I'm at a loss for the source of the sewer smell that permeates my house when my A/C is on. I've looked at a few things, but none have fixed the problem. First some info on the house and equipment:

3-floor house (including full basement).
HVAC system in it's own utility room in the basement (smell NOT in that room)
Smell is most prominent on one side of the house (East side), the utility room is in the southeast corner. Smell does not come out of the vents on the opposite side of house.
Humidifier on A/C drains into sewer drain in the utility room (but no smell from there)
Had A/C cleaned

My next step was going to be having the vents cleaned, but not sure that is the right step.

Thanks in advance!

 

Where does the drain for the evaporator coil drain to?

 

It drains via pvc pipe into a drain in the floor (near the HVAC unit). It's like a show drain - just larger. It doesn't smell there.

 

If it was a smell introduced into the A/C system via the returns.... you'd smell it all registers.

Since you only smell it in certain places it's not likely caused by the A/C.
Are there bathrooms in the areas where the smells are ?
There may be a disconnected or broken vent line in that area.

 

Does the drain that you see run water when the system is cooling?
( Is it the primary or secondary drain that you describe?)

 

Yes, I do hear water dripping/flowing when the A/C is on.
This is the side of the unit pic

This is the back drain area (ignore the water, I knocked over my water while poking around)

This is the Humidifier which is the 2nd pvc you see on the back side


Today when I got home from work, the whole house smelled (except any room with a door closed, including the utility room).

Someone mentioned it could be a drain stack break- How do I determine that? I do have a bathroom in the basement. Someone I work with mentioned it could be backup of gas from there due to lack of use- I ran the shower, flushed a few times and ran the sink today, see if that's it.

thanks

 

As far as I can see.... your A/C condensate line is setup with no trap. That is one good way to extract odors from that floor drain.

What is that white PVC with the red arrow doing ??



If sinks, bathtubs, showers (anything with a trap)aren't used regularly then the water in the trap can evaporate and allow sewer gases in that way. Just refill them with water occasionally to stop the problem.

 

Have you considered the possibility of a dead animal, rotting fruit/vegetable, or evil roommate putting cheese somewhere? I think it is more likely that the AC unit is just moving the smell around your house through normal air circulation.