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Re: sewer gas in house

We also had sewer gas issues. Reason was, plumbing had been added during a remodel and the new waste plumbing was not attached to a pipe the vent stack is attached to. We ran a 1.5" pvc pipe as a vent pipe from the added plumbing out through the sill plate and the odor is gone. So, you might look to verify all waste pipes are connected to your vent stack.

Re: sewer gas in house
laguna1 wrote:

I'm having a problem with sewer gas venting into the house. We can't determine where the gas is originating except from the basement. It comes mostly from using alot of water at one time. Such as: 2 showers and 3 wash loads. The smell is at it's worst when the wind is from the South and West (vent is on the W slope of the roof). We have a septic system and the house is 30 yrs old. This has been an on going problem since we built. We recently had the basement permasealed with an enclosed sump pump. The smell was much better a year ago when the basement was sealed for leaks in the foundation but now the odor is back.

Sewer gas smells almost always come from a lost trap seal somewhere in the system. They hardly ever come from some kind of leak in the drain system, and if they do, you would see dripping water at that leak. This includes the wax seal on the base of the toilet.

Traps need to be protected from siphoning (negative pressure) or from burping (positive pressure) by properly placed vents.

In your case, the smell usually follows heavy use of the plumbing--the reason is probably because heavy use fills the drains more, thereby creating pressure fluctuations in the system, with the potential to siphon traps, or cause them to burp. (Siphoning is more likely the problem.) Wind direction can also affect whether or not a trap whose water seal has been lost gives off sewer gas, because wind can affect pressures within the system, but wind, by itself, would not siphon a trap.

You can isolate/identify which trap is causing the trouble:
On a day when you notice the smell, go to the lowest cleanout in the house and remove the plug; pour in a small bottle of peppermint oil and replace the plug; close all windows and doors; turn on all exhaust fans in the house, including the clothes dryer and range hood--you are aiming to de-pressurize the house as much as possible. Now, go around to each drain opening and sniff for peppermint.

The trap(s) that smell strong have lost their seal, and have a problem with a vent that should be protecting them from pressure fluctuations. How to fix the vent is another problem, but at least you will know the culprit. In some cases,the fix can be as easy as installing an Air Admittance Valve at the fixture that is causing the trouble.

Re: sewer gas in house

First post so I'm a bit shy about tagging onto this thread but hopefully that is ok.

What if the smell is only outside?

We just moved into a new house and are getting on and off smell of sewer gas outside the house. There is no smell inside and I think the gas is coming from the roof vents.

The septic is new in that it was build for this house but it was installed probably 5 years or more ago and so this is the first time it has really been used. Up until now it was essentially dry.

Half the sites I see on the web say a gas smell is normal, ignore it or if it bothers you put filters on the vents. The other half say thats a terrible idea because gas smell is an indication of a problem and you don't want to cover it up and ignore the warnings.

Any suggestions regarding who is correct I'd very much appreciate it.

Re: sewer gas in house

i have found that the quickest and most accurate way to find your problem is to do a smoke test!! if you have a sewer gas leak it is from a drain or vent pipe that is broken!! You will probably need to call you local plumber because in most cases the local fire department needs to be notified before the test is done but you should be able to identify where the gas is coming from


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