Chimney odor in house

[Cold1313]

I've done a lot of reading and have not yet found a good solution to the "fireplace" smell that I get in the spring and now in the summer with the high humidity.

History: My 1969, ranch home has a clay 2 flue chimney. One flue for the gas water heater or furnace in the basement (no longer used for that purpose). Second flue is for the fire place. Ash traps extend to the basement floor on both. Fireplace and part of chimney has a large build up of glazed creosote from burning green wood I believe. Most of this was removed in the fireplace area last fall. I completed removed the firebrick for the fireplace up to and including the damper.

Brick was removed to install a Harmon pellet insert. SST flex pipe run out the top of the chimney. Pink fiberglass insulation was packed around the exhaust pipe to seal the chimney. Fresh air intake was dropped down into the ash cavity that extends into the basement. Pink fiberglass around that pipe to seal air from the basement. Pellet stove worked great over the winter.

With the other flue, I would vent a cheapo TSC wood stove into it, in the basement. Just by sticking the exhaust into the hole in the flue. Worked great for years. A friend gave me a used Harmon stove to replace that unit (assuming it would perform better) and it worked well the few times I used it over the winter. It sat for a month and then when I went to fire it up, I had smoke coming out of every twist lock joint on the stove. Nothing changed, never had this before. Put a match to the hole at the flue and it would draw the flame into the flue. Cannot figure that one out....yes, all pipes are clear, flue is clear - everything. After attempting to fire it up several times, with the same issue, I gave up (still never got back to tinkering with it) - got tired of stinking up the house.

My main issue is the odor from the fireplace in the house (not basement). We had hoped by removing all of that glazed creosote brick, the smell would be gone - especially with the insulation to help prevent down drafts but we still have the issue. I believe it is all downdraft issues as when it is humid out, or if the bathroom vent fans or dryer run - the smell starts / gets worse. Open a door to draw in more air and it backs off (not ideal right now with 95+ temps outside with 90%+ humidity).

Is there a better way to form a true seal around the flue and my pellet stove flex pipe? Or a way to ensure that I am drafting out the chimney instead of down? (Aside from spending thousands on an electric, draft fan for the top of the chimney.)

We don't half @$$ stuff when we do projects, so we were quite surprised to still get an odor around the fireplace this year. I know the fiberglass insulation will let some air by, however I am not aware of a tight sealing product that can withstand the temperatures. I.e. I can't foam the chimney, etc.

Edit: I should add that I am more concerned with addressing the odor when the vent fans and dryer aren't running. I understand I am creating a negative pressure when those turn on. Other than cracking a door or window, I'm not sure of an "automatic" fix for those... Just thought I should clarify that it's the "humid day and now the house smells" issue.

Thanks for the help!
-Matt
Northern Ohio

 

[johneh]

I could be way off coarse but it seems when you close up your house
for hot or cold weather you get into a genitive pressure situation . and to
compensate air is being drawn down the flue You must find some way to
equalize inside outside pressures suggest you open a window at each
end of house to start just a little and see how that works . If it does find a
more permanent solution
Just my nickles worth

 

[Cold1313]

It is an air pressure / balance issue. No issues in the winter with the heat running (not the pellet insert). Just when the heavy humid air comes in the spring and the a/c is on. Right now, I turned on the clothes dryer and the smell started creeping in - opened a window some and the smell is gone. So that makes sense. Now I need to find a way to keep the smell out when nothing is running. I don't want to draw air from the outside because that will be hot and humid.

 

[johneh]

Sounds like you have a tight home
Maybe to tight all homes need some air exchange
to keep us healthy . Personally I hate stale air so even
though I use A/C we keep a window in an unused room cracked
just for some air movement

 

[Cold1313]

Sounds like you have a tight home
Maybe to tight all homes need some air exchange
to keep us healthy . Personally I hate stale air so even
though I use A/C we keep a window in an unused room cracked
just for some air movement

It seems to act that way but given the age of the house ('68) and still using the original windows, I have major heat transfer in the winter. I'm proving things over the years but this odor has been consistent - actually it's worse now. With the fireplace, the glass doors helped keep the smell back a little better than the Harmon cover.

 

[Nigel459]

We experience the same in some of our outbuildings. Pretty sure it’s “reverse stack effect” and on hot humid days days can produce the worst odours.

The solution is to block the airflow. One we do from the bottom by effectively capping the connector pipe above the wood stove.

On a pellet stove install we simply cap the pipe outlet.

I understand blocking the air path may be more complicated in your situation with the masonry etc. Pink fibreglass is not airtight... I have seen chimney tops wrapped with plastic bags before... good luck

 

[Cold1313]

I can fabricate some sheet metal, if I can find the right material (caulk?) to seal against the flex pellet exhaust pipe.

 

[articcatbill]

Have always burned wood, we have a fireplace and pellet stove now. Have always tried to prevent that flue odor we get at times, same issues worse on damp and/or humid days. Keeping everything clean helps, but in our fireplace I find it impossible to stop completely. Our solution, burn a candle in the fireplace, we do not always have to burn it and after awhile it seems to help neutralize the odor, and it looks nice. Used to do that with our wood stove sometimes in the summer as well.

I am guessing with your pellet insert that this is not really a possibility, but just wanted to offer it up. After trying all different approaches this seems easiest and most effective for our fireplace.

 

[Cold1313]

Have always burned wood, we have a fireplace and pellet stove now. Have always tried to prevent that flue odor we get at times, same issues worse on damp and/or humid days. Keeping everything clean helps, but in our fireplace I find it impossible to stop completely. Our solution, burn a candle in the fireplace, we do not always have to burn it and after awhile it seems to help neutralize the odor, and it looks nice. Used to do that with our wood stove sometimes in the summer as well.

I am guessing with your pellet insert that this is not really a possibility, but just wanted to offer it up. After trying all different approaches this seems easiest and most effective for our fireplace.

Thank you for the feedback. I wouldn't be able to use the candle method, but I need to find a way to induce / force a draft upwards.