Exhaust Fan


Old 08-30-03, 07:57 AM
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Exhaust Fan

I'm getting a strong backdraft through the exhaust fans in my second floor laundry room and bathroom. The exhaust fans connect to PVC pipe which go through the roof on the north side of the house. The house was new construction, and my builder says this backdraft is normal. During last winter these rooms would get very cold whenever it was windy. What can I do to fix this problem?
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Old 08-30-03, 08:14 AM
Doug Aleshire's Avatar
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I'm no expert on connecting an exhaust fan to a pvc pipe but when you properly install a bathroom exhaust fan, you have 2 things working for you.

First there is a damper on the exhaust fan unit which prevent minimum backdraft.

Second is the roof/soffit/wall vent to the exterior that the exhaust fan should be connected to. This also has a damper which in most cases prevents additional backdraft.

A pvc pipe is not the way to connect this exhaust fan for venting unless a u-bend was install ed and depending on the size of the pvc pipe that is being used. An alternative and depending on location is to install a solenoid operated damper when the fan is not in use so it closes and prevents the cold air from coming in.

The cold air, since the pvc pipe doesn't have a upside down u-bend outside, is allowing the cold air to drop like a rock and with any wind, you are getting the results you don't like.

Maybe talk to the builder again or better yet the building inspector. I feel that someone is giving you a line and half!

I have copied this post and placed it in the Repair Forum - Heating and Cooling topic. I'm sure that some additional feedback will help in this matter.

Let us know how it is going!
Old 08-30-03, 08:37 AM
Ed Imeduc's Avatar
Join Date: Aug 2002
Location: Mountain Williams Missouri
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Im with Doug here. Why dont the dampers close in the fans????????

On the vent pipe out the roof for the vents should have a damper in it.
Then lost ---why do you have a vent fan in the laundry? when you run the drier it will try and pull air back in from this fan.
You can take the fans out from inside and see if the dampers work on them or if they have dampers in them, they should.

One more if------ do you have a fireplace in this home?
New home could be tight do you use kitchen vent fan a lot and does it vent outside also? ED

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