Q&A / 

Sewer Smell When Using Fireplace

Tom Grote, who lives in Ivoryton, CT, has an unpleasant experience when he starts a fire in his fireplace. It's not a smoking issue, it's a sewer smell. Read what he sent me:

"I live in a two-story colonial with a bathroom and fireplace on the first floor.

Every time I have a fire in the fireplace, I smell a methane/sewer-like odor coming from my downstairs toilet.

This ONLY happens when I have a fire in the fireplace. I do not smell anything when I am not having a fire.

I have read your posts regarding dried up fixture traps and debris in drain vent pipes at the roof, but I only have this problem when I have a fire going.  I've had chimney experts and plumbers out to diagnose the issue but no one can figure it out.

Any insight into the problem would be helpful.  Thank you!"

Well Tom, I'm wondering why the plumbers you brought in didn't simply install a new wax gasket on that toilet. That's a partial fix to the issue, but you really need something else to solve the problem. I explain it all below.

Here's the issue, and I've written about it on my website before.

When you have a fire going, just look at the volume of air / gas / smoke that's billowing from the top of the chimney. It's probably hundreds, if not thousands, of cubic feet of air per MINUTE when the fire is really raging.

For every foot of air going up the chimney, you need to replace it in REAL TIME with an equal amount of air.

If your home is well sealed, the fireplace starts to get the air anyplace it can as nature abhors a vacuum. In your case, the air is coming back in from your plumbing system.

This is a very dangerous situation because you could be also introducing carbon monoxide into your home at the same time. If you have a fire going while your gas furnace or gas water heater (I assume you have this - if not you, others might) is operating, the suction from the fireplace can cause NEGATIVE drafting down the appliance chimneys and exhaust gas comes backwards into your home.

You should install a fresh-air intake vent hood system at the very least to try to solve this problem. In the SHORT term, I'd simply crack open a window in the room where the fireplace is to see if this solves the sewer gas problem. It should solve it instantly. If you do still have the sewer gas problem, then open the window in the fireplace room wider as a TEST.

You want the makeup air supplying the fireplace to be as close to the fireplace as possible. 

Watch this video to see how Tim SOLVED a problem in minutes!

CLICK here to contact Tim to help solve your problem.


6 Responses to Sewer Smell When Using Fireplace

  1. Thousands of cubic feet of air per minute possibly going up the chimney. So if, for example, it was 2,400 cubic feet, that would be (if my math is correct) 40 cubic feet per second. Seems like an incredibly powerful (and, to me, implausible) rate.

  2. Another major concern for this is that sewer gas can be flammable. If the fireplace vacuum pulls enough methane up from the sewer, it could flash ignite. Not super likely, but it is possible.

    The first and easiest thing to look for is a dried up drain trap. The first ones to check will be be the drains in a rarely used guest bathroom, or a floor drain in the basement. The simple (temporary) solution is to pour water down them to fill the trap and block the sewer gas from coming up.

    I say temporary solution because you still have to fix the ventilation issue ASAP in your home to ensure you're not sucking dangerous fumes from the other sources, as Tim mentioned in the article.

    Aah, the joys of home ownership:-). Good luck solving your issue and stay safe!

  3. Tim

    My last look at the IRC (Residential Code) was in the late 90's. At that time the combustion air opening requirement was 6 square inches and and located within 24" of the fireplace opening. As that code went unrevised since the mid 70's it should be accurate for homes built during that time.
    Currently ASHRE 90.1 has more stringent air leasee next

  4. Reminds me of an experience years ago when we first moved into our house. The house built in 1945 has a fireplace in the living room and one in the basement family room. We couldn't wait for the first cold night to make a roaring fire in the living room fire place and curl up with a bottle of wine. The "perfect" roaring fire and hot air up the chimney created a draft right back down the basement fireplace flue filling the basement up with smoke, lots of smoke!! Oh the romance of a fireplace!

  5. Tom, are you related to the late Jim Grote, one of America's great volunteer fireman? Since I know Ivoryton well, my first question is what is the age of your home. Tim, Ivoryton (name comes from making piano keys) has a selection of houses that range from shelter for the British to something built yesterday. My former house in Ivoryton was built in 1991. My current house in a nearby town was built in 1846. Unfortunately, so many of the old houses have been resided with Vynal siding as are all of the new homes. Add to the siding the Tyvek wrap. The windows and doors have weatherproofed and sealed to the point that the only source of outside air is the a/c. Most homes have septic systems versus hookup to sewers. My investigation would begin with checking if the septic tank needs a pump out. At the same time, make sure that main line to the tank is vented properly. Next comes the question of how many toilets and sinks are in the house. For every drain, there is a trap. Every trap needs a reservoir of water in order to prevent back flow of sewer gas. Lack of use means the traps can dry out. If air is pulled out of the house by a fireplace, the vacuum will be filled with air from someplace to include the sewer gas from the septic. The new homes are so tight that airflow becomes a real issue.

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