Septic odor when running bathroom fan

Lightwave · Dec 24, 2009

Whenever we run the main bathroom fan for more than a few minutes, one end of the house--the end with the main drain stack--smells of sewer/septic gas. The smell seems to originate in the first floor hallway outside a half bathroom. There is no plumbing in the hallway. There's no smell in the half bathroom. There is no plumbing in the shared wall between the hall and bathroom. The drain stack is in the bathroom's outside wall.

I suspect sewer gases are escaping through a leak in the drain stack, traveling through the first floor ceiling space, then entering the house through the hall ceiling.

What is the best approach to this problem? Call a plumber, call a leak detection outfit, open up the ceiling to visually inspect the stack?

Doherty Plumbing · Dec 25, 2009

Lightwave said:
Whenever we run the main bathroom fan for more than a few minutes, one end of the house--the end with the main drain stack--smells of sewer/septic gas. The smell seems to originate in the first floor hallway outside a half bathroom. There is no plumbing in the hallway. There's no smell in the half bathroom. There is no plumbing in the shared wall between the hall and bathroom. The drain stack is in the bathroom's outside wall.

I suspect sewer gases are escaping through a leak in the drain stack, traveling through the first floor ceiling space, then entering the house through the hall ceiling.

What is the best approach to this problem? Call a plumber, call a leak detection outfit, open up the ceiling to visually inspect the stack?

If you're sure that this is what's happening I'd open the wall up myself and have a look.....

Sponsor · 2022-01-29T12:20:58-0800

Krow · Dec 25, 2009

I'm thinking , it may not be a septic/sewer gas smell. Have you checked the fan ? Sometimes an overheated wire in an electrical fixture may cause a plasticky smell. Its possible the fan motor is starting to cease up. That would cause a funny odour as well.

Lightwave · Dec 29, 2009

The fan motor can be ruled out; anything that depressurizes the house causes the same effect.

We opened up the wall around the suspect pipe and found no signs of damage nor was the smell stronger near the pipe.

A cursory test using pine sol as a scent bomb didn't turn up any leads.

Next step will probably be to call a plumber to have a smoke test done.

Spaceman Spiff · Dec 30, 2009

Do you have a dry trap on a drain or a dry floor drain somewhere? Maybe a wax toilet ring that isn't sealing?

Omo1 · Oct 11, 2020

Lightwave said:
Whenever we run the main bathroom fan for more than a few minutes, one end of the house--the end with the main drain stack--smells of sewer/septic gas. The smell seems to originate in the first floor hallway outside a half bathroom. There is no plumbing in the hallway. There's no smell in the half bathroom. There is no plumbing in the shared wall between the hall and bathroom. The drain stack is in the bathroom's outside wall.

I suspect sewer gases are escaping through a leak in the drain stack, traveling through the first floor ceiling space, then entering the house through the hall ceiling.

What is the best approach to this problem? Call a plumber, call a leak detection outfit, open up the ceiling to visually inspect the stack?

Hello, I was wondering if you found out what was wrong and where the smell was coming from. I’m having the same problem now and I came across your post while trying to search about it. I hope to hear from you, thanks

Septic odor when running bathroom fan

Lightwave

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Doherty Plumbing

Journeyman & Gas Fitter

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Krow

Plumber

Lightwave

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Spaceman Spiff

Architect

Omo1

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