l just installed a Panasonic bathfan for a customer and she says she feels cold air dropping down from it in extreme cold weather. Both the fan damper and roof damper are functioning, but of course both are sloppy and could let air in. I wrapped the duct with foil insulation in the cold attic. What gives? Is there a way to trap the fan duct similar to a water drain, and prevent infiltration?
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Is the air coming in through the fan or around a poorly-sealed opening where the fan is installed? (What part of the country is this?)
I had a call
about the same thing recently, Panasonic fan with cold air leaking in. I removed the diffuser, the plastic shield that's behind it, and the fan assembly (took out 7-8 quick screws and unplugged the modular wiring connector). The backdraft damper itself was not impressive, plenty of room around the edges for air to come in. I installed an inline backdraft damper at a convenient place on the outgoing duct (a "butterfly" type, about 8" long) which helped quite a bit. Another tactic would be to install a better wall cap--the models made by Seiho perform quite well. Insulating the duct itself is important in most cases but won't stop this problem, which is outside air leaking in.
I've installed a lot of Panasonic fans, and this is the first time I've looked closely at the damper. Most people like them for their low noise levels.
If your dampers are like most dampers in self contained units ... they aren't very good and could let cold air in ... which assumes there is some negative pressure somewhere else in the house. Maybe that is the real problem ... normally, you'd expect warm air to drift up/out than have cold air come in, but this will be affected by other aspects of the house. An exhaust fan is not a system independent of the rest of the house. It ultimately affects and is affected by other characteristics/systems of the house.
I installed some Panasonic inline fans and bought a separate damper like Dave is implying in his post. The damper is a butterfly damper that closes against a weatherstrip type seal .... far superior to other dampers. Very nice damper IMO. It's a separate item you buy, but is well worth it.
Yes, you could create a cold air trap of sorts ... but maybe just as easy to install a better damper ... assuming the fan has the guts to push it open (which really shouldn't be an issue, except with some of the weak fans, maybe).
The one I remedied
had the wall cap on a gable facing the prevailing wind. It was one of the cheap, plastic, three-louver deals that you see everywhere, somewhat effective but it will let some air blow in thru it. There was also probably cold air drifting down out of the ductwork as warm air moved up into it simultaneously, sort of a mini convective loop. Then there's the owner burning a woodstove, running the dryer, and occasionally the range hood.
Good point -- the OP should check the house for negative pressure.
drafty bath fan
Thanks David, today I feel no cold air, but the outside temp is mid 30's. When it was in the teens we had the wood stove going and of course the boiler in the basement was roaring away. As I have been working at making this mid 50's home tighter I guess we just had a negative pressure thingy going.