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Question DetailsAsked on 7/10/2017

130 yr old farmhouse has a sewer gas smell that comes and goes.

130 yr old foursquare farmhouse. The smell comes and goes but is centralized to the center of the house first and second floor. It seems to be coming up a vent running along side a cinder block chimney that was added sometime after the house was built. This is the only vent to the second floor and the duct is caped off in the basement with an old coffee can so the duct is not connected t anything at this time. There is a basement under this part of the house. It does not seem to be coming from the gas vent pipe as that is about 6' away from the vent and the odor does not hover there. There is a bathroom on the main floor in the area in which the smell hovers on the first floor. The basement seems to have less of an odor but it can be smelled down there. There is only one bathroom in the house so there are no standing pipes. We've used an organic drain cleaner to try to clean out any residual bacteria in the pipes. Don't seem to notice any pattern to when the smell comes or goes

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1 Answer


If truly a sewer gas smell (as opposed to a sooty damp abandoned flue smell), then I would be looking at the drain lines, maybe if there is a stuck Studor vent (air admittance valve) under the basin in lieu of a proper sewer vent line through the roof.

Certainly if the duct from the basement is tin-canned off, try duct taping that - or pull the can off and smell right at the duct to see if that is the source - could be old creosote or coal dust or such buildup, which can smell pretty rank when it gets damp. (And of course, that vent, if a flue through the roof, should be capped at the top too to outside moisture can't get in). Or if this is the sewer vent pipe which someone for some reason cut, then you could be getting raw sewage gas from it - though if you stick your nose to it should smell sewer smell pretty much any time. Would at least airtight cap that even if not needed.

Could be (I have seen this) someone cut the sewer vent line to use it as a sewer line routing access point and never pult it back together, just putting the tin can over it temporarily and never came back to it. (Commonly 1-1/2 or 2" pipe versus the normal #" or 4" drain/sewer line).

The "gas vent pipe" 6' away - unless this goes continuous to the roof (the sewer vent pipe), I would look into what it is - should not open into the basement - could be an old oill tank vent pipe, sewer vent that was not take to the roof, a sewer cleanout without a cap on it, etc - any of which might stink.

The no pattern to when it occurs is probably related to differences in natural household venting - as indoor and outdoor tempearatures change seaswonally or through the day causing changes in airflow in the house (or possibly "stack effect" partial vacuum in the basement during parts of the day allowing subsoil leakage odors to get into the house). Can also be related to wind direction or strength as changes cause different venting direction and airflow in the house. And of course HVAC system operation and/or opening windows can also affect this airflow.

I would also look for a floor drain or basement wash tub drain which might have gone dry - you have to flush out with fresh water (about a gallon or more) every year (more often in dry areas) - a bit of lemon-scented dish soap added to it can help sweeten it up. if a drain goes dry, then sewer gases will leak out - and if the water level is low but not quite dry yet, when you flush or run large amounts of water (like when washer or tub empties) it can force sewer gas past the water in the trap, but only then. Flush any such drain out and leave topped off with water and see if it makes a difference.

Answered 3 years ago by LCD

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