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.

 

[Wagtail]

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.

Interesting... I'll have to look into that before (my) wood-heating season starts.

I've always kept a dry chem fire extinguisher by the heater (and in the kitchen, and in the ute, and in the workshop, and on the tractor... I blame my pedantic Navy training) but CO2 would work great.

Oh, and oosik's "wumpa-wumpa" description is very accurate. :thumbsup: Happens with a blocked chimney too. (Scares the living CRAP out of you when it happens!!!)

 

[Erik M]

A dry chemical fire extinguisher fired into the stove will work for sure, but I have a 3 gal bucket full of the dry chemical material in the basement beside the wood furnace and if I ever needed to shut things down a few shovel fulls tossed into the furnace would do it.

Best way to avoid a chimney fire is to clean your chimney at least annually and burn only seasoned dry hardwood.

 

[s219]

We keep a couple of these around:

www.chimfex.us

They are started up like a road flare and then just toss in the fireplace. They are rated highly. I have no idea how well they work, and hope to never find out!

I remember having a couple chimney fires growing up and it sounded like a freight train. We later found out that the cleanout area at the bottom of the chimney was open between both sides (one for oil furnace, other for wood stove) which made it a challenge to put out the chimney fire because it was able to draw air from the second chimney.

 

[square1]

Not heard of "suppressant bags" however - a good 'ol 10 pound ABC extinguisher should do the trick.

Just be sure to pull the pin before throwing it in the fire

 

[Creamer]

Just be sure to pull the pin before throwing it in the fire

that is what the local fire department uses and they say they work well.

 

[PILOON]

I have done a lot of renovation work with some chimney experience.
I have observed that on the sectional 'screwed together' chimney sections that are very common sometimes were creosote caked in a weird fashion.
At some seams or joints there existed a washer like ring of creosote.
I determined it was from ingestion of cold air via the seam that caused the creosote to harden, in some cases an 8" flue might be restricted down to 4-5".
Being a thin cake of creosote deposit it would then be very easy for a subsequent hot fire to ignite that 'washer'. For that reason I always taped all the seams on adjoining sections of flue pipe with aluminum tape.
A bead of quality caulk over the exposed gap would also work.

 

[Creamer]

I have done a lot of renovation work with some chimney experience.
I have observed that on the sectional 'screwed together' chimney sections that are very common sometimes were creosote caked in a weird fashion.
At some seams or joints there existed a washer like ring of creosote.
I determined it was from ingestion of cold air via the seam that caused the creosote to harden, in some cases an 8" flue might be restricted down to 4-5".
Being a thin cake of creosote deposit it would then be very easy for a subsequent hot fire to ignite that 'washer'. For that reason I always taped all the seams on adjoining sections of flue pipe with aluminum tape.
A bead of quality caulk over the exposed gap would also work.

Interesting. I have never heard of doing that but it makes sense that a small cold air leak would cause a buildup. thanks!

 

[Deere Dude]

No exp. with chimney fires as I keep it fairly clean, but what does a guy do if he has one and throws some suppression material in it. I really doubt it will knock all the flames out so how would a guy deal with hot burning logs at that time. Just leave it and hope it all goes out then take care of it???

 

[oosik]

Well - in my one and only experience with a chimney fire. I had very heavy duty gauntleted leather gloves. When things sort of calmed down - a lot of the smoke had cleared out of the cabin - before the smoldering wood caught on fire again - I reached in and grabbed the logs - one in each hand and threw them off the porch - out into the snow. As I remember it took three trips.

 

[TnAndy]

We keep a couple of these around:

www.chimfex.us

They are started up like a road flare and then just toss in the fireplace. They are rated highly. I have no idea how well they work, and hope to never find out!

I remember having a couple chimney fires growing up and it sounded like a freight train. We later found out that the cleanout area at the bottom of the chimney was open between both sides (one for oil furnace, other for wood stove) which made it a challenge to put out the chimney fire because it was able to draw air from the second chimney.

We do the same, and too have never used them. My set up for each wood stove around the place (we have 3 in the house, one in the shop and one in a greenhouse) is like this: Fire extinguisher and Chimfex 'flares'.

They look like oversized road flares:

Then I keep a large Halon gas extinguisher in a kitchen broom cabinet for any grease/electrical fire in the kitchen area....no white powder to clean up in addition to any fire damage.