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I have a bathroom on the first floor of a two-floor house where the popcorn ceiling has dilated and cracked open twice within a year, and some mold is always coming back next to the ceiling, so I need to install a fan there. That bathroom has heating in the ceiling (therefore I'm avoiding ceiling fans), so I want to make a hole on the upper part of one of its walls -- one that's shared with a closet located inside the bathroom -- and install a fan there to direct the air downwards with a duct through the basement, where it would be exiting near the dryer vent with the necessary ending to avoid condensation and being a way in for animals. Does that seem like a good plan?

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Can you not shoot straight out the exterior wall? Might save a lot of effort/money in duct work. – DA01 May 13 '13 at 2:07

Most wall mount ventilation fans are intended to go thru an exterior wall to a cap.

Your plan will work, if you make allowances to support the duct away from the wall a bit, to make the initial turn down. Use smooth duct and metal tape for sealing duct sections. update Be sure to slope all horizontal runs of the duct such that they will drain any condensation to the outside.

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If the basement is an unconditioned space (no heat or A/C) I would insulate the pipe to avoid condensation forming in the vent when it enters the cooler basement. – mikes May 12 '13 at 13:26
I agree on insulating for unconditioned, but even heated basements are cooler and might cause condensation. Be sure to slope any horizontal duct to promote drainage to outside. – HerrBag May 12 '13 at 14:52
Thanks for the responses. Shooting straight through the external wall has two problems: there's no electric outlet close, from where I would get the power for the fan; and I'm not comfortable with cutting a whole in an external wall -- I never did this and it will involve insulation issues, cutting the vinyl siding and an aesthetic eyesore. – user12970 May 18 '13 at 15:34

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