I would by lying if i told you that it will cause problems it may be totally fine.
Vent shower into attic.
First you ll partially block your roof vent with the piping reducing the flow of cooling air through your attic.
If you re tempted to vent your exhaust fan through an existing roof vent or even vent it into the attic don t do it.
Bathroom ventilation codes require a bathroom exhaust fan to vent to the exterior not the attic for health and structural reasons.
Because what happens is when the insulation gets moist from all that moisture that s being dumped into the attic it completely cuts down on the r value of the insulation.
The lowdown on venting your bath fan into an attic is that it can be done but it should terminate on the outside.
It cannot move air to a crawlspace or attic.
While this may seem obvious homeowners may out of convenience direct the vent into either of these locations.
Bathroom fan vent code requirements include no venting to attic areas to help reduce mold or structural problems.
Climb into the attic and clear away any insulation from around the hole.
Depending on the location of the bathroom it may be easy to vent the exhaust fan through the roof.
It eliminates the need for routing ductwork through the house and these fans usually dry the bathroom more quickly.
For optimum performance locate it between the shower and the toilet.
This section notes that air exhausted from the bathroom must be sent outdoors not indoors to the same residence or indoors to any other dwelling unit.
So you do need to get that vented outside whether it s through the siding with one of those trap doors that sort of opens out every time you ve got it on or through the soffit.
Bathroom exhaust fans perform an important function by removing excess moisture from your home.
The question about moist air reentering an attic through soffit vents after it has been blown out of an exhaust vent opening is a fair one but i don t think that s likely to be a significant building moisture source.
Second during cold winters you ll be blowing warm moist air onto a cold surface the roof vent and roof plywood.
If you vent the bathroom exhaust fan to close to the soffit vents which are vented plates under your homes outer edge and roof your home the air can be sucked right back into the attic from the soffit.
When venting a bathroom exhaust fan make sure to vent the air to the outside rather than into your attic where it can cause mold and mildew to form.
This involves running ductwork from the fan usually though an attic and out through the roof.
The truth about attic bathroom venting.
Draw a mark on the bathroom ceiling where you d like to install the vent fan.
Our article bathroom ventilation codes specs cites the importance of venting bath vent fans to the outdoors not into an attic or crawl space.
No you cannot vent the bathroom exhaust fan into the soffit vents.
