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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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  1.  
    I'm trying to work out whether it's worth replacing some old double-glazed units, in some existing PVC windows.

    Some of them are blown and I'll replace them for appearance's sake; the question is whether replacing the others might be worthwhile.

    All I know about the existing windows is:
    - The DG units are 24mm thick, I assume 4+16+4
    - They are in a property that was initially renovated in 1979. That seems a little early for PVC windows though (?) so I'm guessing they were installed later than that.
    - A couple of the units were already blown about 8 years ago. Going on a life expectancy of 20-30 yrs for a DG unit, would suggest they were probably installed during the 90s.
    - There are no markings on the glass or the (metal) spacers that give a clue to age or spec.

    I realise that replacing the units is not going to pay for itself in terms of energy saved. This is more a judgement about whether it'll make a significant difference to comfort. The windows are in a wall that has been quite heavily insulated, and in the winter, the temperature drop near to the windows compared to the rest of the space is quite noticeable.

    A little bit of reading around suggests that the existing glazing could be as bad as 2.5 and replacement units could be as good as 1.1 ... does that sound broadly correct? Of course, it all gets complicated once you are looking at warm edge spacers and different pane sizes, and so on. And then there are the frames.
    • CommentAuthorGarethC
    • CommentTimeSep 9th 2019
     
    Or even 2.9 worst case. I suspect you have it right. No chance makes sense financially, but will reduce the cold spot significantly if you upgrade.
    • CommentAuthorlineweight
    • CommentTimeSep 9th 2019 edited
     
    This calculator (if the U values given can be trusted) is quite handy to get an idea of the effect of changing various elements of the spec.

    https://www.glasstops.co.uk/order-online/sealed-unit-rectangle.php

    For my unit thickness, worst case scenario gives 2.7 and best case 1.2.

    Changing from argon to air fill drops from 1.2 to 1.4.

    Swapping non-low-e for low-e glass makes the biggest difference though - 2.6 vs 1.2.

    So the most significant question is whether my existing windows have any kind of low-e coating or not.

    Quantifying the effect of warm-edge spacers (existing units don't have them) is a bit trickier.
    • CommentAuthorgyrogear
    • CommentTimeSep 9th 2019 edited
     
    Do you have heavy curtains across that window ?

    with a reflective inner liner...

    They sure make a big difference in my house...

    ===
    Posted By: lineweightSo the most significant question is whether my existing windows have any kind of low-e coating or not.


    you can check that in 3 seconds, using a match or a lighter held to the glass !

    gg
  2.  
    Posted By: gyrogearDo you have heavy curtains across that window ?

    with a reflective inner liner...

    They sure make a big difference in my house...

    ===
    Posted By: lineweightSo the most significant question is whether my existing windows have any kind of low-e coating or not.


    you can check that in 3 seconds, using a match or a lighter held to the glass !

    gg


    Yes I've just discovered the lighter test ... the results of which suggest there is no low-e coating (I can't see any significant difference in the flame reflection colours - whereas I can when I try it on a more recently installed 3G window installed elsewhere in the house).

    There aren't curtains on the windows, for various reasons. But the coldness is felt in the daytime too, when I'd not want curtains drawn.
    • CommentAuthorgyrogear
    • CommentTimeSep 9th 2019 edited
     
    I installed a very low-cost Uw 2.6 unit on my garage-to-workshop conversion a month ago to make a solar furnace, and am highly impressed with it so far. Dimensions 2.4 x 2 m, two sliding leaves; for 390 Euros delivered = £350 .

    I fitted it with my self & son.

    It is 4-16-4 with black composite warmedge spacer. The Low-E is on plane 3, could not axe for more !

    gg
  3.  
    Posted By: gyrogearI installed a very low-cost Uw 2.6 unit on my garage-to-workshop conversion a month ago to make a solar furnace, and am highly impressed with it so far. Dimensions 2.4 x 2 m, two sliding leaves; for 390 Euros delivered = £350 .

    I fitted it with my self & son.

    It is 4-16-4 with black composite warmedge spacer. The Low-E is on plane 3, could not axe for more !

    gg


    Did you mean to write 2.6?

    Surely it should do better than that with a low-e coating?
    • CommentAuthorgyrogear
    • CommentTimeSep 9th 2019
     
    I agree with you ! But the technical datasheet says "Uw = 2.6" so I guessed that it could be wrong. However, it has an aluminium frame, so perhaps not...

    In any case, the warranty is for 2 yrs, under CE label.

    The seals look really good but the keylock is probably rubbish quality.

    I suspect the story is, is that they are seconds for some reason or another, but it is not really an issue for me.
    It is just so much better to have daylight in "my office" now !

    The purpose of my message was, look around, you might find some low-cost bargains !

    Cheers,

    gg
  4.  
    Sorry - my mistake actually - I'd taken the 2.6 as a Ug value but wasn't paying attention and see it's the Uw value. Which could indeed be a result of the alu frames.

    Certainly seems a good price for something of that size though.
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