dg window space

[Richard Knight]

What is better from a keeping the warmth in perspective - a gap of 16, 20 or 24mm? i.e. 4-16-4, etc....? Based on price I assume the 24 as it's certainly the most expensive. So too, in reality, what's the difference here if it can be quantified? e.g. a 20mm gap loses 25% less heat that a 16mm with a 16mm losing x amount per hour/day whatever???

Thanks,
Richard

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moderator

please note 17 & 20 which are here

your post has been split

 

[biffvernon]

It's not quite so simple. With a large gap convection takes place within the space, the circulating gas tranferring heat from the warm side to the cold. This doesn't happen much in a 16mm space but at 20mm or more the insulation value actually goes down. If warmth is your priorit then 16mm is ideal. Make sure the manufacturer is using insulated space bars - the old aluminium spacers allow heat to leak out at the edges.
On the other hand, sound insulation improves with increasing gap so if keeping the traffic noise out is your priority it might be worth choosing the larger gap. For sound insulation you get even better performance with laminated glass. Or secondary glazing.

 

[TexMex]

If you're a responsible citizen you should check that the glass has been produced from renewable resources. If it has a Kite mark, it may have been made with sand from one of our British beaches. Our coastline may get erroded even further if you buy this stuff. Your responsibility doesn't end there.

Make sure that the glass has been produced in an environmentally responsible manner. You should visit the factory and take samples from their chimneys, and the main drain, downstream of the factory. Check the faces of the workers. Do they look happy? If you find any heavy metals in your samples, or you suspect that the workers human rights are being abused, take your business elsewhere.

 

[Richard Knight]

Interesting - I'd assumed that a bigger gap meant better! Certainly here (France) the oak range from a big DIY and trade supplier is only available in 24 whereas their budget range is 20. Another supplier at the really budget end of the market is 4-16-4.

For us the key is preventing heat loss in winter, particularly in light of a new central heating system going in! Summer doesn't bother us as we tend to close those shutters which are south facing anyhow. We live in a very quiet area hence noise isn't a problem.

In light of what you say it seems the really budget range may be best for us. My bank balance will be pleased.

What difference does Argon gas make to the equation? i.e. The really budget range doesn't have it but is half the price as as range in 20mm which does.

 

[biffvernon]

Argon fill reduces the U-value by a little, maybe 0.2, so is worth having if it doesn't cost any more. There are doubts as to whether the argon will diffuse out over the years. A bigger advantage is gained by using low-emisivity glass. This can reduce U-value by between 0.5 and 1.0 depending on the type. 'Soft coat' works better than 'Hard coat' but has other disadvantages.
To comply with English Building Regulations Part L one would normally need 4-16-4mm argon fill low-e and insulated spacers to be sure of a U-value below 2.0

Thank you, TexMex, for your timely advice. I'm popping into my local Pilkington float glass factory and will ask them to turn the gas down on their furnaces. They already have a 'fuel cost surchage' on their wholesale prices. Just passing the cost of environmental destruction to the customer is clearly not enough.

 

[Richard Knight]

Biff - thank you very much for your help and truly useful input. I now have a better understanding of what's going on.... time to see if my understanding matches the French suppliers!

Much appreciated.

Richard

 

[biffvernon]

In England most of the low-e glass is Pilkington K, which is hard coated, but I believe that in France you are more likely to find soft coat made by St Gobain. Better U-value but more tricky to handle during sealed unit manufacture. Let us know what you find.