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re: payback on duct insullation
26 dec 2005
edwin pawlowski errs again:
>> according to sherwindu :
>>> i am in the process of wrapping the forced air heating ducts in my crawl
>>> space with a material that looks like bubblewrap with foil on both sides.
>>> does anyone have any idea of how much savings this will be on my gas bill?
>>> the insullation is rated at r6, but i cannot relate this to actual savings
>>> in energy.
>
>take the square foot surface of the duct, divide by r6...
... 70 ft^2 of r1 duct might lose (130-50)70ft^2/r1 = 5.6k btu/h to a 50 f
crawl space.
>multiply by the ambient temperature, add the relative humidity and that
>is the percentage of your gas bill you save.
wrapping the duct would save 70ft^2/r6x50f+50%rh = 633% of the gas bill? :-)
wrapping the duct would reduce the heat loss to (130-50)70ft^2/r7 = 800 btu/h.
then again, with an airtight crawlspace above a vapor barrier, a lot of this
heat could end up in the house. maybe it's better to insulate the crawlspace.
nick
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