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Retrofitting some double glazing can make sense

Filed under Window Insulation.

January 19th, 2011

While retrofitting double glazing to all windows would be far too expensive for most, retrofitting a few carefully selected windows can make sense.

Generally speaking, the windows which have the most heat loss (and hence the best payback for double glazing) are those where the temperature difference across the glass is the most, eg lounge, dining or kitchen windows, or windows that are south facing.

Another reason to double glaze  is when there is reluctance to draw curtains because of a night-time view ( eg some lounge windows), or curtains are not practical ( eg kitchen windows or oddly shaped windows). A further reason can be that beds or seats are  very close to a cold window, and other placement options  are limited.

It is worth noting too that even with the best double glazing, lined curtains ( if practical) still help reduce heat loss further.

We recommend either customised double glazed units or magnetically attached secondary glazing (or if budget is really tight the plastic window kits are useful as a short term solution).

See comments on the posts and

for some additional discussion on this. Or if you would like impartial advice for your own situation feel free to call us on 0800 388 588 or email us.

Sarah Free, energy advisor , Wellington region


  • Double Glazing New Zealand, March 9th, 2011 on 7:45 pm

    Great Article, thanks.

    You raised a good point about heat loss on specific parts of the home. It’s also worthwhile noting the cooling benefits of double glazing on windows which get the most sun during the summer months…

  • David, July 27th, 2011 on 11:12 am

    We have had our 90 year old villa done with a company that removed the old glass and put in a sealed double glazed unit with laminated glass in it. They guarennteed it for 10 years it has made a huge difference to the mnoise and to the tempwerature inside the house.

    • Nicola, August 31st, 2011 on 12:31 pm

      Hi David
      Can you please advise what company you used for the retrofit of your villa windows?
      Many thanks

  • SP, February 3rd, 2013 on 12:43 am

    Hi Sarah,
    I have seen another posting on this forum (, regarding a secondary retro-fit double glaze (magnetic) product called Insulglaze. I have not been able to find any other reviews from people who have had it installed. Do you have any information regarding it?

    Many thanks.

  • Bob Autridge, April 2nd, 2013 on 7:32 pm

    Great product
    attrocious service have been ringing and emailing them for approximately 6 months trying to get a cat door cut in my insulglaze. Dispite many promises no contact has ever been made.
    I will not be doing the rest of the house with this product because of this lack of service

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