Attic exhaust fan help- placement & load

Old 04-11-17, 03:24 PM
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Attic exhaust fan help- placement & load

I calculated attic space to be 716 square ft from 38' l x 24' w minus 2 cathedral ceilinged areas in 2nd story. House has recent roof with Cobra vent and soffits all around but has no air flow. There is a small gable vent over a bay window on front of north side of house almost at the extreme east side of house. Gable vent is directly opposite a 14' x 12' insulated cathedral space and has the other cathedral space next to it, meaning it is between the exterior wall and cathedral space. I was told by roofer to put attic fan at the other exterior wall on the west side of house and that it would be fed cool air from the soffits. Since the gable vent is sort of hemmed in and separated off in the front by the supports for the bay window I don't see how the attic fan is going to get enough air and will "steal" cooler air from the non-air conditioned house. I don't know whether it makes sense to put the attic fan there and what to get (roofer says GAF but I don't think they have the product that would work). Any ideas welcome, I am obviously not a skilled DIY person & I'm desperate to get this right. Thanks in advance. Sorry no diagram, I did a whole diagram in Google docs but it won't upload
Old 04-11-17, 04:40 PM
Join Date: Oct 2008
Location: New England
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Hi mck and welcome to the forum,
I think it takes a few posts before it will allow you to post that diagram, a spam prevention requirement.

You say the current attic is experiencing NO air flow??
If all vents are open and not blocked with insulation or other then there is air flow but natural air flow is not intended to cool an attic space. Attic ventilation is needed to remove any moisture that makes its way into that space.

Attics do get hot, but the defense against that heat is insulation. You are correct that installing an attic exhaust fan will draw air from your house and more so if the ceiling to attic hasn't been carefully air sealed.

It doesn't matter where you install the fan (the smaller the better) as the fan simply depressurizes the attic and pressure changes are shared through the attic instantly. As the pressure drops the cooler outside air will push in ALL soffit vents even when they are on the opposite side of the attic. If you address the air sealing between house and attic the penalty for operating that fan is reduced. In some homes there are large openings around plumbing vents, recessed lights, chimneys, and hidden above drop ceilings. I have links to help guide you if you go that direction.

NY is not the hottest location and you can benefit from lots of insulation in the winter as well.


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