Most texts only give numbers for 'horizontal flow' through a wall, or
'vertical flow' through a floor/ceiling. When you start putting in angles,
it becomes more 'art' than 'science' :-(
Yes, if the back side is also uninsulated, there will be losses there.
Technically, 'downward' flow is a different coefficient than 'upward', but I
think the difference is down in the 'noise level' of these estimates.
And of course, if there is a small breeze of say 3-5 mph, the convection
losses will increase. For example, the film coefficient could rise to 5
BTU/hr-degF and that would make the losses on the order of 57*(5.0) = 235
BTU/hr per ft^2. This would reduce the maximum temperature you can get from
I was just pointing out that no glazing on a nice warm, still day can
actually perform as good or even slightly better than single-pane glazing.
In warm climates, in nice weather, the glazing can be unnecessary. Of
course, if it gets down to -10F and a 'howling wind', then you might want to
go with double glazing ;-)