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Old 02-06-12, 07:34 PM   #19
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Originally Posted by NeilBlanchard View Post
It is the trapped air that provides the insulation, and I've heard that the biggest space that works is about 5/8-3/4". Less than this provides less insulation, and more than this doesn't provide more insulation because the air starts to circulate because of the thermal flow.

So you can't just put double or triple layers of glass into the muntins that are designed for single panes. If you can fit 2 layers in, then great, but the air space is probably less than optimal.
The graph I saw showed a peak insulation value at about 3/4 inch gap, but the drop off for narrower and larger gaps was quite gradual all the way out 3 inches. I'll see if I can find it again.

I guess I don't see why you can't put multiple transparent layers in spaced at a half inch to a couple inches not get an R value increment for each layer -- its the same thing that commercial triple pane windows do?

Edit: The Passive Solar Energy Book, Mazria pg 365 gives R1.01 for both 3/4 inch and 4 inch air gaps. shows
" 1/2" to 4" approximately 1.00 "

Could not find the graphs I saw before.


Last edited by GaryGary; 02-06-12 at 07:49 PM.. Reason: Added refs for R value vs gap thickness
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