of air on a cold sunny day when the temp in the roof is 20 degrees and air is dry is not intelligent. Unless you had a perfectly sealed and certified eco house ( I haven’t seen one yet) a PPV system will work 10x better.

      But…. if you do have heating on 24/7 all winter ($$$$) well maybe introducing filtered, colder, damp air directly from outside will freshen it a little….

      All I ask is people do some research and think a little. Overseas where heat exchangers are built properly for extreme conditions (Canada and Europe) they only have 65-80% efficiency yet NZ companies claim 95%…. beware!

  • Paul, April 3rd, 2012 on 3:09 am

    I had a DVS system installed in my rental property in 2005 and the tenents noticed a an improvment straight away. Other tenents have complained that it blows cold air.
    I am happy with the preformance as it has lowered the condesation levels. 1960’s wooden joinery home with corrugated iron roof.
    However the last tenent broke the control panel by pushing to hard on the buttons. DVS have told me that spare parts are no longer available for my model and suggested i upgrade to a newer model at a cost of $1,900.

  • Bruce, May 17th, 2012 on 9:48 pm

    Re heat box.

    1. Roof space air comes from the outside.

    2. F7 filters filter down to .4 microns, used in general hospitals.

    3. Smart PPV systems ‘do’ help dry out damp homes making them easier to heat and stay warmer for longer. This is a fact, not just Mr Biscuolas opinion.

    Why put a heater in the roof heating cold outside air, it makes better sense to top up the inside temp which is already warmer than outside air. That is just my opinion.

    Discrediting other companies product when clearly not fully knowing or understanding the facts is not a company I would choose to deal with.

  • Gedia, May 23rd, 2012 on 1:04 pm

    To experiment buy a cheap thermometer ($2.00 shop ). Place it in the roof where the DVS will be placed, also put one in say your living room, but where you have no electrical or gas heating. Then you just need to climb into the roof 2 or 4 times a year and compare the temperatures. Just compare the temperatures from the room and the roof temp. I live in Christchurch, and at the moment the dinning room is 13 degs but coming out the DVS is 18 degs, which = 5 degs heat from the roof for nothing or just a little power for fan. My daughter had on fitted, as she had a lot of problems with condensation, and I can assure you it was a lot, after the DVS system virtually none and the house is warmer. I am that taken by them now by studying my one and my daughters that I am going to fit another one to my house as to me I have enough roof space to be able to retrieve enough heat to justify two units, but I have studied it for say 5 years by putting thermometer in my roof. It does depend on your roof some what? As my daughter has a dark grey long run iron roof, this is the best, as if you put your hand on the car of a black car, then your hand on a white car on a hot day, it is a simple experiment on how roof colors effect the heat in your roof. My roof is an orange colour, so my daughters house recovers a higher heat as her roof caverty gets hotter. And yes the university is right, about not getting heat in the winter, but their still is more days that the sun comes out, and the roof heats up quickly. Every time you get up in the roof it is imaging how hot it gets, but at night obviously no, but you turn it off , or have it on a computer on / off mode depending on the temp. I just turm my one on manually as I think I leave it on longer, as I put a thermometer siting it in the outlet at the room so I can see the temp that has come out of it. If the temp that is coming out of it is higher than the room temp I leave it on, if lower I turn it off. I fitted a DIY do it yourself Weiss, product, and are very happy. If you can do your own it saves. You a lot of money. As a DVS is only a fan and some plastic tubing, sucks the air from the roof and blows it into your room. The other simple way is to on a hot day but has to be hot just climb into the roof cavity and you will feel the difference. But I suggest you get a thermometer as then it shows the difference of even from 1. To. 30 degs Even degs difference. So I feel I have more knowledge of DVS systems than the university. You do not need to be very intelligent to know that if it is freezing outside the roof is going to be cold but most days on a frosty day the sun comes out, AND THE DAYS ARE NORMALLY BECOME VERY GOOD WARM DAYS AND THE OUTSIDE TEMP IS WARMER THAN INSIDE ! But the roof warms up every time the sun is out..
    My knowledge comes by being interested in this system and always thought that this heat in the roof was wasted, and well before they were invented put a fan in the roof to blow the heat down , but just did not manufacture it, but I should have, as every roof I have been in was always so much warmer than DOWN inside the house. I am a motor mechanic, engineering, and now do handyman work, but this DIY system interests me as it is free heat. At first I wondered if it was worth it but with always having a thermometer in roof cavity, a thermometer in some of the rooms and a thermometer at all of the ceiling outlets I can see immediately the proof of the fitting of these units.
    So to summarize this, if interested buy cheap thermometers and place where I suggest and you will see for your self, no matter what I have said the evidence is their for you to see.

  • Gordon, May 24th, 2012 on 10:40 pm

    I have just installed SAYR system and it can heat up our house when the sun is out from late morning till the early afternoon. However, the smell of the under-roof air isn’t very pleasant, as it feels stale. They told me to put the system on ‘high’ so that under-roof air would be replaced with a fresh air from outside. Yes, it worked for that day, but then it would get stale the next day. They told me it would take a few days to re-circulate the air. It’s been a week now, but no change in the smell, even though we don’t have crying windows anymore. So, the air is dry, but not fresh (yet). We do have some old insulation under roof, which may be smelly, but we hope it will be better when we put new under-roof insulation, which is planned in the next few weeks 🙂

  • jennifer, May 27th, 2012 on 10:13 pm

    I have lived in a rental property for three years now that has an hrv system installed. The system appears to remove condensation most of the time but the house gets very damp and mouldy. I have started to turn the hrv off in the evening so I can heat my house, the hrv blows cold air blows out through the system vents into the ceiling and makes the house difficult to heat. The hrv turns itself back on at some point during the night which I find very annoying. The hrv system hasn’t improved my asthma, the house seems to have the most mould nearest the system vents and the house is no warmer or easier to heat. I hate the bloody thing!

