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worms
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The Pilkington Spacia stuff looks pretty good in this recent assessment by Historic Scotland.
88v8
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Interesting. Been in touch with Histoglass, as they offer various non-float-glass options - I see their 'Crown' was used here - but alas no leaded lights so no use to me. I would not under any circumstances fit float glass, yuk.
What really surprises me about this study is the deterioration in performance over such a short time scale. It doesn't mention what putty was used, but the problems of sealed units being attacked by standard linseed putty have been known for years and Histoglass have their own special putty system; surely the installers couldn't have been that stupid, could they??
Anyway, if they deteriorate that fast, you can forget about any 'economy', as the cost of replacement (&repainting) will far far outweigh any supposed saving in heat.
Ivor
What really surprises me about this study is the deterioration in performance over such a short time scale. It doesn't mention what putty was used, but the problems of sealed units being attacked by standard linseed putty have been known for years and Histoglass have their own special putty system; surely the installers couldn't have been that stupid, could they??
Anyway, if they deteriorate that fast, you can forget about any 'economy', as the cost of replacement (&repainting) will far far outweigh any supposed saving in heat.
Ivor
88v8
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Joiner said:
The missing word is 'yet'.
Ivor
worms
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It's interesting how much lower the U-value for the vacuum unit seems to be, coming in at a U-value of 1.0 compared to the 2.0 to 2.9 for the others.
But it gladdens my heart that in another report, they found that secondary glazing using magentised acrylic sheet achieved a U value of 2.4 which seems to be comparable with most of the conventional sealed-unit double glazing options.
But it gladdens my heart that in another report, they found that secondary glazing using magentised acrylic sheet achieved a U value of 2.4 which seems to be comparable with most of the conventional sealed-unit double glazing options.
88v8
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worms said:
Yes. And jolly surprising, given that the air gap betwixt inner and outer pane on a double-hung sash is more than enough to allow interstitial convection currents. I believe the optimal gap is less than an inch, on the window illustrated I would have thought nearer 4". But it still works.
Worth persisting with my secondary DG then.
And I may say that one reason it works is that the window is draughty enough to ventilate the interstitial cavity, which as a poster on here pointed out, is essential to prevent internal condensation. That was a very valuable insight, without which my secondary DG would be now be a home fit for a family of newts.
Ivor