Smoke Smell in Basement

[KaiserRolls]

We bought a new (to us) house built in 1970 this summer and were excited to use the fireplace come winter. However, after using the fireplace 5 or 6 times, we've noticed our basement utility room directly beneath the fireplace gets an intense smoke smell about 15-45 minutes after lighting a fire. It's not visibly smoky / hazy - but you can absolutely smell smoke.

I've narrowed down to 2 possible issues but want opinions if i'm missing something.

Possible issue 1: Smoke is back drafting down the ash dump door due to negative pressure in the basement pulling smoke from the firebox to the basement. I did some temporary masonry caulk on the ash door to seal it up about 95% and still had smoke in the basement after lighting a fire to test. This leads me to believe this isn't the culprit.

Possible issue 2: (reference image) Smoke is coming out of the fireplace flue and getting sucked back down the appliance flue due to negative pressure in the basement - especially since the newer furnace is now direct vented out the side of the house. Furnace is not vented out of the flue anymore. Condensation on top of the hot water heater would validate the back draft / negative pressure / air coming back down. I'm thinking the old furnace + hot water heater used to cause enough pressure to get the air moving out and not allow the smoke from the fireplace to come back down.

Attached a visual to help give more context. Even though very rare - i'm leaning towards this being issue # 2.

 

[begreen]

The likely issue is that both flues terminate at the same height so that smoke from the fireplace is being siphoned down the basement flue. The solution is to put an extension on the fireplace flue.

Chimney Flue Extension | Chimney Extension Kit - Rockford Chimney

The Specialty Flue Extension will increase height and draft of your chimney and features an attached chimney cap. Easy to install and ships free.

www.rockfordchimneysupply.com

 

[KaiserRolls]

The likely issue is that both flues terminate at the same height so that smoke from the fireplace is being siphoned down the basement flue. The solution is to put an extension on the fireplace flue.

Chimney Flue Extension | Chimney Extension Kit - Rockford Chimney

The Specialty Flue Extension will increase height and draft of your chimney and features an attached chimney cap. Easy to install and ships free.

www.rockfordchimneysupply.com

Thank you for your input. I'm going to call a local chimney company to see when they can get out. I don't need to be messing around that far up.

 

[begreen]

Thank you for your input. I'm going to call a local chimney company to see when they can get out. I don't need to be messing around that far up.

That's wise. Hope it gets resolved quickly.

 

[gmant]

I'm experiencing the same thing with a new woodstove insert (Regency i3000) I put in, though we've also had it from traditional fires in our main floor fireplace causing smoke to come into the basement (via our basement woodstove insert liner). We already have an extension on the basement liner, which I expected to help, but it doesn't seem to. Did this fix work for you? If not, what other measures did you take? TIA

 

[begreen]

Shouldn't the extension have been put on the main floor chimney pipe?

 

[gmant]

Shouldn't the extension have been put on the main floor chimney pipe?

Thanks for the reply. I think in retrospect that probably would have been the default. But given that at the time (last year) we had the basement insert installed, we only had a traditional masonry fireplace and flue upstairs, there wasn't really a way to "extend that", so they opted to extend the one lined flue we had instead, basically for the sake of creating distance between the 2 smoke outlets. Given that both flues are now lined and easily extended, you believe that extending the main floor flue and removing the extension on the basement flue would make the most sense? I'd imagine that in windless conditions either attempt would result in some smoke getting sucked down. Are you hoping that the smoke is still hot enough that its rising will outpace any suck that the basement flue would produce? And, what would happen if we lit the basement insert, would that then cause smoke to get sucked into the main floor flue? Would love your thoughts!

 

[begreen]

If the basement has issues with negative pressure, say when an upstairs door is opened, or exhaust fan or clothes dryer is turned on, then there may be slight suction on that flue. Hot air and warm smoke tend to rise upward so if the basement flue is taller it still may suck in smoke. Whereas, if it is lower by 12-18" then it is less likely to.

 

[gmant]

Seems reasonable to me, I think it's at least worth a shot. I'll see if my chimney guys can switch the extension out. I did try opening some basement windows before lighting the upstairs insert today, and no smoke smell, which (in my inexperienced eyes) implies it is indeed a stack effect issue. To be fair, it was also a very windy afternoon, so might be spurious data. Thanks again for your input! I'll let you know how it goes