Best airgap for horizontally mounted glazing?
Nirakaro
| Posted in Energy Efficiency and Durability on
I’m replacing a large skylight that is presently glazed with 25mm multiwall polycarbonate. To minimise heat loss, I want to reglaze with two sheets of the same 25mm stuff, and wonder what is the best airgap between them? I know that horizontally mounted units behave differently than vertically mounted, and I’m thinking that a small gap will minimise convection currents. So, what counts, in this context, as a small gap?
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Replies
I'm not the expert who should be responding to this but hopefully my response will kickstart some answers from others.
As far as the size of the air gap, anything 3/4" or less would be good. Over 1" and you'd start to lose effectiveness.
That said, your approach appears to me to have a "fatal flaw". The gap between 2 panes of glass in a normal double pane window is sealed airtight and the air in the gap is either replaced with an inert gas or is extremely dry. That's why, when a window seal fails you get condensation inside the gap. Your gap will almost certainly not be perfectly sealed and you will very likely get condensation in there. Unless you have access to some kind of special tools we "normal folks" don't have access to, you probably can't make the seal that you'd need between the two sheets of poly.
I think the solution might be to use polycarbonate that has as many walls built in as possible. I know I've seen it with as many as 5 walls. One sheet like that would be a more reliable way to improve the efficiency.
I hope I got this right and I hope it's useful.