  • taran dhillon, May 30th, 2012 on 10:23 pm

    we are a ventilation company to different on level of filters we use a hepa filter h13
    99.99 % suspended air particles would be filtered out.
    we reclaim heat from the roof and if you have a fire-place we can transfer heat from that area and put it into the entire house / we can also use a heap pump to ventilate the entire house .

    free quotes

    0508 ZEPHYR (937 497)

  • Natasha, June 5th, 2012 on 5:30 pm

    Has anyone experienced mechanical ventilation systems in a Lockwood house? We don’t have a ceiling cavity and thus would have to duct from outside or under the floor. But is this effective enough to justify the cost? We have a pole house on a native bush site and have a very effective metro wood burner that heats the whole house. So our primary goal is to reduce mould and moisture.

    Has anyone experienced ‘SmartVent’ with heat recovery system? Apparently it extracts stale, moisture-laden air from inside your home and brings in fresher, drier air simultaneously.
    I quote from their website “Synergy is a completely balanced system, that recovers and re- uses up to 90% of the heat from the warm air extracted from within your home. An extremely energy efficient way to re-use heat you have already paid for. ”

    Any advice would be greatly appreciated.

  • Sam, June 6th, 2012 on 1:49 pm

    Does anyone know where i can buy an HRV ventilation duct outlet cover?
    Or one of similar size/shape?
    I have a DVS system (which I’m not that impressed with) and the new work done on our bedroom ceiling won’t allow the old DVS outlet cover to fit anymore,but I know the HRV outlet cover is much smaller.
    I have spoken to HRV but they are not interested in selling me one.

  • Rhodeo, June 13th, 2012 on 3:50 pm

    Hi, I had a sayr system installed in march so far I’ve been happy with it but over the last few weeks the condensation has been really bad. This was the main reason I got the system installed. I have two heat pumps as well so the house is lovely and warm except for one bedroom which is like an ice box 🙁 I had DVS in my old house and never had condensation. Does anyone else have this problem or is it just us? May be the system isn’t working properly?

    • Joe, August 13th, 2012 on 6:39 pm

      Hi Rhodeo,

      This year has been bad for winter high humidity, much worse than last year, that will explain why your ventilation system has not performed the same as last year. Its not the brand, its what it does, they will all be experiencing the same problems on and off this winter. Problem we have been getting a lot of warmer wetter days which is rife for high humidity. This will cause condensation when it gets very cold overnight but you will find by the following day if it has been colder during the day then the problem goes only to return the next time it is warm and wet. Just think back to before you had the system installed, bet it was much worse than what your getting now.

      Rgds Joe.

  • Steve, June 14th, 2012 on 10:16 pm

    We live in Dunedin and previously had a HRV whic certainly kept the house dry but we did find there could be a cold draught coming from the vents during the evenings. We have since moved and in a warm and fairly dry 1930s villa but contemplating putting in a system just to dry it out a little, clean the air for the kids, and hopefully reduced heating costs. The HRV salesman was way too agressive, and so considering DVS or Hometech, has anyone else experienced cold draughts coming from a DVS system? DVS reccommended a 4 vent system but we have a fairly large house and wonder if this is sufficent. For a 4 vent one fan system we were quoted $3500 which appears expensive or is this the going rate?

    Appreciate any thoughts

  • Terry, June 26th, 2012 on 7:01 pm

    We have had a G3 DVS for about the last 4-5 years and to be honest the results are pretty average. We got it solely to help with condensation as the amount of water on the windows in the mornings was pretty horrific! Bare in mind though that there are 7 of us in the house which doesn’t help things, also the other half likes to put the laundry out in the lounge to dry overnight which I know contributes to the weeping windows. Even so, when we don’t have laundry drying out the windows are still full of condensation in the mornings.

    We were orignally told to leave a gap in the curtains so that the air could circulate and this would stop the condensation happening. This did not help any at all. We have a 4 bedroom house and have one vent in our lounge and another in the hallway. As we live down the far south it is very rare for the temperature in the roof to exceed what the temperature is outside or inside the house. Generally overnight the temperature is in the single digits and the last thing I need is that cold air blowing into the house at night.

    This winter I have it operating so that it turns on at 9.00am in the morning for 4 hours and then it will turn off. This way I hope it is helping push out some of the damper air and hopefully helping to dry out the windows a little bit. At night I block up the vents as we have a radiator system operating and a heat pump down the hallway and I think all that warm air just ends up going back up through the vents into the ceiling space, a waste of energy. I have noticed since I started blocking up the vents that the rooms do reach a temperature faster and hold it for longer. I then unblock the vents in the morning so that they can do their thing. A good idea would be for DVS to add some function so that this can happen automatically when not in use or even if you could slide the vent openings to a closed position.

    All in all our experience with the DVS G3 system are as I said earlier,average. I imagine if I lived way up north where there is more heat available that this system would be of more use but down here it’s usefulness is pretty limited because of the cooler climate.

  • Dane, June 29th, 2012 on 11:36 am

    Hi all. Interesting topic

    We live in a 100yo villa in Auckland which came with an HRV when we bought the house, however this is our first Winter (it’s currently end of June). We obviously don’t know what he house was like before the HRV was installed, but it does seem to do a pretty good job. There are a few circumstances where it does provide heating – such as a sunny winter morning will heat the roof cavity a little and blow the air down into the house. But of course, no it’s not a heating system. In terms of ventilation, it’s quite a dry house. The rooms that have HRV vents in them generally don’t have any condensation on them – certainly not to the amount that you would bother wiping them down. House does have a ‘dry’ feeling to it. In terms of noise, only ever hear a bit of ‘white noise’ coming through the vents.. pretty close to silent operation.

    We are currently trying to figure out what to do for heating – we are using oil heaters and are trying an econo-panel heater in our bedroom, altho with 11foot ceilings, it doesn’t really do much.

