Sewer gas in bathroom when attic fan is on. Found a dead critter

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JeffeVerde

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I'm suddenly smelling sewer gas in a bathroom when the attic fan is on, and I can't figure out the source (and yes, I flushed :p ). We use the attic fan daily, and the smell just started today. Turn the attic fan on, and you get the sewer gas within a minute or two. Turn the fan off, and once the smell dissipates there's no more sewer gas smell. I have -
  • run water at all the fixtures to ensure the traps are full
  • filled the sinks and tub with water and blocked the overflows
  • cleaned the traps on both sinks
The really odd thing is that the smell is strongest at the bathroom entrance, and I don't detect the smell at either of the sinks - even when I had the traps off.

The attic fan blows into the attic and then passively vents through the gable and ridge vents. So the attic is pressurized when the fan is on. The house was built in 2014 and it has ABS waste piping.

What's the next step? I'm stumped.
 

wwhitney

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Does the bathroom have a window, and if you open it first does the attic fan still cause the smell?

Is there a smell in the attic before you turn the attic fan on?

Cheers, Wayne
 

WorthFlorida

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Something changed recently. May not have as many windows open as before and you're pulling air through a traps though it is filled with water. Possible a vent pipe fitting was not cemented and came apart in the wall or crawl space? It's all a wild ass guess.

A possibility is the roof vent is nearby the bathroom window. With the right wind direction the odor is coming out of the roof vent and getting pulled into the home through a window. It is what Wayne is suggesting.

Get some punks. They make smoke so you can see where the airflow (odor) might be coming from. Search on Amazon "Un-scented 100 pack stick incense". You might find them in stores selling halloween stuff this time of the year.
 

wwhitney

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you're pulling air through a traps though it is filled with water.
But the trap seal depth is supposed to be at least 2" deep, so that would require a fan that could depressurize the bathroom by more than 2" w.c. Are attic whole house fans that powerful, given that they are used with the windows open? The OP reports filling the sinks and tubs with water, effectively increasing their trap depths, so that rules out an air path through their traps.

There could still be a hole in a DWV pipe downstream of the trap. Or a loose slip joint fitting on the lav trap arms. My first thought was a failed wax seal at the toilet.

A possibility is the roof vent is nearby the bathroom window. With the right wind direction the odor is coming out of the roof vent and getting pulled into the home through a window. It is what Wayne is suggesting.
Not actually my intention, I was just trying to figure out if the bathroom is being depressurized much. With a window open, it shouldn't be depressurized much. Particularly with a window open and the bathroom door closed (assuming the whole house exhaust fan is outside the bathroom), any air sucked through the gaps around the door should be easily replaced through the window.

Cheers, Wayne
 

stardust

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When I installed a bathroom fan for my brother, suddenly there was sewer gas smell whenever it was turned on. Using just my nose, I located it to be at the rear of the toilet where there was no toilet-to-floor sealant. This was in Europe, so I didn't know if wax or rubber toilet seals were more common. There was no visible water escaping, and it's all concrete and tile anyway, so I caulked the back of the toilet to the floor, and it solved the smell problem.

If I had more time and tools, I would've pulled the toilet to inspect and replace the seal. Much more critical in a wood framed building.
 

Reach4

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The OP reports filling the sinks and tubs with water, effectively increasing their trap depths, so that rules out an air path through their traps.
I presume the stoppers are closed. The overflows provide a path not affected by what is in the tub or bowl.
 

JeffeVerde

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Thanks for the suggestions. I -
  • tested with the bathroom window closed
  • tested with the door to the tub and toilet room closed and sealed with a towel (no smell in the tub/toilet room)
  • removed the traps for both sinks and sealed the drain stub-out with a heavy plastic bag and rubberbands.
  • recent knee and shoulder surgery precludes getting in the attic, but I stuck my head in the hatch with the attic fan running. Plenty of hot air coming out, but no eau do sewer
Is it realistic that I could be smelling an open vent inside the walls, through the drywall? So next step is to smoke test around all the wall penetrations (medicine cabinet and 8 electrical boxes - including two light fixtures on the wall where the vent is probably located)
 

Reach4

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Another test is called the "peppermint test" where a peppermint oil + hot water mix is poured down a vent pipe by somebody who will not be sniffing around inside.

So if the smell is from a source outside of the plumbing, you should not smell the peppermint inside. If you do that, solicit some younger helpers with more-sensitive noses.
 

wwhitney

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So try testing with the bathroom window open, see if you still get the smell (and if you do, try again with the window open and the door closed). If not, then it's definitely from depressurizing the bathroom and pulling in an odor, probably from the DWV system. I assume you have a lot of other windows open when using the fan?

I think it's plausible that someone could have drilled a hole in a vent inadvertently, say, and when you depressurize the bathroom, it pulls in air from the DWV through that hole in the vent. Or an air leak at the toilet to closet flange seal, or on any of the other drains.

Cheers, Wayne
 

JeffeVerde

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The problem has gotten worse. Now, the smell is continuous, regardless of the attic fan. And it's definitely specific to the sink area. If I close the door to the (separate) toilet/tub area, and open the window and turn on the fan in that room, the tub/toilet room stays fresh, while the sink area continues to smell like a pit latrine.

I opened the other side of the plumbing wall and there are no leaks and no smell from that side. I even opened the vent stack to see if it's blocked. I can see daylight up the vent, and more notably, there's no sewer smell coming up from the wet stack below (this bathroom is on the second floor). I also tried pulling the traps on the sink drains and putting test plugs in the stubouts, with no change in the smell. So the smell is definitely not coming in from the sink drains.

The 1st floor wall that caries the problem bathroom's drain down to the slab, is offset about 18" into the problem bathroom (roughly at the front of the bathroom cabinet), and I think the tub and toilet drains also tie into that riser. I'm wondering if that's where the problem is, and the gas is coming up through the unfinished floor under the cabinet. Next step is to open the ceiling below to get eyes (and nose) on that section of the drain.
 

JeffeVerde

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After opening the wall and downstairs ceiling in six places trying to identify where the smell was coming from, I finally tracked it down. A dead critter in the toe kick base of the bathroom cabinet. I *think* it was a gopher, but hard to tell - it was kind of bloated after a week. There's no plumbing or electrical in the toe kick, so no clue how it got in there . . . 15' from the nearest exterior wall . . . on the second floor.
 

Terry

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The home I grew up in had a bad smell in the hall bathroom. When I became a plumber, I wound up removing the drywall, replaced the bathtub, vanity and did new flooring. I found a small nest of dead mice, and also where rats had been peeing inside the other wall. There was a wall hung toilet on that side, so the wall had been spaced out, leaving lot's of running room for rats back and forth. The ceiling had been dropped for a light fixture, and there was running room there too.
I wound up blocking everything up, and painting over the urine with ZeroLac. They use that after fires in homes too. All those years my mother thought it was the boys in the family, but nope, those dirty rats were giving us a bad name.
 
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