Bad Chimney Smell Coming Into House

I'm hoping someone here can help me with a strong odor coming into our house from our chimney, through our Harman Mark III.

First, Our M3 was installed by the previous owner as a fireplace insert. I burnt coal steadily from October to May to heat our home in Northcentral PA. At the end of the season I thoroughly cleaned out the stove. We only burnt wood to get the stove going.

The chimney is approximately 25 feet tall, and has two separate flues, and we operate two separate coal stoves in the winter.

The chimney we are having the problem with is on the main level, it has a damper, and I have it closed. The problem we are having is with a strong odor, that smells a lot like Lebanon Bolonga or wet burnt wood embers, take your choice. It smells terrible. The only time we have this odor is on hot, humid days, which are plentiful in PA right now. The house is very well insulated, and we suspect this is adding to the problem, so we have cracked downstairs windows some, but the problem persists.

I'm pretty sure the house is so tight, that the air conditioner is pulling draft down the chimney. How can we stop this? And why is it that it will pull into the main area of the house, but won't pull in the basement?

Any help is GREATLY appreciated, as the odor is so strong it is bothering everyone. We have tried fireplace deodorant but it is NO WAY strong enough.

Tom

You will have to pull the stove and inspect and clean the chimney.

I suspect a dead animal.

My big chimney does this about twice per year. The basement is cool, and when conditions are right on a humid day the basement smells a little like creosote.

My air conditioner has a vent that you can open/close to make it recirculate air, or draw fresh air and push it into the house. Check yours to see if it has the same feature - a small adjustment may help.

put a cover over the top of the flue liner , stop the air flow. get some odor ban spray in the thimble or up the fireplace damper...dont forget to remove the cover in the fall...

I am also trying to figure out how to properly clean what Harman calls the "spiral chamber" -- the area above the firebox where the combustion fumes travel to get to the exhaust breech. There is quite a bit of flyash in there, and I can't sweep it out with my shop vac, simply not enough suction. I feel like I am at the point of pulling the entire insert apart, which is caulked in place.

I guess there is always a possibility there could be a dead animal in the chimney, but the smell is not constant - and doesn't smell dead. Honestly it smells like a musty, wet, creosote.

Our house has central AC... -- the one post had me thinking I could probably close any cold air return near the fireplace, and force the AC to draw harder from elsewhere... (?)

This smell is making my wife crazy, and well, you all know the situation from there... Solving this problem has been quickly moved up the priority list.

If the chimney has a steel liner, the combination of acid reaction with steel can also be strong.

I did call the Chimney Sweep. He is full scheduled until the end of NEXT month.

Sounds like you have two reasons to surgically remove some caulk.

1. to clean chimney base and inspect the rest of chimney.

2. to whack the fly-ash loose from around those spiro-tubes with a heavy rubber mallet or dead-blow hammer while vacuuming.

I have a three flue chimney, the two outside flues are oil boiler and the Axeman coal boiler. The center flue is the fireplace which is never used and dampered off. In low draft situations it is not uncommon to have a reverse draft in the chimney not being used. It can be cured with a baffle at the top..... but it's ugly.

Tell me about this baffle? You bought it or you fabricated it?

I didn't put one up because I didn't want to look at it. Just a piece of sheetmetal placed between the flues at the chimney top is all it is. The old pros did it with brick and a cap, just support the corners.

I put a big Nerf ball in ours in the chimney thimble in the basement. I even left the original plastic bag the ball comes in on it.

Those are both excellent ideas. Thank you.

Right, it happens on hot humid days. What's happening is on these hot days, the chimney is cooler. It cools the air that's in it and it descends, (draft reversal).

The best idea I've heard so far is sealing it from the top although it may not completely solve the problem, just ease it.

I see this happen with my chimney as well, I sealed mine at the bottom.