    Insulation wise, we old compressed batts in the ceiling, and nothing underfloor. Although, today (yay!) we are getting insulation installed (R2.9 blankets in ceiling, and R1.5 underfloor), so hopefully that will make the place a bit warmer.

    As the HRV system has thermometers in the roof and house, i’ve been plotting the daily temperatures of both at about 8am each morning. Over 14 days, the temp difference is 3degrees – averaging 10 in roof and 13 in the house (chilly). Hopefully within 14 days time, we should see some difference here. I will post back results if anyone is interested.

    Back to heating, we are considering heat-pumps at the moment, although it would be nice to incorporate something into our HRV to blow warm air at the same time as ventilating.

    As above, Heatbox is mentioned – I checked out their site and it says heating component can be added to existing ventilation systems – is this true – can it be added to an existing HRV system?

    BTW, we have a 155sq house, 4 bedroom, with 5 vents – one in each room and one in kitchen/dining


  • john, July 17th, 2012 on 12:09 pm

    Does anyone know if it is possible to fully insulate the attic space (Floor and Roof between rafters) and have the output from a heat pump venting into it so the HRV system will distribute it throuhgout the house?
    We have just had an HRV system installed and the condensation has disapeared within three days, I was sceptical at first but am now very happy with the system.

  • Louise, July 18th, 2012 on 2:34 am

    I had a DVS installed about 7 years ago and hate it. It does reduce condensation but it is not fresh roof air but stale roof air that is pumped into the house. When the roof space is warm the smell is more intense and so stale I have to turn it off so I lose the heating benefit. When the smell is least the air is freezing and I have trouble heating the house. The touch screen panel failed recently and it no longer works. The condensation has returned but I am not sure if I want to fix it. I feel very much like the stale air must be unhealthy or even toxic. Salesman said it would be temporary and I was disappointed that I have had no contact or after sales service despite being promised that they wanted happy customers and would work to resolve any issues. I guess because I was unhappy they didn’t want to know.



  • Puneet, July 20th, 2012 on 11:30 am

    Hello all,

    I have a hige problem with crying windows and mould in my house in East Auckland. You can feel the instant chills when you enter the home. Without any research I called HRV guy for a quote this Monday, as they have ads on TV. Not only was he very agressive in his sales pitch, he wanted a decision on the spot. When I refused, he said “it looks like you dont have the power to make a decision in this house”. I wanted to kick him out at the same instant but regretfully, I did not. He was claiming they are the only company with F7 filter and 0.4 microns particle, German fan etc but when I did my research, I found out lots of companies are doing that. He was placing his humidity checking meter at different angles everytime, (i think to get highest values) and said “that does not matter”, whereas when I read his meter manual, it clearly states a particular angle for “correct reading”.

    From all these blogs, I have found that I am not the only one who hates thier sales pitch, and it looks like thier after sales service is not good as well. I would go for any other company now but HRV. They all do pretty much the same thing for ventillation and condensation problems.

    Can anybody please advise me if the rates for these systems would go down in spring/summer season. They are sky high right now.


  • Johnsy, August 9th, 2012 on 10:10 am


    Just jumped in to the discussion, just to state that we all should not heed those salesmen and what they advocate.

    I have a DVS installed many years ago and has benefited me. What I want to state here, is that these are just Air ventilation systems, consisting of a fan to circulate the air in the house and not heaters or coolers. They are effective in reducing the moisture content in the air in your home, but (whatever the salesperson tells you –nevermind) it will never heat or cool your home. You need other systems for that.

    Also, if you are a DIY person, good with your hands, you can buy these ventilation units from one of the hardware stores and install them yourselves. You will save loads of money doing that.

  • Bruce, August 13th, 2012 on 6:27 pm

    Once everyone gets past the heat/not heat discussions and realisesthatt the true benefits behind positive pressure ventilation is to control moisture in the home, then the better everyone will be off.

    They use a conditioning principle that affects everyhouse differently dependant on many variables. By lowering the humidity inside the home, on average, it makes the air drier and in time everything inside including the structure drier. A drier home is better than a damp home, no arguments there.

    Many different systems out there, different quality, performance, price and user interface. Anything is better than nothing, better is better.

    We have a SAYR positive pressure ventilation system in our home, its one of the better systems and it has made a big difference to our indoor air quality and moisture control.

    The systems from the hardware stores are a bit like buying from the $2 shop. You still get a product but how long will it last and will it actually do exactly what you want it to do.

  • Denise, August 15th, 2012 on 2:32 pm

    We brought our house back in Feb with an HRV already installed. I have been completely happy with the system. There has been no exessive noise or smells and the house always feels dry and cosy. Our house is an old 70’s weatherboard house and our only heating resource is a Metro fire place that pumps the heat out to the entire house. However, just this morning I had an HRV service man in to check the system because despite the system being on high we were still getting condensation on the windows on really cold days and having a few small issues with mould. I was told that the control panel being used was a 2nd generation panel (approx 9yrs old) and it would make a huge difference if we installed a new panel – cost $455, making it more efficient. Plus the filters needed changing which was another $250. I’ve done a little investigating and have found out we can buy the filters and install them ourselves ($90) but that still leaves us with a new panel to buy.
    It seems exessive amount to change an electronic panel the size of a light switch. Especially when my husband would be quite capable of installing it himself – but we HRV won’t let us do that….

  • Don, August 18th, 2012 on 8:44 am

    PPV systems work by pushing out damp air. In my humble opinion, in some houses where the joinery and doors are well sealed and there are very little gaps in the home, ie tight, there will be times the system will not work. Probably on very cold days where roof space air is cold.The moisture will only be absorbed by furnishings and carpet, only to be released later on. Possible rememdy would be to open a window slightly?
    With regarding buying from a hardware shop models, I can say that Ive seen Smartvent in a major retailer, and Heatbox, which are in my opinion, on par with the other major brands, only without the padded price.

