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My bathroom is on the first floor with a finished bedroom directly above and an unfinished basement directly below. It would appear to be easier to install a wall or floor fan and direct exhaust down and then out through basement wall (just above ground). I have read that moist air naturally rises so it is easier to vent up. However, are their any products to vent down?

The bathroom does have 2 external walls so it might also be possible to vent directly out through the wall. What are the drawbacks to that? How is that insulated?

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Are the 2 exterior walls parallel to each other, or perpendicular? – Tester101 May 14 '14 at 10:05
Perpendicular...1 wall has a window. – Burntforest May 14 '14 at 12:36
up vote 2 down vote accepted

Probably the best solution in your case it to directly vent out. Since you have two external walls one of the walls will allow you to vent out of it. You need to pick the one that runs perpendicular to your joists.

There is not much downside in venting out. It is easier. By venting up you are actually causing an opening in your house for hot air to escape - hot air rises, will push open vent cover, and release. With a side vent you don't have those issues. The only issue is directing the moisture away from your house but this depends on the type of exterior you have.

You will pick a place for your fan - by the shower, in-between two joists. You will point fan vent towards wall that you can vent out of. You will run duct from fan to wall. Cut hole in wall slight bigger than duct (usually 4-6" in the US). You will cap it from the outside with a vent and secure vent to outside wall. Spray foam the openings/cracks created. That part of your fan install is done. Still need to get electric up to it.

To cover your other points. You can vent out the basement but you should not have a fan anywhere other than a ceiling. Anything higher than your fan will get condensation and could eventually mold.

Edit: Forgot to mention. Give your duct work a tiny tiny slope down so any moisture will drip out instead of back to your bathroom.

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