One of the plumbing traps may be dry and need water put in them.

Or there may be a bad connection to the vent stack somewhere.

Do you periodically run water through basement floor drains? It the traps dry out the smell comes in.

Thanks. The basement drains get flushed because the refrigerator RO filter and the softener waste go into them. There are no dry traps that I can see in the basement.

We had that smell in our old house and it was coming from the HVAC drain.

When we bought our previous house we also had a sewer smell in the master bath. It was a bad/old wax ring on the toilet letting the gases seep into the room.

In the interest of covering all the bases, have you analyzed your families diet over the past month or so?

We have the same problem and I hate not knowing why. A plumber suggested they do a 'smoke test'... same as yours, at times the smell arises during duct blowing. More at nighttime.

Check the plumbing vent stacks for obstructions such as animal nests and fallen debris. I called plumbing drain specialists and they all refused to go on the roof and check them. Had to do it myself. Even though vertigo and ladders don't mix well.

Checking, worthy if you'd tell why they'd refuse? it's not a "plumber's job"?

"We don't go on roofs. We only do drains."

Just running a garden hose into it can clear the obstruction.

We're building new and before drywall noticed a sewer vent pipe had been disconnected to do a pressure check, and they never got around to reconnecting. Could be that simple.

"Just running a garden hose into it can clear the obstruction."

Running a garden hose in it will make it a drain, then the plumber can clean the drain.

Plumbers around here don't mind checking out the vent stacks on the roof. I guess that's another point for low-pitched ranch houses? :)

I had a stinky old sink from a clogged overflow. It wasn't hard to locate though...

Chimney, roof and plumbing vent covers to protect against animal intrusion are a must here in Raccoon City. Sooner better than later... :-((

Check cheater vents, if any. They are notoriously unreliable.

In my experience, sewer gas odor is usually the result of dry traps or bad seals on toilets.

In your case, it's likely that existing vent and/or drain lines were cut during remodeling so they could be tied into. It may be that a rag or something similar was stuffed up one of them to prevent odors pending connection of new piping, but didn't get removed. I suggest you focus on those areas where old meets new.

At a house we had built some years ago, the regular electrician wasn't available when the builder was ready to have bathroom lights installed. The new guy managed to puncture a vent stack behind my vanity. We had several short trips scheduled shortly after completion and each time we returned to no odors, but the smell was awful the next day. After exploring other possibilities, the builder was ready to tear up the shower floor when I asked about the odds of a nail or screw hitting a pipe, since we'd had something similar happen in another new house. He was relieved that the solution was much easier (and cheaper) than he'd feared.

Good luck on finding a solution soon!

JP, please tell how small hole was found..?

That was my question, how would they find the small hole?

Have someone make sure your whole house fan, ERV and myriad bath/ kitchen fans are balanced. Sounds like perhaps your WHF and ERV may be drawing negative pressure. You can address the sewer gas but it won’t stay away if there’s sucking pressure drawing it into the building envelope.

Know where you

Know where each vent stack is and note nails or screws in the wall. You can’t always feel the passage through pvc with a powered screwdriver

Everdebz and David F, my husband checked the attic to see the location of the vent stack before the builder returned and he made a (good) guess. Years before, we had a shower leak due to someone nailing into a supply pipe. That builder removed a section of drywall between the water closet and the shower and located the nail. I suggested to the builder that he remove the light fixture above my vanity and cut out some drywall to investigate. I figured that repair was minor compared to what the builder had proposed trying next. His regular electrician wouldn't have made that mistake, but the new guy did. We got lucky it was a relatively easy fix.

Before that day, the builder had already had the drains scoped and the vent stack visually checked from the roof, and had tried a few other things that I wasn't on hand to observe. He became convinced the problem was a poorly built shower pan and intended to tear it up. It would have taken weeks, if not months, to complete since the tile used was not available locally.

I’ll ask this just in case, since the smell gets stirred up when you run the attic fan could there be a dead animal somewhere. My parents had a vole that got hung in yarn in a basket and died in their basement and that thing stunk for a long time. They weren’t sure if it was sewer or dead animal until they discovered the little creature.

Our ongoing sewer smell turned out to be a drain line stub that was left open, way up near the ceiling in an unfinished basement. Took a lot longer than it should have to find it.

Glad they found the problem!

Yes. Besides the odor, we don't swallow the water out of bathroom sink. Have to call plumber. Sometimes odor seems to worsen when using faucet water.