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Posted by on December 24, 2007, 12:01 pm
On Mon, 24 Dec 2007 16:42:25 GMT, still just me
>Heat engineering question:
>
>Background: I have some insulted flex hot air ducts in my attic
>supplying heat to the second story from the ceiling. They currently
>lose a fair amount of heat, as evidenced by an ice dam problem above
>each duct location. I heat mostly by wood so the hot air runs only few
>times a day, usually twice in the morning to bring the temps up and a
>couple runs overnight when the wood stove is burning low.
>
>I know of a variety of alternative ways to deal with the dams from the
>carpentry, roof, and venting disciplines, but I had another idea that
>seemed intuitively like it might be a better choice (but maybe not,
>intuition isn't engineering :-).
>
>If I was to insulate the ducts heavily ( they currently have the thin
>built-in flex duct insulation only and sit on 6" of fiberglass )
>would this reduce the loss of heat to the attic appreciably? Or would
>it just slow the loss so that it happens over a longer time period?
Same exact thing, just stated 2 different ways.
>I'm guessing that having more insulation between the ducts and the
>zero to 10 degree air above (when the dams form) would reduce loss
>while running, but most of the time the heat in there is just
>residual... or perhaps back-feeding from the room. Would insulation
>cut the loss to the attic itself?
Seal all air leaks. Religiously. THEN add insulation.
>
>Thanks,
--
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