In my new home, on the second floor, the bathroom fans goes outside and under the roof, so the output is upside down.

They installed the type of vent with a flap that, normally with gravity and perpendicular to the ground, stays shut but since they are installed upside down they stay open all the time.

I thought about a vent like we have in the kitchen's fan, a valve that opens only when air is pushed one way, but not sure if there are any off-the-shelf for bathroom fans.

We hit -20C the past few days and the cold air was pretty apparent.

Anything I can do here?

  • Are you saying that the vent blows straight down from the soffit so that the flaps hang open? i.e. the face of the vent is horizontal, not vertical? Provide a picture if you can. – FreeMan Dec 18 '20 at 21:11
  • Bathroom fans are usually shaded pole and may be pressed on blades turning the metal part that goes around the spinning part (stator & rotor) this will reverse the rotation of the fan. If that’s what you wanted to do. – Ed Beal Dec 18 '20 at 21:12
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    Bath fans have backdraft preventers on their housing outlets already. They don't really need secondary ones outside. Is your interior one operational? You should be able to pull the fan motor out of the housing and have a look. – isherwood Dec 18 '20 at 21:38

I am going to answer this even though i should probably wait for more information.

Bathroom, and dryer vent, outlet caps that exit a wall are generally attached to the exterior wall with screws, one at each corner. There may be some silicone caulking as well. They have a male crimped pipe that fits into the duct coming from the source.

You should be able to remove the screws and pull it directly out, turn 180 degrees and re-attach.

Here is YouTube video of one with a spring loaded flapper.

enter image description here

3" or 4" Round Duct Black Wall Cap w/ Damper, supplyhouse.com

  • I had that all typed up, but I think the op's fan is in the soffit, not on the wall. – FreeMan Dec 18 '20 at 21:15
  • I had not considered that because of the mention of a flapper. – Alaska Man Dec 18 '20 at 21:18
  • Those. For everything. Tired of replacing the plastic ones. If you need it for a dryer pull the screen out. – Mazura Dec 20 '20 at 2:39

You can try to find an outlet with spring-loaded flaps. (Sounds like you already have one for the kitchen vent.)

Or, extend the outlet with a 90-degree elbow. That way the end will be facing sideways, not down.

  • Bath fans are often barely functional as they are. I wouldn't introduce further obstruction with springs. – isherwood Dec 18 '20 at 21:39
  • If the fan can't open that tiny spring, now's a good time.... – Mazura Dec 20 '20 at 2:41

You could replace the soffit vent with one that has a flap to prevent air coming inside, maybe something like that. But if it's on the second floor, you'll need a tall enough ladder.

enter image description here

Or you could pull the fan out from the bathroom (or visit the attic) and check if it has a one-way flap. Maybe it has one that is jammed open by cobwebs or something, and all that's necessary is a bit of cleaning. If it doesn't have a flap, then you can add one between the fan and the exhaust pipe. I'm not sure how it's called in English, but it looks like that:

enter image description here

Make sure you pick a model that works in the orientation it'll be installed in.

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