    • Joe, November 18th, 2012 on 12:26 am

      Don, smartvent are a budget system and do not compare with the likes of HRV, SAYR or DVS but they are cheaper. Do you want a motor scooter or a motor car ? They are not fully automatic, have a low output fan, do not have a wide range of fan speed controls, diffusers are big and ugly (IMO).They have a good filter. I have heard they are also not very good for customer service when things go wrong (on the Consumer forum site). They do a job at a price but arenot equal to the above, in my opinion. Regards.

  • Roger Kelling, August 30th, 2012 on 2:19 pm

    I can believe the logic behind the heat options on these systems. Heating the air in the roof cavity is crazy. Requires much less energy in winter to heat the rooms almost without exception in all houses. With thought and in the right houses these systems work but wont work well without thought going into placement of vents and even suitablity of the house for a system. The sales tactics of agents who work for these places often means there is little or no though that goes into how suitable their product is for your house.

  • Sandy, November 23rd, 2012 on 5:25 pm

    We have just recently installed a DVS system and have noticed a huge difference, but not to the positive. Prior to getting it our house is usually cool in the summer. But, the last few days (with a high of about 21 degrees) has been extremely unbearable inside. We’ve set the system to 20 degrees but it usually goes above that! The last few days the house has been 27 degrees and the roof over 40 degrees…and it’s not even summer yet! We do not see the benefits of this system at all!

  • Ma, December 24th, 2012 on 12:05 am

    Ours wasn’t installed by a registered elestrician, damage was done to our property that was never reimbersed and the system is crap. It is never cool in the summer and hot in the winter, our house smelt like roofspace and my childrens sore tums have gone away since not using this product

  • celina Browne, December 28th, 2012 on 11:46 pm

    can someone tell me what is the name of the stuff that are used to block noise in the ceiling? They are like batts. but they are not batts. Someone is living above my flat (2 storey) and I could hear alot of noise. Also will these stuff warm up the room …

  • Grant, January 6th, 2013 on 12:24 pm

    We built a new house in the Waitakere Ranges in 2009 and it was damp and cold. I bought a dehumidifier address the dampness as the house was always damp causing windows to weep with moisture and things became mouldy. The house was well insulated but we never felt warm even with heaters running. In 2010, the HRV people cold called and presented their system and we got it installed. The place began to dry out quite quickly and I could feel the heat as I came home in the evenings after work. The temperature comes up much more quickly in the day during summer – the HRV switches off automatically when the temperature I set is reached – usually 22 deg C, although I can set it up to 24 deg C. We have not used the dehumidifier since putting in the HRV. In the winter there is not much heating from the HRV but it does just tick over with a very slight air movement and that keeps the place dry but not warm. We have a psudo tile roof in charcoal colour made from pressed steel so that absorbs heat into the roof cavity very well. The HRV has been money well spent for us and saves on winter energy costs as we don’t need to use heaters until later in the day compared with what we used to do before we got the HRV installed. We don’t hear it unless it is running full, say 16 deg in the house in the early morning and the sun hits the roof which heats up the roof cavity and automatically starts the HRV heating the house – the airflow increases through the vents and I can then hear a gentle airflow noise but it’s not disturbing and you cn feel the heat coming in. They change the filter every two years – I can’t remember the cost for filter change but it’s not very much. The air is fresh as the roof cavity does get air flow as a matter of course from outside through the tiles, roof barges etc so it’s not true to say the roof cavity has stale air as I have read in the University of Otago’s research. I would like to see how they assessed air change (or lack of it) in roof cavities of modern houses, of for that matter, older houses.

  • Tracey, January 21st, 2013 on 9:50 am

    We have a double cavity brick house and are looking at putting in a ventilation system to get rid of the condensation. HRV have given us a quote of $4900 for a positive pressure system. Smartvent have quoted $5600 for s synergy system as they say the ppv system won’t work with a double cavity house because it sucks air up from under the house, up the wall cavity into the roof cavity and that’s cold damp air that we don’t want. A builder friend has told us that the wall cavities are sealed off from the ceiling so that argument doesn’t hold water.
    We are now confused! Any thoughts about which system is best for our house would be appreciated. I am struggling to believe any sales rep now and would like to hear from an expert on home ventilation.

    • Editor, January 21st, 2013 on 10:34 am

      Hi Tracey
      depending on where you are located, I would suggest you contact one of our members to get some impartial advice about what’s best for your home. Our members are committed to providing impartial advice that best suits the needs of the household as well as the home itself. Many of our members provide this service free of charge. You will not be getting a sales rep.

      Members are listed on our members page, but you can also contact me directly if you like

    • david, January 24th, 2013 on 12:30 pm

      Give SAYR a call. Get a comparison from them

  • Rose, February 20th, 2013 on 1:44 pm

    We bought a home a few years back with a moister master. I recently noticed it needs its filter replaced but MM 0800 number says it is in allocated but their website is still running. They list a wellington service agent but his cell is also unallocated! Anyone know how I can get our MM serviced or at least the filter replaced. We don’t want to do it ourselves as have a 2.5metre stud and neither of us are very handy. Thanks for any help you can offer

    • Radu, February 25th, 2013 on 6:13 pm

      Roe, try again the website numbers, today I phoned them for a quote and they have answered, waiting now for an agent (in Auckland)

  • denis, March 6th, 2013 on 1:40 pm

    Alternative solution in my opinion.
    If you have a new house which is fairly air tight with aluminum windows and down lights. Get security stays put in, leave the windows slightly ajar. The size of the window gap depends on the temperature outside. You can also get trickle ventilation windows that will do the same thing.

    As a heat source get a centrally ducted heat pump or braemar central gas heating with zone control, that is if you can afford it. Otherwise just use a eco panel heater for the rooms.

