Sewer smell intermittently in house and ducts

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Drdadr

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Hello,
I have been trying to figure out the source of a sewer smell in our house. We bought the house and extensively remodeled and added on, with mostly all new plumbing. The house is a 2 story with basement (unfinished) and has well and septic. There is a sump pit and a secondary pit (I think for the basement drains which are kept “flushed” by an RO and softener waste lines) which has its own pump which lifts to the main sewer line. The main line goes to the septic tanks which also have a lift pump that goes into a berm system. Finally there is one vent stack on the roof, which I think was the existing stack before remodeling.

We get sewer gas-like smells intermittently but they are not primarily in the bathrooms, interestingly. They occur throughout the house.

One interesting pattern is that they seem to be much stronger when I am running a whole house attic fan, OR when I am running the ERV constantly (I don’t obviously do both at the same time). Finally, I do smell the odor coming out of the vents when the heat is on sometimes.

Builder and the plumbing subcontractor do not have an answer as yet for where this could be coming from. We hadn’t lived in the house before remodeling it but didn’t think the previous owner had these issues.

Any thoughts/theories appreciated. Thanks!
 

WorthFlorida

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Obviously, running the attic whole house fan you're creating a slight vacuum (low pressure) in the home sucking in gas. Either there is a dry trap somewhere or a vent pipe is open inside a wall. Is the vent piping cast iron, PVC or copper? If the furnace (forced air) is in the basement, start there. Is there a condensation drain for an air conditioner mounted on the furnace?

A smoke test can find leaks.
 

Drdadr

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The vent piping is all PVC. No obvious leaks. There is a condensate line on the furnace that goes down into a very small floor drain, but it has water in it (it’s not dry) and it doesn’t seem to smell when I put my nose right up to the floor drain.
 

WorthFlorida

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Find the source is always difficult with out a smoke test. My take is there is an open vent pipe or a fitting was never glued and it has come apart inside a wall. Since you can smell the odor with the attic fan running it eliminates the vent pipe running through the attic space to the roof. You sometime smell it when the heat is on! Most homes with forced air heating, (I had three of them) floor joist and wall studs are used for the return air. If there are wall vents for the return air, at the bottom sill plates are cut out. Floor joist used as returns, usually in the basement to provide the return from the wall studs are capped off with sheet metal.

I'm suspecting a vent pipe open somewhere is in a return wall stud cavity. To try to find it remove the grill and with a mirror check the wall cavities. Under normal circumstances there should not be anything other than perhaps electrical wire. Why you may ask? I had a new home built in Cicero, NY two story home with a basement. During construction and up to the final walk through for closing, the 3" stack from the 2nd floor bathrooms was never connected, just an open pipe. How it passed county inspection is a question. There was no water anywhere so the plumbing contractor never leaked tested or ran any water. Maybe there was no water when the appliances were installed.

The home inspector for your closing may have wiggle some pipes and something broke loose.
 

Drdadr

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Find the source is always difficult with out a smoke test. My take is there is an open vent pipe or a fitting was never glued and it has come apart inside a wall. Since you can smell the odor with the attic fan running it eliminates the vent pipe running through the attic space to the roof. You sometime smell it when the heat is on! Most homes with forced air heating, (I had three of them) floor joist and wall studs are used for the return air. If there are wall vents for the return air, at the bottom sill plates are cut out. Floor joist used as returns, usually in the basement to provide the return from the wall studs are capped off with sheet metal.

I'm suspecting a vent pipe open somewhere is in a return wall stud cavity. To try to find it remove the grill and with a mirror check the wall cavities. Under normal circumstances there should not be anything other than perhaps electrical wire. Why you may ask? I had a new home built in Cicero, NY two story home with a basement. During construction and up to the final walk through for closing, the 3" stack from the 2nd floor bathrooms was never connected, just an open pipe. How it passed county inspection is a question. There was no water anywhere so the plumbing contractor never leaked tested or ran any water. Maybe there was no water when the appliances were installed.

The home inspector for your closing may have wiggle some pipes and something broke loose.
Great advice, thanks!
 
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