View Full Version : bathroom fan exhaust

03-15-2007, 12:39 PM
I have read several threads that reference "soffit vents" for bathroom exhaust fans. I am installing a new light/fan combination, and would like to do it right. The bathroom had been vented directly into the attic, above the insulation. I don't see any evidence of moisture condensation or damage to the structure or insulation.

I have a tile roof (still original from 1914) that I really don't want to try to penetrate.

The vent is 5.5' from the exterior wall, in the ceiling. I can run a 4" vent to the soffit without any problem. The vent line would not have any slope. I live in Central Illinois.

1.Does anyone see potential problems?
2.Does anyone have alternative suggestions to a soffit vent?
3.What does a soffit vent look like?
4.Does a soffit vent have a "flap" to prevent air flow when the fan isn't running?

Jim S.

03-15-2007, 01:15 PM
The sofit is the area under the eave of the roof. Often, there is a screen or grill there to allow airflow up to the peak to ventilate the attic. Installing a bathroom vent into this area is not ideal, since it blocks some of that area, and, while blowing the moist air out, everything next to it is being sucked into the attic by natural convection. If you can't go through the roof, the next best location is the end gable wall, then maybe through the joists to the outside wall, and third, the sofit area. You don't want to blow it into the attic, but if there is good ventilation in that attic, and you don't have a cold winter, you may not notice any condensation.

04-08-2007, 06:51 PM
Hi, I'm not an expert but I've been doing some research in this area as I'm remodeling both of my bathrooms and I want to make sure they pass code. I live a little further north than you so I'm sure our codes are a bit different as I know venting through the sofit would not pass code here. The way I would reccommend from what I've read, is to come straight up from the bathroom and then run your exhaust on a slight down grade to the gable end. You can then attach a flapper type cap on the outside end, much like a dryer vent. The reason for running the pipe on a slight down grade is, in case there is any condensation buildup due to cold temperatures, it will run out the pipe and not back into the fan. Up here, although the code does not require it, I'd consider adding an insulated sleve over the pipe just to reduce the chance of condenstation, but then again, we get 4 months of sub-zero weather.

Just trying to help :)

04-08-2007, 08:39 PM
... don't see any evidence of moisture condensation or damage to the structure or insulation.
.... The vent line would not have any slope. I live in Central Illinois. .... Whenever warm indoor air hits subzero outdoor air, mist results. This is what your dryer air might like look like on a winter day. This is condensation in mid air. Looks like steam, but it's cold mist.

In a vent conduit, there will be condensation. If you can slope your newly proprosed conduit by only one inch, you will enable the moisture to drip out. Otherwise it will sit on the bottom of the tube until it evaporates. Not optimal.


04-09-2007, 07:34 AM
I appreciate the wise input! I will put it to good use. :) Thanks!