Hello,

Here is my stinky house problem. I live in a 2 story modular townhome. 3 bedrooms upstairs. The heater located downstairs. Whenever the air conditioner or heater is turned on the whole house smells like sewer. I had a plumber/hvac guy inspect my furnace and AC. Luckily, there was nothing wrong with the unit. However, he ended up spending 6 hours trying to figure out why it caused the house to stink. Well, he and I narrowed it down to the cold air return was pulling in the smell from somewhere to the return air vents to the blower unit. He had a camera that he used to snake into the vents and noticed some plumbing vent pipes but couldn't tell if there was a leak in them. His camera could only go so far and thus was unable to see all of the pipes. He discovered that some of the plumbing vent pipes in the attic were never connected or cemented to the vent pipes on the roof. He fixed those. But it still smells. It seems that the cold air returns in the different rooms are not a direct route to the blower. The air is pulled from the 3 bedrooms upstairs through the return air ducts that are just holes through the walls to the blower downstairs. So, the smell could be coming from anywhere inside the walls. Sure enough, if I put my nose to the return air vents I notice the smell now without running the blower. I am not sure what to do? How is something like this fixed? What kind of expense am I looking at? Please help! Ugghh!
-smellyhome

Smells and noises are the hardest for us to answer without being on site to check for ourselves. Have you considered running a smoke test on your vents?
He(the plumber) discovered that some of the plumbing vent pipes in the attic were never connected or cemented to the vent pipes on the roof. He fixed those. But it still smells. How many more vents, inside the walls, were never connected properly? A smoke test would tell you if you have unconnected vent pipes that are hidden inside walls. Couldn't hurt and might help. Also Ron came up with something I should have snapped to.
there could be stupid things like the AC condensate drain connected to the sewer line.
Good luck, Tom

Take some of the general smells: sewage, mold and mildew and dead animals in the walls.

For the latter two, something got wet inside the walls or Mold and mildew growing on the AC coils. Could be caused by a roof leak which was fixed long ago.

For the sewage smells, there could be stupid things like the AC condensate drain connected to the sewer line. Unused fixtures where the traps have dried out. Somebody may have accidentally drilled a hole in a PVC vent pipe. Venting issues.



Just suggestions.

Its quite common to use wall cavities are part of the return air duct, same for floor joist chases. It is also common that the plumber used the same chase or cavity for his venting pipe. If he failed to glue one jointhe may have failed to do more things so your job is a big one. Are you 100% positive this is sewer gas and not mold or mildew. Since you don't appear to do all of your own repair work its time to call a plumber rather than a HVAC outfit. Do you have any possible toilet wax ring leaks where one bathroom really smells 24/7 ?

Thanks for the responses. I am 99% sure its sewage gas. The bathrooms never smell. So I doubt it's a wax ring leak. I have had the problem for as long as I have lived here (5years). I live in a dry climate and really only use the ac for a couple of months in the summer. The rest of the time I always have a window open. So, once I finally turn on the blower I'm reminded I need to get that fixed. Again, thanks for the advice. I guess I will contact a new plumber.

-smellyhome