View Full Version : Bathroom Exhaust Fan Venting

02-04-2006, 11:44 AM
Checking into my attic I noticed the bathroom exhaust fan vents directly into the attic , not outside.

The plumbing vent stacks are close to the fan vents.

Is there any reason why these could not be venteed to the outside using the plumbing vent stacks?

02-04-2006, 12:08 PM
You cannot vent the bathroom out the drain vent stack. It is also a good idea to get this outside, either through the roof, gable, or sidewall. Adding moisture to the attic is not a great idea.

02-04-2006, 12:29 PM
Why can't you use the vent stack?

02-04-2006, 12:52 PM
A couple of reasons I can think of (as noted I'm not a pro), first, you'd have an opening into your bathroom when the fan wasn't running for all of the sewer gasses coming up from the sewer - not healthy or pleasant, and two, you'd be partially presurizing the drain system, possibly compromising draining of the waste everywhere else in the house. It would never pass a house inspection, either, so you'd have to change it before you could sell the house.

02-04-2006, 12:53 PM
Mixing plumbing vents with your bath fan is not good.

You really don't want sewer gas in your home do you?

They do make roof jacks for fans that have 4" openings for the ducting.
They take little time to install.

In addition, rain water goes down plumbing vents. Do you want water dripping into your bathroom ceiling?

02-06-2006, 04:50 AM
Thanks ,

Now I understand!

02-10-2006, 07:58 PM

When we use our bathroom to shower in the morning and turn the exhaust fan on when we start, after showering the ceiling fan grate drips water to the floor. This happens only in winter. The fan exhausts into the attic through a 3-inch pipe to the inside top of the roof at a roof vent. What can I do to prevent the water drips?

Paul R.

02-10-2006, 08:09 PM
Insulate the exhaust vent will help at least a little bit. The moisture condenses on the cold vent in the attic. If you can keep it warm enough until it exhausts, you'll limit the condensation.