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Home Repair Bathrooms DIY

bathroom fan venting

3 years ago

I want to install the fan in the ceiling and I have access to the attic. 2nd floor bathroom has no exhaust fan and desperately needs one. After looking at many ways to try and install a fan, I came up with this idea.

I want to install the fan in the ceiling and I have access to the attic which has a vent on the side of the house. The vent is fairly large and i was thinking about retrofitting a fan to the lower half with my exhaust fan duct and proper cover (kinda like a dryer vent with the flapper) and the top half with a grill similar to what is already there. Can anyone tell me what the downside of this would be?

vent on house is similar to the one in the picture. and maybe about 10 feet away from the bathroom.

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Comments (5)

User
3 years ago
Worst idea ever. The humidity goes right back into the attic. The duct needs to go up and out the roof.
formulaross20
3 years ago
Ditto, if the breeze is coming from the wrong direction what you propose is the same as venting directly into the attic.
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Thanks PPF, I saw those. They say its is for 3" and 4" but it has a 4" hole and no sleeve mechanism. So my 3" duct penetrating through the roof will have to be enlarged above the roof cut and somehow joined to the receiver in the vent cap. There is <3/4" clearance between the base and the 4" receiver hole in the unit to accommodate a reducer without having to cut 4" into the roofing deck to make room. Reducers with clearance to join both ends would need 3-4". I can either fashion something and tape it all up and hope for the best or I can simply extend the 3" pipe into the 4" receiver as far as possible and hope that the general seal around 3/4 of the base of the unit is enough to allow the venting air to activate the baffle and exit without too much bleed. The unit also seems to have a really small base which does not provide much flashing surface to mount under the shingles. May not be a concern but it does seem to be narrower than other models. Thanks for the suggestion. I will have to think on it some more.
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PRO
Mint tile Minneapolis
3 years ago
We usually convert bath fans to ridgid pvc glue up runs and Pitch properly for moisture to run out not back into the fan assembly vertically thru a roof, rim joists are usuallly the ticket upper levels are challenging.
jmc_inwpg
Original Author
3 years ago
ok, thank you for that input. I will leave that vent alone, other than replacing the ugly bent looking grille. I thought it would have been an option rather than cutting a new hole. The other bathroom on the main floor vents out a side wall (northside of house) And i have never had any problems with it. The fan is installed on the ceiling about 4-5 feet away from the wall. Not sure what kind of treatment they did with that as it is original to the house. lol - that upper area on my side of house looks like a good spot. how about if i run pipe (not a flexible one) and insulate the pipe to a different spot and do same? (still kinda stuck there)

what if i did solid pipe to the vent and insulated it? and far enough away from attic vent so nothing flows back in that way? I've also seen vents that go on outside wall, and also ductless vents (did not look like a good choice).
cat_ky
3 years ago
The vent you are planning on using is a vent for your attic, it is not a good idea to use it for a vent, or to seal that vent up. Run your fan vent, through the roof where it is supposed to go, for best efficiency.

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