# Sewer gas smell in Master Bath - vent / trap problem - but what/where???



## Panzer5 (Oct 21, 2008)

After running a vac in the master bath, the smell of sewer gasses choked me out - seriously had to dash out. I mentioned it to the HO & she says they sometimes smell it after running the shower, but it always goes away...

Anyway, I checked the area below the joists & it looks like there are appropriate P traps on the relevant fixtures & it looks like theres a vent in the roof above the bathroom - so I'm stumped.

I talked to a plumber friend of mine - and he says 'smells can be notoriously hard to trace'. He's busy and can't come out till Friday.

Anything we can do to keep them from sucking sewer gasses into the house in the meantime? Any suggestions on how to isolate where the bad air is coming in? Theres a toilet, shower & double sink & no floor drain.


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## Inner10 (Mar 12, 2009)

Bad toilet gasket?


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## cleveman (Dec 28, 2007)

Yeah, check the toilet gasket. Extend the vent pipe on the roof also. This will make it suck harder. We'll see if any plumbers care to comment on that one.


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## griz (Nov 26, 2009)

Another possibility...the double sink.

1) Check for a clean out with the plug missing. 

2) Perhaps the sink was plumbed for two drain hook ups & only one was used. 

I have come across both these scenarios more than once...


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## go dart (Dec 6, 2005)

I think Cleveman is on to something. I've had this come up on a couple 2nd floor master baths we've remodeled way after we finished the remodel. What had happened is they had new roofs put on and during the reroof sometime the vent stack venting that bath either slipped or was accidently pushed down trapping water and now not venting. Check the attic you'll be able to tell. Good luck.


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## Oconomowoc (Oct 13, 2011)

Start by isolating the fixtures. It's easy to see if water is in the trap. That's a no brainer. 

Start by checking the sinks. Then check the shower. Shine a flashlight into the drain and see if the shower has water in the trap. 

Once you do that, have a person flush the toilet while you are looking at the shower drain with the flashlight. If you flush the toilet and you see the water in the shower trap drop or even move just a little you either have a blockage in the drain or in the vent.

If the vent is the problem odds are the blockage will be located at the juncture of where the horizontal drain for the lavatory connects to the vertical portion of the drain (wet vent).

Do this first before removing a toilet to check for a wax ring. This eliminates the other fixtures and isolates the problem to the toilet.

Pulling a toilet based on a guess doesn't make a whole lot of sense.

Mike


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## Oconomowoc (Oct 13, 2011)

cleveman said:


> Yeah, check the toilet gasket. Extend the vent pipe on the roof also. This will make it suck harder. We'll see if any plumbers care to comment on that one.


That doesn't make sense. Sucking harder?

Vents work better the shorter they are.

A vent is sized according to total load. The length (total developed length) in most residential applications falls WAY under the maximum limit. 

Now consider that, in Wisconsin at least, the vents are sized based on multiple fixtures being used at once. Even with every fixture running the vents are oversized according to our code book.

Also consider how much you would really add. If you put a couple feet on the termination it wouldn't even register as far as CFM is concerned. But like I say, making a vent longer makes the problem worse. An example would be snorkeling, try breathing through a 20 piece of 1" pipe vs 16". Shorter is easier.

Water in a horizontal run up in the attic? Yes, that can be a problem.

Mike


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## cleveman (Dec 28, 2007)

He's not having trouble getting the drains to drain. He's having trouble with gas coming out. I was having trouble smelling sewer gas and a more experienced plumber than I said to extend the vent on up. So I tacked on 2 feet or so and solved the problem.

It really sucks.


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## Oconomowoc (Oct 13, 2011)

A trap protects against sewer gas. That's plumbing in a nutshell.

2' on a stack mathematically makes no difference. I don't know what happened in your case but 2' on a vent stack that's usually pretty long doesn't change physics much.

Mike


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## kcremodeling (Nov 8, 2009)

Extending the pipe doesn't make any sense to me.:blink: If you are smelling gas their is an opening in the line. A plumbing system should be airtight, therefore there is now way gas can get into the living space.


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## bconley (Mar 8, 2009)

You've got a siphoning problem, make sure that they are actually P traps not S traps, S traps siphon more easily and could be why cleavmans stopped when extending the vent (less venting)


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## Inner10 (Mar 12, 2009)

Here I filled in the blanks for you guys:



> He's not having trouble getting the drains to drain. He's having trouble with gas coming out. I was having trouble smelling sewer gas _while I was working on my roof_ and a more experienced plumber than I said to extend the vent on up. So I tacked on 2 feet or so and solved the problem.


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## Tinstaafl (Jan 6, 2008)

I was actually thinking along those lines. If the vent stack isn't very high, and/or there's a downdraft, the smell could be coming from outside and extending the stack could raise the "plume of effluence" away from where it was getting in.


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## cleveman (Dec 28, 2007)

There is some truth to that. We were smelling it in the bottom of a basement being dug next door.


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