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

[toughproblem]

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.

 

[Smooky]

Sometimes air can be sucked in where it is supposed to be venting out. So are any of the exhaust vents such as from bathroom fans or the gas hot water heater or gas furnace close to sewer vents?
Do you have a wood stove that you burn at night or anytime? Do you have an outside air intake? Are your air filters clean on the furnace?

 

[Sponsor]

 

[toughproblem]

Sometimes air can be sucked in where it is supposed to be venting out. So are any of the exhaust vents such as from bathroom fans or the gas hot water heater or gas furnace close to sewer vents?
Do you have a wood stove that you burn at night or anytime? Do you have an outside air intake? Are your air filters clean on the furnace?

No, there are not any exhaust vents close to the sewer vents, the sewer vent is on the roof and the remainder of the vents are on the side of the house.

No, we do not have a wood stove. No we do not have an outside air intake. Yes, the air filter is clean on the furnace, I replace it every 6 months.

Thank you for the help!

 

[Jadziedzic]

Are you familiar with the smell of propane? If so, does the odor resemble the smell of propane?

 

[Standardairconditioner]

The reason this is worse in the winter is because the environment air is dry, so the dense humidity from sewage is more concentrated and evident. This is why you see city street sewers in New York City smoke humidity in the winters.

Your problem is a common one in Canada, where cast iron pipes were used in homes built in the 50s.

All your traps are filled, but the smell isn't coming from there.

The smell is coming from the vertical vent pipes, there is a crack and rupture in either the main one of the thinner auxillary one.

It may also be a disconnection of the lead calking at the no-hub couplers, easy to happen if the lower pipe is room temperature and the top pipe in the attics is exposed to frigid winters, the temperature difference does shock the coupler.

This problem is further amplified if you have a burning furnance, so it is consuming air and sucking in air from your leaking vent pipes.

The reason why the smell is more noticable in the basement, is because the sewage gases are heavier, and can concentrate on the basement floor and just stay there, stagnant.

Regardless who does the job, the cast iron vertical must be completely removed and replaced with current abs or pvc. If you are lucky, you can cut the pipe in the attic, and drop it down from the basement.

Even if you locate the damaged section, replacing just that is merely a band-aid for the iron rot to take damage elsewhere in the years to follow.

 

[toughproblem]

Are you familiar with the smell of propane? If so, does the odor resemble the smell of propane?

Yes I am, and no it does not. Thank you!

 

[toughproblem]

The reason this is worse in the winter is because the environment air is dry, so the dense humidity from sewage is more concentrated and evident. This is why you see city street sewers in New York City smoke humidity in the winters.

Your problem is a common one in Canada, where cast iron pipes were used in homes built in the 50s.

All your traps are filled, but the smell isn't coming from there.

The smell is coming from the vertical vent pipes, there is a crack and rupture in either the main one of the thinner auxillary one.

It may also be a disconnection of the lead calking at the no-hub couplers, easy to happen if the lower pipe is room temperature and the top pipe in the attics is exposed to frigid winters, the temperature difference does shock the coupler.

This problem is further amplified if you have a burning furnance, so it is consuming air and sucking in air from your leaking vent pipes.

The reason why the smell is more noticable in the basement, is because the sewage gases are heavier, and can concentrate on the basement floor and just stay there, stagnant.

Regardless who does the job, the cast iron vertical must be completely removed and replaced with current abs or pvc. If you are lucky, you can cut the pipe in the attic, and drop it down from the basement.

Even if you locate the damaged section, replacing just that is merely a band-aid for the iron rot to take damage elsewhere in the years to follow.

Thank you very much for the insight. The home is ~12 years old and does not have a cast iron vent pipe.

What is the best way to troubleshoot a potential rupture in the vertical vent pipe?

 

[toughproblem]

I did have a troublesome side plug on one of my floor drains, so I seated it as best I could and siliconed around it. I attached a picture of the sealed plug, do you think this could be the issue?

 

[Reach4]

What is that picture showing? OK... I am now thinking that is a closeup looking into the drain, and the whole photo only covers about a 4 to 6 inch square

 

[toughproblem]

Sorry Reach4, I should have described the picture better. That is a close-up picture of a floor drain, with a side port.

The open hole is the floor drain with water sitting in it. The side plug is my attempt at sealing the PVC plug with silicone after it would not seat correctly.

 

[Reach4]

Yeah, I came to that realization and did my edit while you were posting your enhanced description. Sorry.

 

[Widgit Maker]

sour smell in my basement

Suggestion,
If you can, go up on your roof and sniff your vent pipe to confirm that the odor you have is sewer gas. To describe sewer gas as a sour smell seems a bit unusual.

 

[toughproblem]

Update: I managed to trim down a 2" wing-nut style mechanical test plug and get what feels like a tight seal on the side plug. I opened the windows for an hour to make sure everything was aired out. Tonight will be a good test as it's around 9F outside right now.

 

[toughproblem]

Update: The main floor washing machine drain did not have a p-trap on it, we found that out by issuing a smoke test, and the entire laundry system filled with smoke. We cut away the drywall to verify there was no p-trap and added a p-trap.

The side-plug (cleanout plug) in the basement floor drain near the furnace was leaking smoke. We replaced it with a galvanized plug with teflon and paste, and then siliconed around it.

Unfortunately the weather is getting warmer so I'm unsure if I'll be able to verify it's fixed until next January. We will see.

 

[Growler]

If you occasionally or constantly smell sewer gas around your home on the outside, the odor is coming from your plumbing vents. Normally the wind will carry away the funk. If conditions are right, weather/wind/humidity, land slope, will carry that stink to the ground and spoil the party. Depending on the size of your house, you'll have 1 or more plumbing vents. VentGenie Filters builds an activated carbon filter that solves this problem immediately, guaranteed. Visit VentGenieFilters.com.

 

[Michael Young]

you haven't identified the source of the odor. at this point, it is only an assumption that it's the plumbing.

A couple of thoughts. Do you have any lonely forgotten floor drains where you could have lost the trap seal? Have you tried renting/buying a decent ozone generator. Ozone generators will neutralize smells. So if there is something other than plumbing down there (mold). An ozone generator will kill it.