AC drain pipe vent trap going dry - sewage smell

9031 Views 6 Replies 4 Participants Last post by Wildie, Apr 26, 2011

denemante

Discussion Starter · Apr 26, 2011

Hey all,

I'm nearly done my basement remodel. Original construction had the HWH near the big main house drain pipe. Tapped into that was a set of smaller pipes. They make a single exit from the main drain. Then it sprouts upward 3 feet to a Studor vent. Off the bottom of that is a trap, which leads to an open top pipe also 3 feet tall standing next to the Studor vent pipe. The only apparent purpose to this open pipe was that the HWH had a copper pipe running out of it and into this pipe - presumably emergency HWH overflow.

In the past, on rare occasions, I'd notice the faintest sewer smell. We also once had a fly bloom down there - not the little triangle dumb/slow looking fruit fly types - but your classic "fly". Never happened again. Could have been unrelated.

We had some HVAC work done and the HWH moved. Now, the HVAC guy has run a PVC drain for AC overflow to this existing same open-top pipe that leads to the main drain. The HWH continues to have its overflow running there too.

I realzed that previously, the HWH probably never overflowed - so the trap in that drain was likely bone dry - probably where the smell came from as this is on the main house drain.

Now with HVAC AC drain running into it - that will keep the trap wet in summer months when AC is running.

But not in the winter. I pointed this out to the plumber. He showed me this little flip-valve on the HWH overflow. Open it briefly, and it drains hot water into that drain - to wet the trap. He just said to do it on occasion.

This just simply doesn't seem right. So I'm trying to think premptively - could I simply tightly enclose the open top of this HVAC/HWH drain in question with spray foam or even plumbers tape or silicone? Then - who care is the trap goes try in the winter. Maybe sealing it would keep it more moist in there anyway.

My main concern is that before, this was all out in a big open room. But now, it's in a one-foot wide space behind a wall that's open to my new HVAC/HWH area. I don't want those units sucking sewer gas out of this drain and spreading it through my house...

Thoughts?

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AllanJ

· #2 · Apr 26, 2011 (Edited)

Don't trip the water heater overflow (pressure & temperature relief valve) too often, twice a year is enough. If you need water to fill the trap, bring it downstairs in a pitcher or watering can.

Heating and air conditioning units should suck air for climate control via a return air vent coming down from the house, not relying on basement air unless there are heat or cool air registers with more square inches in the basement. HVAC equipment partitioned off and needing intake air must have louvers to the outside or louvers to the rest of the basement. Combustion air should come from a louver or intake pipe to the outside.

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Wildie

· #3 · Apr 26, 2011

I have a/c and a forced air furnace. There is small pump beside the furnace that pumps the a/c condensate through a 3/8" plastic tube to a drain in the same manner as yours.
The furnace has a humidifier attached and it also has an over-flow connected to the condensate pump.
In the winter the humidifier over-flow maintains the drain trap and the a/c does the job in the summer.

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denemante

Discussion Starter · #4 · Apr 26, 2011

Once drywall is up - I'll have no way to reach this pipe to manually pour water into it. The only source would be AC overflow and the HWH. The plumber didn't say I should only use that release valve only about twice per year - he said I should do it anytime I think the trap is dry. Is that ill-advised?

My only other choice is to run my own PVC to that drain pipe in question so I can access it from a few feet away.

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denemante

Discussion Starter · #5 · Apr 26, 2011

one other thing - you mentioned HVAC gets air from the returns - is that 100% true, or does some air for conditioned air enter directly into the unit then become circulated in the house? The returns are in a completely different room. The HVAC and HWH would still presumably have some kind of suction since they are gas and burning air. But in those cases - I wonder if that's enough suction to "suck" sewer air from 9 feet away out a 3 square inch gap in the top of the drain in question. Even if it did - I suppose it would be burned and sent out my exhaust. There will be ample combustion air in the room.

Thanks,
Dan

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TheEplumber

· #6 · Apr 26, 2011

Google trap primer. Put one on the drain. This will solve your dry trap problem. Don't seal the pipe closed. You won't have gas issues with the primer installed

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Wildie

· #7 · Apr 26, 2011

denemante said:
Once drywall is up - I'll have no way to reach this pipe to manually pour water into it. The only source would be AC overflow and the HWH. The plumber didn't say I should only use that release valve only about twice per year - he said I should do it anytime I think the trap is dry. Is that ill-advised?

My only other choice is to run my own PVC to that drain pipe in question so I can access it from a few feet away.

I think that it would be a mistake to bury the drain behind the drywall. There will be times when maintenance will be required and having it hidden away is asking for trouble.
Hinged panel doors are available to allow maintenance on utilities.

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