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Old 02-24-09, 05:20 PM   #3
Helper EcoRenovator
Join Date: Feb 2009
Location: St. Louis, MO
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Hopefully gascort can provide more info on this. See this post about the same topic except dealing with the dryer vent exhaust. But it's basically the same problem you're facing.

I do believe that high efficiency furnaces use two PVC pipes, one to draw in air and one for exhaust. This cuts the negative air pressure in the house (what most furnaces and dryers produce). That negative air pressure will cause drafts in your house. Drawing the air in through a PVC pipe would create higher pressure in your house, which might push some of the warm air out. But, if you think about it, it's better to push 70 degree air out than suck 10 or 20 degree air in (which you then have to heat).

That's my take on it anyways.
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