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Ducting a whole house fan.

Last Post 07 Jun 2010 04:44 PM by Dana1. 3 Replies.

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cad_il

New Member

Posts:32

05 Jun 2010 11:46 AM
Hello all, I just purchased a 30" (34x34 frame) whole house fan that I plan on installing in the wall of my bonus room (finished space in attic). I'm trying to come up with ideas for venting the exhaust air. Is there a such thing as 48" flex duct. Should I just build a plywood box connecting the fan to exhaust out the roof. Can I vent out to the soffit? I'm concerned with blowback from the unfinished into the finished space. So I want to exhaust directly out of the house somehow. Any ideas?

cmkavala

Veteran Member

Posts:4327
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06 Jun 2010 03:29 PM
Posted By cad_il on 05 Jun 2010 11:46 AM Hello all, I just purchased a 30" (34x34 frame) whole house fan that I plan on installing in the wall of my bonus room (finished space in attic). I'm trying to come up with ideas for venting the exhaust air. Is there a such thing as 48" flex duct. Should I just build a plywood box connecting the fan to exhaust out the roof. Can I vent out to the soffit? I'm concerned with blowback from the unfinished into the finished space. So I want to exhaust directly out of the house somehow. Any ideas? Can you just use the bonus room without direct ducting?

Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br />

cad_il

New Member

Posts:32

06 Jun 2010 10:57 PM
That is a good idea. It would solve the blowback issue. Would still have to duct the fan into finished wall of bonus room, or the fan would be in finished floor. I like this idea though, because it makes better use of the cfm by blowing into square footage, and out the windows.

Dana1

Senior Member

Posts:6991

07 Jun 2010 04:44 PM
To work effectively, fans need less impedance than most attic ventilation schemes will provide. With your approach you end up pressurizing the attic, but the flow is limited. But if you have windows to open up the exit-impedens is low enough, but you'd still have flow issues from rooms at the end of ducts. In a ducted system a squirrel-cage type blower (as in an air-handler) will move far more air per watt (and it'll be quieter too.)