    This setup should regulate the temperature in all your rooms at the same time circulate fresh air into the house at a flow rate you can manually control room by room.

    And to comment on all the mixed feedback on PPV and balanced pressure system. Each house has to be accessed on a case by case basis. Reading thru the post it seems there are key variables on whether a particular system will work well or not.

    I have identified the main ones to be as follows:
    House construction (Roof type/Down lights/timber or aluminum windows/single or double cavity walls /glazed or unglazed windows/ insulation/concrete or timber construction).
    Location and weather (does it rain a lot / cloudy or sunny/dry or wet winter or dry or wet summer)
    Heating type used (radiant or air flow type heating)

    That would probably explain why the feedback is mixed on all systems currently on the market. Salespeople pushing their systems without proper assessments of a house does not help either.
    End of the day you do not really need to spend any money, just open the window.

  • Cathy, April 13th, 2013 on 2:19 pm

    I have a 16 year old brick house. Heating is by night store and flued gas fire. I have recently had the windows double glazed throughout so do not have a condensation problem. Am considering a transfer system but would appreciate independent advice as to what sort would be most suitable. Neighbours have one and say it works well at keeping their house warm as well as dry.

    I live in Masterton so winters are cold and summers (at least the last one) are hot.

    • Editor, April 15th, 2013 on 9:00 am

      Hi Cathy
      Here is a link to a website with information about heating options
      Just to clarify, are you considering a heat transfer system to make the whole of your house warmer, or is it just one or two rooms? I am guessing because of the age of your home it is fully insulated, and with double glazing your windows should also be free of gaps and draughts. Do you have proper thermal curtains in all of your living spaces and bedrooms?

      Please feel free to contact me at if you would like to discuss your situation in more detail.

  • Chrissy, April 23rd, 2013 on 11:08 am

    We have just bought a 1950s ex-state house in Auckland. It does have floor and ceiling insulation (none between walls). I do find that there is condensation throughout the house when we cook, after showers and with the current damp weather we are having. I have no illusions that a ventilation system will heat up the house, but will it clear up the condensation?
    We do have an HRV salesperson coming in tonight to do his salespitch. Seems though that SAYR has more recommendations on here. What sort of prices can we expect for a system for a 3 bedroom 90m2 house?

    • Editor, April 23rd, 2013 on 1:51 pm

      You have highlighted two major causes of condensation: showers and cooking. Do you have extractor fans in the kitchen and bathrooms which expell the air outside of the house? If not, all of this moisture will be trapped/abosrbed into your home. Other causes are: unflued gas heaters (if you have one, it’s highly recommended you change to another heating source) and drying clothes inside. Do you have an issue with heating the home? You are 100% correct that an HRV system will not heat the home, nor will it act as a heat transfer system.

      What are the seals like on your doors and windows? Could be another consideration to support proper ventilation.

      Take a look at this info from EECA

  • Jill, April 26th, 2013 on 9:03 am

    We have an HRV system and while we find it very efficient we have checked our meters and find that during summer months we are paying $100 just to run the HRV with the ‘summer system’ removing hot air from the roof space during the day. The fan is running most of the day to remove the hot air and then we are blessed with cool air during the night. However, this system is not cheap to run. We still have horrendous power bills and we now have discovered why! Anyone else had this experience?

  • Stuart, May 10th, 2013 on 3:06 pm

    Are last house had DVS and it was great we had it installed in 2008 .The house was damp and cold but within 3 months it had dried out and was warm and no weeping windows. we had 1 vent in the hall and 1 in the lounge . the vent in the hall did the 3 bedrooms and barthroom but we had 2 leave the doors open a bit this was because at night in the winter the air comming in gets cold and i did not want the vent above r heads . but it still kept the windows clear of condensation . we live in Kaitaia we get lots of sun so in the winter on sunny days it would b cold outside i would walk in the house and it would b so warm . I only use the heat pump 5 r 6 times in the winter . I am going 2 have DVS fore my new house as well.

    • Kelly, May 13th, 2013 on 4:42 pm

      Hi Stuart ,can you let me know the company’s contact details. it appears DVS is really good.

  • Toby, May 16th, 2013 on 2:29 pm

    Jill, I find your claims a bit strange in regards to your power bill. The HRV fan uses no more than 95w at full speed. So if you do the math, power is about 29c per kwh so at 95w, it would take more than 10 hours to use one kwh of power (29c). So if you spent $100 on power, $100 divided by 29c (which is a 10 hour block of running the fan) equals 344.82 blocks of 10 hours (or 3,448 hours) or 143 days which is about 4.7 months. So 50ish cents a day for keeping cool and comfortable compared to what it could cost for air cooling from say a heat pump at maybe 1500kwh (that’s a pretty small heat pump and would only cool a small area, not the whole house) for the same amount of hours? About $1500. Sounds pretty cheap to me.

    In regards to HRV giving you heat, yes it can, but it is not a heater. In the winter, when you are at work during the day, when heat is available (which is a lot if you live in maybe Nelson or Whakatane), the HRV will automatically start pumping heat from your roof space to reach the temperature you have told it you want. So when you get home at maybe 5:30, instead of trying to heat your home from rock bottom of maybe 15 degrees, you only need to heat your home from maybe 19 or 20 degrees. It’s pretty simple. That is where you get your free heat, you won’t get it all the time, but it is not a heater. And, because your home will be drier, it will be easier to heat. Plus the health benefits of 95% pure, medical grade air make HRV a great investment into a lot of homes.

    HRV use a formula to ensure a minimum of 2.5 air changes per hour over the whole house. They do most of the drying of the house during the day, and then use small pulses of air at night to control condensation that does not affect temperature or comfort. Diffusers are usually placed away from seating and beds and have a certain angle to push air over the roof and down the walls first so by the time the air arrives at you, it will be at the same temperature as the air inside the room.

