Why does my bathroom stink?

April 26, 2015 11:47 AM

A few years ago, I had an attic fan installed to reduce heat build-up on the second floor of my home. Ever since, I have noticed foul sewage odors in my first-floor half bath. The odor is only present when the attic fan is running. What is causing the foul smell, and what can I do to solve this problem?

The attic fan seems powerful and does the job of regulating temperatures in my home very effectively. An HVAC contractor installed the fan. The smell always orginates in the bathroom, which contains a toilet, small sink, a bathroom fan and a heat/AC register. I cannot tell where the smell is coming from. When the attic fan has been running for a while, the smell tends to drift from the bathroom into the adjacent rooms.

posted by rdauphin to Home & Garden (9 answers total)

Totally working with knowledge gleaned from "Modern Jackass magazine" here, but in most municipalities you have to have a sort of relief vent for sewer gases in bathrooms. Generally it's a pipe that bleeds air out of the wastewater system as your sink and toilet drains. Sort of sounds to me like there could be a crack or a gap in the pipe somewhere as it moves through your attic and out the top of your house. The fan is moving the smell of the system around. I would assume a plumber could have a look at the system to make sure your toilet's wax seal is intact and the traps in your sink aren't dry—and there are no cracks in the vent pipe?
posted by littlerobothead at 12:00 PM on April 26, 2015

Assuming this is an attic fan (as in a fan that pulls air from the attic rather than a whole house fan that pulls air from the house itself), air is being pulled out of the house when the attic is being depressurized by the fan. Either you have insufficient ventilation in the attic (not enough space for air to come in to replace air going out via the fan) or the fan is just too powerful. When the house is depressurized, air is being pulled up from the waste plumbing. You likely have a small hole somewhere in the plumbing system or something installed wrong.

You don't want to be depressurizing your house as this can cause problem with any gas appliances, might be a radon risk, etc. So make sure you have sufficient free air space to vent the attic (soffit, gable and ridge vents) and make sure the fan is properly sized. You could also look at air sealing between the house and attic. You should also get a plumber to have a look to see where the leak might be.
posted by ssg at 12:04 PM on April 26, 2015

Response by poster: It is an attic fan which pulls heat from the attic, not a whole house fan (though I do have both, but rarely use the whole house fan). I have made sure the sink trap is not dry. But I have noticed the toilet rocks a bit. Is that a sign the wax seal is not seated properly?
posted by rdauphin at 12:35 PM on April 26, 2015

Well you just debunked my theory about a problem with the P-trap in your sink. But just for good measure, what if you tried sealing off the sink drain completely with duct tape? If the smell was gone (or much weaker) you could at least narrow the problem down to the sink drain.

To test your theory about the toilet wax seal, maybe you could do a similar sealing maneuver over the entire toilet. Maybe get a big contractor garbage bag, throw it over the toilet, and use duct tape to seal the entire perimeter to the wall/floor?

It sure seems like it's got to be one of those two fixtures.
posted by reeddavid at 3:51 PM on April 26, 2015

Do you have a floor drain in the bathroom?
posted by Zedcaster at 3:55 PM on April 26, 2015

But I have noticed the toilet rocks a bit. Is that a sign the wax seal is not seated properly?

Could be. Can you try tightening the bolts and checking if that helps?
posted by ssg at 4:22 PM on April 26, 2015

It could be you wax seal. Your toilet shouldn't move so you could have other issues like a rotted floor or bad pipe seal or the bolts could just be loose. Either way it could be causing your sewer gas smell.
posted by Mitheral at 4:23 PM on April 26, 2015

If the toilet is already rocking, don't come up with an elaborate testing process -- it's probably a good idea to replace the wax seal anyway, so just unbolt it, remove the wax ring, and check for any damage to the flange -- which hopefully is PVC but in older homes is possibly a lead pipe fitting. If the toilet can't fully bolt itself to the flange it will rock, and you'll need a new flange (which is probably a plumber job, though I've done it). Wax seals are very inexpensive and meant to be easily replaced, though, so just do it. While the toilet itself is up you should be able to get a VERY good idea if there's any leakage, rotted subfloor, and so on. I also assure you that this is a much less messy job than you expect going in, but it might help to have a spotter while moving the toilet base.
posted by dhartung at 5:40 PM on April 26, 2015

Response by poster: Many thanks to responders. I will give these ideas a try. Since I'm unable to handle the toilet issues myself, I will seek out a plumber. The toilet was a replacement installed about 3 years ago, so perhaps it was never properly sealed. The timeline fits.

About 6 years ago, the small bathroom was remodeled and I recall seeing the flange and the flooring underneath in very good shape. I'll check it out again.
posted by rdauphin at 4:08 AM on April 27, 2015