Please help. Sewer gas smell only at night, only January-March

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toughproblem

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Hello all,

First, I'd like to say that I am now working with a professional plumber and am willing to pay to solve this problem, but I could really use your thoughts and or suggestions.

Infrastructure:
City sewer
City water
Natural gas forced air furnance
Natural gas hot water heater

Problem Description:
In the evenings, I have been fighting a sour smell in my basement for the last three winters, which I presume to be some type of sewer gas. The strange part about this smell is that it is only present under the following conditions:

1) Cold night, Mid January to Mid-to-late March. 20 degrees F or colder
2) Night time, starting around 7PM and it is usually gone by morning
3) It is strongest is the basement, and sometimes permeates to the main floor as I have an open stairwell from the basement to the main floor
4) Rarely, when it is really bad, the smell will permeate to the main floor bathroom (through the walls?)

I have not been able to identify the source, and here is what I have done thus far to troubleshoot it.

1) Both floor drains have water in them
2) Basement sink drain p-trap has water in it
3) Basement toilet flushed regularly
4) P-trap for forced-air furnace has water in it
5) P-trap and clean-out cap for forced-air furnace is "tight/sealed"
6) Clean-out caps for all visible drains / etc are sealed
7) Roof vent is clean and not frozen
8) Professional plumber visited during the day when no smell was present with gas meter thing, was not able to identify source
9) Tried turning gas hot water heater off for a night, including turning off the source valve
10) Tried turning gas forced air furnace off for a separate night
11) Tried keeping the basement warm by opening all ducting vents
12) Tried keeping the basement cold by closing all ducting vents
13) All sinks / toilets / showers / tubs / washing machine / etc run regularly to ensure there are no dry traps

I am asking the plumber to visit during the evening when the smell is present, and hope to have this done this week.

At this point, I am willing to try anything and everything.

Please share your ideas!

Thank you.
 
Odors can be a troublesome problem to find.
Dead animal in the wall?
Cracked or broken vent inside wall or below floor.

Thank you very much for the suggested threads, I will go read them.

I don't suspect it's a dead animal since one would think that would smell year round, as well as more than from 7PM-7AM on cold nights.

The cracked or broken vent is an interesting idea. Could smell permeate from a cracked or broken vent inside poured concrete (basement floor)?
 
ask your plumber to check the water heater and heating unit vents, make sure they are drafting properly.

is it a funky egg rotten smell or a bad fart smell ?

funky egg is the w/h anode.

Will do, thank you. We think it is a bad fart smell.

If it were a venting/drafting issue, wouldn't it be producing this smell 24/7 rather than only at night?

Or are you thinking that the furnace runs longer and harder after dark and it could be contributing to the problem?

The thing that makes me skeptical about this is on one night I turned the water heater off (left furnance on) and it still smelled, then a different night I turned the furnace off (left water heater on) and it still smelled.
 
your waher machine. front load or top loader ?

the new front loaders have a stinky problem, trapped water sours

Top loader, and the washer is on the main floor. Does not appear to be the source of the problem.
 
well, ****, thats all i got, only thing left, take the garbage out and jump in the shower

It makes me want to considering moving. :(

Thank you for the help, though! I'm going to suggest the smoke-bomb route to my plumber tomorrow.
 
I should have mentioned this initially:

One of the floordrains near the hot water heater and furnace has a side plug thing that would not seat correctly, so I fit it as best I could and siliconed around it.

Do you think the smell could be permeating through the silicone?

​Thank you very much for the help.
 
personally, i think its the ac drain...they tend to stank during the winter mths.

but you have said, that all ptraps are full of water. yes, if you have a trap with a primer hole jerry rigged...that may be it

Hrm, there's something I had not considered. I attached a picture of the two lines from my outside air conditioner going into my furnace. Is one of them the drain line you are referring to?

I also attached a picture of the siliconed hole - when I initially discovered it loose I tried to screw it in using the threads but the trap threads seemed stripped, which lead to the siliconing.

AC.jpg

Trap.jpg
 
if that lil cpvc condensate ptrap evaporates. and the trap it drains into evaporates

the stank will come up that pipe into the house.

also...is the ac drain pan holding water ? it will become stagnant also

that looks like 1/2'' cpvc. minimum drain size is 3/4..they clog up
 
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if that lil cpvc condensate ptrap evaporates. and the trap it drains into evaporates

the stank will come up that pipe into the house.

also...is the ac drain pan holding water ? it will become stagnant also

that looks like 1/2'' cpvc. minimum drain size is 3/4..they clog up

That condensate pipe drains water when the furnace runs into the ptrap and I have verified that the ptrap has water in it.
 
ok..your op said stank between january and march

that is generally the mths the AC is not running and the trap dries out.

a heat unit does not condensate, only AC does

i think the stank has something to do with your ac/heat unit

because of the jan/march comment
 
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