    I don’t work for HRV but I have a close friend who did. When sold correctly (which judging by some comments is not always done), they are by far the best system on the market. They have over 90% market share and there is around 70 other companies scrapping for the last 10 or so percent. They are in my opinion, the superior unit.

    In regards to the filters, you need to pull the unit apart to install a new filter. HRV filters should not be substituted with cheap generic filters. It’s kinda like putting cheap japanese tyres on your ferrari, it may do the job, but at a lower level and you will not get the free customer service check on your unit either.

    Just my 2c an hour worth.

  • piria martin, May 18th, 2013 on 7:01 pm

    can u turn hrv off, how do u know filter is full.

  • Nat martin, May 23rd, 2013 on 9:56 pm

    I’ve bought hrv in both my phone places and it worked wonders. Sorted the crying windows,uneven temperature in the rooms and got rid of dampness when the sun is not able to reach the back of the house. I find the house never gets too cold and is at times warmer than the outside. I recommend this to rectify dampness and to keep the full house at an even temperature.

  • Char, May 24th, 2013 on 3:57 pm


    We are looking at putting a ventilation system in. We really need help on which is the best one to help prevent condensation and mould. But also provide the healthiest air? Some of the systems out there only circulate air from the roof, some transfer the outside air and utalise this air to heat and cool the home. Is either system NOISY? If so what has been done to help eliminate the noise.

    Our home is in Auckland? Could someone recommend a great site and we will look into and provide the benefits of why they have choose that system for their home?

  • Danella, May 26th, 2013 on 7:11 pm

    Can you put these systems in a house without a “roof space” we dont have a ceiling as such but exposed beams then the roof….

  • paul cotter, May 27th, 2013 on 9:06 pm

    They seem to work better in some parts of NZ than others. They work better in new houses, not old houses. They are very expensive for the limited value you get out of them (remember you’ll be paying aroundabout $3500)

  • Derek Singleton, May 31st, 2013 on 8:18 am

    Totally Confused. Need to sort our damp problem but cant decide what or who to use. HRV were a total waste of time. Didnt turn up for the appointment then made some rubbish excuse and promise for the next day, not a peep since. SAYR gave plenty of advice but regardless of their promises were still just sales oriented and not really honest. Just rubbished all their competitors so they could renege on the “match any price” promise by saying it was an inferior system, kept pointing me to the good blogs, all of which seem to be written by themselves.
    And refused to alter their contract which is a total rip off. If you are considering them make sure you read their contract carefully as there are clauses which enable them to change the price at any time,charge for anything they want, and I mean anything including things that have nothing to do with you, and make the warranty totally invalid. Watch out!!

    • Andy, June 11th, 2013 on 4:18 pm

      Having bought a house last year, this year we decided to purchase a home ventilation system as the condensation on the windows during the winter months drove us crazy and the blinds against the windows need to replaced due to the moisture but this was not worth doing until a solution was found. Having used a dehumdifier last year which worked great but costs a lot to run and not to mention the need to remove the water that has been gathered overnight or during the day it did not make sense to stick with this idea, especially as it would need 2 or more to capture everything in the house to keep the whole place clear. So, having completed my investigation into the companies of such systems I met with a few of them to determine for myself how the system worked and the pitch they used to sell it and make my decision on the system to purchase. One of the leading brands pretty much aimed towards their superiority without really being able to provide evidence of a superior system, and not to mention the bad call received when trying to schedule an appointment. One company tried to sell what was a decent product but could not convince me the setup was better than paying slightly more for what seemed a more sensible option. However, the one company that stood out was SAYR. The salesman was excellent, spending a lot of time telling me in detail about how a system works in general, not SAYR focused which was great to hear, and then a comparison with the other suppliers without talking about superiority or trying to “rubbish” their competitors (a different experience to that which Derek above refers too) but highlighintg the comparisons and where they felt they were against other companies. The main detail was more on the system and not on the product which was nice to hear as it really helped convince me that type of system would be ideal for our needs. From all of this it shows the systems are not too different with positives and negatives for all, but the comfort factor comes in what the system does, how it is sold, and the benefits it will provide. For me the fact that the walls in the house are above the level of damp they should be and will only get worse if untreated which will cause problems with the house, and the fact I have young children who I want to keep protected from damp meant I needed a system and the cost for the system does not need to be justified when the benefits far outweigh the potential issues if left unresolved. I do not think they are expensive and the price promise from SAYR was not something that I was paticularly interested in, I wanted a system I believed in from a company I felt went the extra mile without pushing me into a sale. The price promise from SAYR is against a comparable system which is fine (as there can be a major difference depending on which system you compare with) and against a quote received which prevents people from just saying so and so told me this price. However, this does fall down when other suppliers won’t write down their best offer to get around this so price promise can be hard to receive. I was given a price by one company on paper who gave me something else verbally but would not write it down until I signed up….. this doesn’t help save money with a price promise. The company I went with was SAYR as I felt the system was the best and felt comfortable with them as a company. As a side note when informing other companies of my decision and had those who accepted it nicely understanding the decision and one that heard so much and put the phone down on me. SAYR have so far delivered everything they promised and after sales has been great. I have no problem recommending them. My decision was through personal choice based on the reasons mentioned above but appreciate that systems of other companies are comparable.

      • Derek Singleton, June 11th, 2013 on 9:32 pm

        Wow Andy, A better PR job would be hard to find. How long have you worked for them?
        Just a bit too glib, I think people will see through it. I have no doubt there system is as good as any other but their pressure sell for me was a turn off. Subtle pressure maybe but I have the emails putting down their competitors and last chance offers and refusal to modify their contract
        even though it is so blatantly a nonsense that is totally weighted in their favour in every respect.
        All I can say is read the contract carefully and if you want one of these systems get as many quotes as possible and choose who you are comfortable with.

