Smell when furnace is running/heater /air conditioner running

[Kos2kos]

when the furnaces running either on heat or AC it's pulling air out of the drain in the washer room, which is bringing in smells from that drainpipe, as far as we could tell there's a trap on that pipe, drain. but this happens on both units/slab construction, when the furnace is not running there's no smell,. The plumbing's approximate 25 years old PVC.. Any thoughts?

 

[Breplum]

Modern efficiency standards for HVAC equipment makes clear that there should be no leaks, so look to seal all leaky equipment regardless of the plumbing.
I'll guess that you do have HVAC airflow leaks. Return air side is a first place to check.
If there is water in the 'drain' there should not be smell unless fouled with detritus.
Beyond that, the nose is your best bet, sniffing close to any possible source.

 

[Sponsor]

 

[L squad]

I had a friend who had a smelly furnace. Turns out the condensate line was clogged. all the water created by the A/C was about 2 inches deep in the drain pan just sitting there stale. it just blew the stink around every time it was turned on.. After the water was drained the smell went away. Otherwise I agree, the return should be totally sealed and not pulling ambient air. get a smoke pen and some mastic or foil tape and lock those holes down.

 

[Kos2kos]

I had a friend who had a smelly furnace. Turns out the condensate line was clogged. all the water created by the A/C was about 2 inches deep in the drain pan just sitting there stale. it just blew the stink around every time it was turned on.. After the water was drained the smell went away. Otherwise I agree, the return should be totally sealed and not pulling ambient air. get a smoke pen and some mastic or foil tape and lock those holes down.

appreciate the feedback guys.. We smoked pen it. The building so tight that it's sucking the door shut in the buildings and when the furnace is on heat or AC it's pulling the stank out of the washer drain system somehow,. were going to cut into the wall and look at the trap /drained system next ..this is happening on both units. It's a two family the one side doesn't even have air /ductwork installed , it happens when the exhaust fan is on in the bathroom.. on the second unit.. thanks for your input..

 

[John Gayewski]

Yeah check the coil, but when in heating mode there will be no condensation on the coil and it would dry any "stale" water.

Are you sure extended heating stints cause a smell?

 

[L squad]

Building may be tight. But if the door to the furnace room is being pulled closed, then the system seems to have a massive hole in it. From my understanding. All the air entering the system should come from the returns. Not the room the furnace is in.

 

[LLigetfa]

But if the door to the furnace room is being pulled closed, then the system seems to have a massive hole in it.

OP did not say which door is being pulled shut. If it is the door to the room that the washer drain is in, then the air registers are not properly balanced. If you prop the door open and the stink subsides, it is likely a HVAC problem, not a plumbing issue.