Mysterious smell, common ideas checked already...

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New Member
Dec 5, 2021
SE Michigan
Didn't see anything in my quick scan of the thread, but is this a 'single flue' chimney? ...only this one fireplace and no other flue's? It seems that once every couple years someone mentions burning a fireplace/stove and the smoke leaving that flue gets pulled back into an unused second flue (basement fireplace, gas appliances, etc) in the same chimney. That can often lead to a smoke smell indoors. Might also take a peek if you burn again and make sure the smoke isn't doing something weird like swirling around and getting pulled back in an attic vent or similar.

I also don't know how 'tuned' your nose is, but if you're burning something like oak/ash, etc and smell a pine/fir/other common framing lumber smoke smell, that would be a good time to throw on the brakes!
It has three flues: the middle larger one is the fireplace, one one side it is the exhaust for the water heater and the furnace and the third one is a dummy for aesthetics. I doubt the second flue is playing a role simply because the smell was localized to the living room where the the fireplace is. I also often go to the basement (where the furnace is) and I could not smell anything.

Out of curiosity, how can a fireplace cause a fire which is starting somewhere in the framing of the house? ( I am not asking about how the carpet can catch fire :p)


Minister of Fire
Nov 17, 2019
Long Island NY
It can do that by getting combustible parts hot...


Minister of Fire
Nov 19, 2005
If you're not getting any smell in the basement, then that is a good sign. But this type of 'shared chimney' situation is something to keep an eye on. When you're running the fireplace, it will be pulling quite a bit of air out of the house and up its flue. It's very easy to pull 'make up' air right back into the house through that second flue... especially if the water heater/furnace are not actively firing and creating their own draft.

As far as the fireplace causing a fire - over the years, we've seen all sorts of examples. Anything from shoddy original construction to bad modifications to cracking mortar/missing joints, etc. It has always seemed to me that there was somewhat of a transition period...20's, 30's, 40's 50's had hand-built fireplaces by masons who knew roughly what they were doing and likely expected the fireplace to be used with some regularity. 60's, 70's, 80's still had mainly hand-built fireplaces but they were becoming more aesthetic or maybe only used on Christmas, so I think a fair amount of sketchy construction could still pass. 90's onward, things went more pre-fab so while you could still get questionable installs, it was a lot harder to goof up.

Even in the 'best' design, there are still some relatively short pathways from the fire to the framing. Sometimes people like to snug the framing right up to the chimney, then you're only a cracked mortar joint away from fire.


'best' fireplace desigh.jpg


Minister of Fire
Nov 17, 2019
Long Island NY
^That. Those pics tell why there is a code with clearance requirements.


Staff member
Nov 18, 2005
South Puget Sound, WA
This is a fair point, my 5 minutes don't say much, I can't exclude momentary movements. Ultimately my goal of finding out the source is to eliminate or reduce it significantly. If we accept the idea of the smell being caused by contaminated air down the chimney (no matter the mechanism), what is the solution?
Somebody mentioned the inserts because they were unable to cope with the smell. Is this really the only way to eliminate it? I like the idea of a fireplace but I am not sure I would want to spend 2k+$ on an insert.
Stuffing old blankets up the damper would become quite messy after the first use and only closing the damper is obviously not enough.

Let me put this question differently: you guys are obviously using /have used a fireplace, do you also notice a lingering smell of smoke in the first one two days after the fire?
Has anyone run a camera down the flue to look for cracked tiles or missing mortar? If it is to remain a fireplace, and there are no serious safety factors like Corey mentioned, then a top of the chimney damper could be installed.
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Minister of Fire
Nov 8, 2011
North Central Idaho
What is your other source of heat? I know if my furnace kicks on while I'm using my stove it will back draft into the house.