  • Mel, June 2nd, 2013 on 8:16 am

    We have just taken possession of a house we bought 5 weeks ago & have a week till we move in, so we went there yesterday to do some painting. The ceilings are covered in mould! Very scary as when we purchased there was no visible mould ( easy to wash off ) & even 3 weeks ago when I went to measure up the small bedrooms to see what I can fit, there was no visible mould. We have been caught up in this crazy Auckland house market, we sold a year ago & have been to countless auctions to only be outbid by hundreds of thousands. We changed our suburb search & came across a place we liked. Cheap 1970s budget house, no roof cavity & fibre board ceiling tiles in some places. After the first open home a couple put a pre auction offer in & the auction was brought forward to a couple of days after first open home. We were put on the spot & the agents said the couple had got a building inspection & they seemed confident to enough to put an offer in. We went in guns blazing & got the house at the upper end of our budget so no money in the kittty to do a much needed renovation/ extension for our family of 5 …. but yay, we have a home & can do some basic cosmetics ourselves.
    My husband started to remove the poorly painted wallpaper in what will be one of the kids rooms, to only discover more mould underneath on another layer of wallpaper. I am in freak out mode after watching enough programs talking about strains of black mould & how dangerous it is for your health , especially with young children. Today my husband plans to remove the gib to see if the black mould is superficial or if it also sits behind the walls after I had a meltdown. But I have been up to the wee hours reading about mould & definitely not something he should be doing so I will be begging that we get a professional in to test ( the scary thing is my 11 year old who was helping strip the wallpaper was complaining of itchy eyes after & we put down to his allergies but reading that this is one of the symptoms of coming in contact with the spores 🙁
    At any rate I found this amazing thread. We had a moisture master in our previous new build & were very happy … Although the smells could be gross & at some point smelt like a dead rat was in our system plus the cost of putting in the new filter was criminal.
    I am keen to get a system put in this new house but no ceiling cavity & the house only has a small cavity under the house ( not like the pole house mentioned earlier in this thread that also didn’t have a roof cavity) is there anything we can do?
    I definitely get the fact that these systems don’t heat & I am keen to get a heat pump installed although our budget is tight. As there is a low pressure hot water cylinder of 135 liters ( in the tiny kitchen) one thing we really wanted to do was get gas bought to the house to get gas hot water, being budget conscious my hubby wants to get some bayonets installed instead of a heat pump as we have the gas heaters from our old place but I am not a fan of gas heating. I think it adds way more moisture not to mention there used to be odors from the gas from time to time.
    We are a family of 5 with 3 young gorgeous children. I had open heart surgery 3 years ago ( congenital heart baby) the villa we are renting now is cold & drafty & my family has never been so sick, I walk around inside with a ski jacket on! I am just worried about this new cold wet home & a bit scared about my lovely hubbies ‘she’ll be right’ outlook.
    I would be grateful for any advice!!!

  • Sal S, June 25th, 2013 on 3:18 am

    Hi There

    I bought a 4 bedroom house last year. It does not have any HRV or DVS system except for the heat pump. Now, this winter is real full of troubles. Every morning the windows are covered with the water moisture and my ensuite is as cold as. The heat pump is installed in the dining lounge but obviously, does’nt heat the whole house.

    After reading you all comments surely through experience, I do not know what to install either DVS or HRV. My house is 170sqm. I definately need some sort of ventilation soon because i can see moulds forming on the walls. This house is built in 2004 and is in Manurewa area. At the moment I have to open all the windows in the morning to get the fresh air in and the night time turn on the Dehumidifier. Seems like dehumidifier is if no use.

  • Jennie, June 27th, 2013 on 1:23 pm

    We purchased an HRV system (two fans) for our two storey concrete tiled Auckland house approx. 7 years ago. While we have had some benefits from the system, in our opinion, the benefits were significantly overstated when we purchased it.

    We still have significant condensation problems, and the noise from the fans is far greater than we were led to believe. (I turn it off at night in summer in order to get to sleep – and ironically this is the main time that it could cool).

    What really annoys me is that both fans have failed in the last year, and since it is outside the 3 year warranty, HRV want nothing to do with it. They have told me that it is not unreasonable for both fans to fail after 6 1/2 years. This seems unreasonably short for a system that is touted (and priced) as “superior”. Between the cost of fan replacement ($800 and $690) and regular filter changes (approx. $290), this system seems like a bad choice for us. We have also been offered summer kits and new controllers, but given the cost of these options, consider that this may be putting good money after bad.

    We are considering taking the HRV system out and buying a heat pump to replace it. Has anyone else had similar experiences with HRV fans?

  • John Scarr, June 28th, 2013 on 2:19 pm

    How long should a DVS system last without repairs providing it is serviced every year and the filters changed as needed?

  • Yosarian, July 2nd, 2013 on 12:59 pm

    WE have just moved out of a house that had a DVS system built in that we never used. The house was a 1950’s brick and tile and so the roof cavity was not sealed, due to the tiles. If the ceiling is not sealed then the temperature doesn’t get too high, and also isn’t dry (the main benefit of these systems)

    I had a sparkie come and have a look and he was pretty peeved that someone had sold this system into this type of house (the former owners were old) It did have a heater but it had blown out and was probably not used after the first power bill.

    WE have now moved into another home with a DVS system that seems to work a little better. Has anyone had any experience with the Tempervents add ons?

  • Nikki, July 31st, 2013 on 8:51 pm

    I have been shopping around – smart vent, hrv, dvs and tomorrow we see moisture master. All of the products seem very similar so far but I am concerned about them blowing out cold air in winter. Our roof is tiled and it doesn’t get too warm up there in winter. I was keen about getting the warmers on the vents but am worried about how much they will cost. Are they worth while?

  • Richard, August 14th, 2013 on 3:41 pm

    We have experienced both a (terrible) HRV system and a great Heathair system. Both filtered roof air before blowing through vents into the main rooms.

