Chimney Fire - Is it Possible with a Selaed Insert?

[Creamer]

I am very aware of chimney fires and the damage they can cause and keep my chimney very clean and check it annually. But I got to thinking - a chimney fire is usually caused by having combustible material (usually creosote) built up in the chimney that when a hot fire gets going ignites this combustible material to the point and the resulting fire can get so hot that it causes damage to both the chimney and the surrounding structure can can even ignite the rest of the structure. But can this happen if you have a well-sealed fireplace insert that only allows so much air to pass?

The fire, in order to get hot enough to do damage, has to have a supply of oxygen which due to draft normally comes through the fireplace. With an open fireplace there is a virtually unlimited amount of air available for the fire. But if the fireplace has an insert that is well sealed and therefore the amount of air to the chimney is limited can you get a damaging fire? Can the air "loop" down the chimney to the fire and back out?

I realize these are very critical "ifs" but I was curious as to other people's thoughts on this that are more experienced than I.

 

[oosik]

I had a chimney fire in the wood stove at our cabin in Alaska. I let things get too hot and the little bit of creosote ignited. It was as tight a system as I could make it. Double wall SS pipe, taped at each joint - only air going into the system would come thru the stove. I knew a problem was coming - the stove started making noises - wumpa - wumpa - wumpa. It was attempting to pull additional air thru the stove grating or down thru the chimney. I closed off the input air grating on the front of the stove and the chimney damper. The stove smoked a lot - filled the cabin with choking clouds of smoke - but the fire went out and all was OK.

After that experience I did two things - *) didn't load the stove so full of wood and +*) put a chimney thermometer on the chimney. Never experienced a second chimney fire.

What truly surprised me - the hot stove/fire was attempting to pull air back down the chimney. A fireman friend indicated this was part of what the wumpa - wumpa sound was all about. Fortunately the chimney damper cut that avenue off - but also caused all the smoke to exit into the cabin. A lot of smoke is better than having your cabin burn down.

Actually - being a little more observant/careful with your wood fires is a LOT better than any of the above.

And to answer your question Creamer - I would have to say yes. A chimney fire is possible with almost any system that burns organic material and can leave deposits of creosote. Correct design - proper installation - correct operation and proper maintenance will certainly reduce this problem.

 

[Deere Dude]

I have an air tight insert and clean my stacks out yearly.
I generally get .5 dustpan of dust and very small klinkers from the stack. My fireplace can only get so much draft that I had piped in so if I see the fire starting to get to hot I will damper the air down and that kind of smothers the flame down. But if I burn a lot of small fires, damp, light or dirty wood for a while, creosote or whatever stuff will accumulate
in the stack. It has to.

Then if you get a very hot fire, and you still can with any draft,that will climb the chimney and burn it out, start a house fire, or maybe warp the fireplace. Then you have a mess.

I have had my fires white hot already and I get very nervous and try to damper it down before anything drastic happens.

 

[KennyG]

The normal reaction to a chimney fire is to shut down the damper to choke off the fire. This should work but, although I burn only very dry wood and keep the chimney clean, I keep a chimney fire suppressant bag beside the stove to throw in if I every get a fire. I think it's the most sure way to shut it down.

 

[Creamer]

The normal reaction to a chimney fire is to shut down the damper to choke off the fire. This should work but, although I burn only very dry wood and keep the chimney clean, I keep a chimney fire suppressant bag beside the stove to throw in if I every get a fire. I think it's the most sure way to shut it down.

I have the same - a suppressant bag near the fireplace insert just in case.

I find Oosik's comments very interesting that the air will get drawn in from the top and feed the fire. It makes sense that it reverses the air flow. How tall was the chimney?

 

[6thgpSF]

so where do you get this suppressant bag?...russ

 

[oosik]

Not heard of "suppressant bags" however - a good 'ol 10 pound ABC extinguisher should do the trick. I've also heard that you can throw a tight woven wool blanket (old army blanket) in the stove and that will smother the fire. The smoke from cutting off the air supply created smoke that would choke a camel - I can imagine what a burning wool blanket would add to the calamity.

 

[bigdeano]

I had a chimney fire at a previous house. After a few seconds of panic I climbed up on the roof and dumped a glass of water down the chimney. Put it right out.

 

[Creamer]

You can purchase chimney fire suppressants from various places from Menards, Rural King or other box stores to specialty chimney and fireplace stores or online at places like Northland. Basically it is a log or bag that when heated in the fire rapidly releases CO2. It is better than a fire extinguisher because you put it in the fireplace or stove and then shut it so the only place for the Co2 to go is up the chimney and pushing out the oxygen.

 

[goeduck]

I just swept my flue yesterday, I try to do it twice a burning season. I am now in a one story house with a SS flue liner. About 18 of straight flue since it is an insert sitting directly under the masonary chimney. Pretty easy. I then clean the ashes out at the same time.

For some reason my flue does not build up much but I do get a build up on the bottom (inside) of the flue cap. Have not figured that out yet.