    The Healthair system is great. It does just what the company said it would. It reduces condensation, keeps air clean, etc. They said it might reduce heating by costs by a quarter if we were lucky but maybe not – in fact it heats well 9 months of the year (not in depths of winter) and cools in high summer. Only in the 3 months of winter do we heat a bit, the rest of the time the warm attic air does all heating. In winter the roof air is frequently warmer than house air but the difference is too small to heat the house much, but of course the fresh, filtered air is warm and dry so there is not daytime cooling. At night we heat the bedrooms (17degC) and have a timer to heat the living room for breakfast only.

    Roof heating can be achieved, especially if you have a corrugated iron roof and your gable is oriented East/West so that the roof catches the low winter sun. In summer heating is not really required but the system cools the house at night.

    I would loudly repeat several opinions voiced above about the company HRV. They put in the first system we experienced and it almost put us off the roof ventilation altogether. The installation was custom built by the company in a large house we rented. It ran several weeks in spring and autumn – we turned the power off for at least 40 of the 52 weeks per year! We either froze all winter or cooked in summer. HRV came twice and tweeked the system without improvement. That was the extent of their support. No modifications, no improvements, no removal of dud system, no money returned (would have been to landlord). In short: no good.

    We do recommend a roof ventilation system from a good company for dry, clean air. Some heating is possible from a good system in a suitable house (such as our 80 year old bugalow).

  • MikeW, August 17th, 2013 on 3:59 pm

    Lots of comments about cold air from roof space in winter without heating element installed.
    I DIY’d my own system with Mitre10 one room heat transfer unit.
    Controlled from $10 timer/ten time settings for each day.
    I’ve programed it to turn on about an hour after Sun-up and to turn off two hours later.
    Get home from work to dryer home. Temperature inside is still the same but because the ambient air is dryer, it feels warmer.
    If system fails and catches fire, I’ve probably got no insurance cover!

  • Katilena, September 17th, 2013 on 3:58 pm

    Hi there
    I have a 2 year old daughter with Cystic Fibrosis, and live in Taita Lower Hutt. I am trying to decide whether to go for HRV or DVS???

  • Marjory B, October 2nd, 2013 on 10:52 pm

    I’m looking at HRV, SAYR and Smartvent. Have a neighbour with a Mosituremaster and house is drier but it blows too much freezing air at night so she added a heater but the power cost was really high when using it. From what I’ve discovered talking to 2 of those i have seen is you want lots during the day and as little at night to be comfortable Based on Kelly, that would make sense.

  • ronnie, November 10th, 2013 on 12:02 am

    I had hrv installed on 5/13 and had been removed bcos of having lots of trouble such as wet wall, how does this happen,when night time is extremely cold and the next day is really sunny it bring down the condensation from outside to my house and make my house wall really wet and I find out my wall started to crack when too much wet steam coming from the roof,I ring and complaints many time until they decided to take the whole system away and leave you with the hole. The management are really terrible bcos they don’t come to fix the problem but try to blame your house not suitable,but at first when the sales manager come to sell you the system promised you the dry house and fresh air and not problem but after you installed your house will be like a testing sample if it not working meaning too bad for your house. It actually expensive to run and not all the house get good result and also the filter cos like crazy.they don’t fix my wall and they don’t care,also it made I’m china . do not trust the sales person as they do not have much knowledge in the system,ask around with your friend before you decided or you will end up like me

  • Noel, November 18th, 2013 on 9:56 am

    Quick question here. Is a DVS the same as a ventilator? Thanks.

  • Ray, December 2nd, 2013 on 8:00 pm


    The most important thing to consider about an HRV system is to know what you trying to achieve, as it may save concerns later. We installed an HRV about 2 years ago for the specific purpose of removing condensation from aluminium window frames in winter. Because the windows are double glazed, the panes were fine, they stayed pretty dry on a cold night, but the frames ran with condensation. The HRV fixedthe condensation immediately, and we have had none since. As the rest, I do think the HRV cools the house a little in the summer. It is noticeable, and out power bills are not huge.

  • Daran, December 11th, 2013 on 10:28 am

    I have a HRV system and I have a lot of dust coming out the vents. leaves a black ring of dust around the vent. I have had the filters changed as required. Someone suggested I need to put vents on the out side of the house to let fresh are in as everything gets trapped in the ceiling and there is no where for it to go except through the HRV.
    Has anyone else had this issue and any suggestions?

  • Kirst, January 27th, 2014 on 1:42 pm

    We live in Dunedin in a 1905 wooden house with colour steel roof. We installed an HRV system in 2009. We love it! During the winter there may not be a lot of benefit from heat coming into the house, but it dries the house out and we find the colder rooms much easier to heat. Last summer our house was re-wired and the system was not connected for about 6 weeks. It was a beautiful, hot summer but we missed our HRV dispersing fresh air.
    We have several rental properties and have installed Drivaire systems. Operates very similar to HRV, but much cheaper installation and has a ‘sock’ filter which is quick and easy to wash and replace. We didn’t know about Drivaire when we got our home system, but have found them great in rentals for reducing condensation and dampness.

  • Brian, February 10th, 2014 on 11:42 am

    Has anyone installed a HRV SummerKit?
    Is it worth it?

  • Angel, March 14th, 2014 on 10:02 pm

    Has anyone had the solar pro system fitted which uses a solar panel to heat air from the roof space and then feed it into the house? Does anyone know how it compares to moisture master? Ideally someone living in the Dunedin area so I can compare like for like. Thanks.

  • Bob, September 11th, 2014 on 9:41 am

    “consist of a fan mounted in the attic which forces dry filtered air from the attic”

    Pray do tell how this air in the “attic” all of a sudden is more “dry” that the surrounding air outside? This is pure salesman BS, it will be just as effective to leave your windows open a bit at night to allow for air to ciculate, and you will find you will get the same dry windows without having to lay out thousands of $.

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