education in chimney fires

I have a Tarm OT-50 and because it is not a gassification boiler it produces a descent amount of creosote. I've heard from most people that if you have a non gassification boiler it is inevitable that you will have a chimney fire at some point. I've been doing some reading about chimney fires and i have some questions that i'm hoping I can get answered so I can better understand how to run my boiler and avoid a chimney fire as much as possible.

1. What actually causes a chimney fire? Is it heat from overfiring the boiler or is it sparks that make their way up the chimney and get stuck in the creosote?

2. Can I still have a chimney fire if I don't overfire my boiler and i try to run it in the optimal temp range as much as possible?

3. I realize that it is the creosote that burns. I have noticed that there are two different forms. One is this black tar like sticky stuff that is just plain nasty. The other kind is puffy and crusty and flakes off easily. I've noticed that if you apply heat to the the black tarry shiny stuff it puffs up and becomes brittle and flakes off. Are both of these present in my chimney? If the sticky stuff is present in the chimney how am i supposed to remove it because that stuff does not just come off with a brush? How are both created? Is the sticky stuff what is created if you don't run your boiler up to the optimal burn temp and then when it gets to temp the sticky stuff burns off and it puffs up and blocks the chimney? The crusty puffy stuff doesn't appear to burn. I've put a torch to it and all it does is glow. If this stuff builds up in my chimney do I still have to worry about a chimney fire, or is the main concern the reduced draft and the plugged chimney?

4. I have a hard time seeing what my chimney looks like from the bottom, even with a light and a mirror in the clean out. Can i get an idea of what my chimney looks like by looking through my boiler and into the connecting stove pipe, or will the stove pipe build up creosote faster than the chimney? How much faster does the single wall stove pipe build up creosote compared to the chimney?

5. If i have a chimney fire, i know i need to close everything up tight to cut off the draft to the chimney. Does this mean I also need to prop shut the barometric damper too? Is propping it shut good enough, or should i cover the entire opening with something to make sure the draft is completely blocked?

6. From researching on the internet i found something called Chimfex. It claims it starves out the chimney fire in as little as 22 seconds. I found them at a local hardware store and bought one for $25. Does anyone have any other advise or suggestions for extinguishing a chimney fire? I know i've heard things like throwing chain down the chimney or spraying water down it, but both of those either destroy the house or the chimney. I'm looking for simple things that work but won't harm the chimney or house if thats possible.

7. I've noticed what seems to be quite a bit of build up of creosote in the boiler. I've only ever run a wood stove. The amount of creosote seems alarming to me, but i don't really know what i'm looking at. How much creosote is ok inside the boiler and how much is too much? Can this creosote catch fire just like it does in the chimney or do i not need to worry about that? Do i need to scrub the inside of the boiler just like i do the chimney? A lot of the stuff in the boiler is black and shiny and sticky, if it is needed, how do i remove that stuff?


Any other information people can give me would be much appreciated.

I have read the Tarm manual and it said pretty much the same thing about the fires. The best bet is to burn hot. If you can't burn hot then don't burn and use the oil. Tarm recommends using the oil in the spring and fall and only use wood when its cold. Hopefully in the next year or two I will have the money and resources to put in some storage. For now i have to deal with what i've got.

At my parents house when i was younger they had a chimney fire so i am familiar with what it sounds like. The big difference is that they have a vermont castings wood stove and their house is only 1 story so the distance from the thimble in the chimney to the top is probably only about 5 or 6 feet. The one or two times they had a chimney fire all they did was close everything up tight and the fire burned out in about 5 minutes. In my case the boiler is in the basement and the chimney is at least 20 feet tall. That is a lot more creosote and a lot more heat that will be produced. It is also more complicated in my situation because i have a boiler and not a wood stove and it is a wood oil combo. I want to be as cautious as possible, but i also don't want to go as far as being paranoid and create a lot of extra work for myself. That being said, it sounds like it would be difficult for me to over do it as far as prevention goes, especially if some of you are cleaning your chimneys once a week. The big thing I've noticed about my boiler is that it heats up a lot faster with the wood than with the oil. I also have to be careful because if i get too hot of a fire going and i get a good bed of coals the boiler can't absorb all that extra heat so it ends up dumping the heat. The best thing I've found so far is I wait till the boiler is down to about 155, just before the oil kicks in. Then split my wood up pretty small so each piece is no more than 3 or 4 inches in diameter and i light a good fire. It burns hot and fast and by the time the boiler is back up to temp there isn't much but a good bed of coals left. By that time i don't have to worry too much about creosote because any moisture is gone. Then it'll be about another 2 or 3 hours before i light another fire. On colder days like we just had here a couple days ago when it was about 15 during the day I can let the fire burn down to just coals and then it will sit for about an hour or so and there will still be some coals when i go to start the next fire to heat the boiler back up. I'm just a little paranoid because i know the boiler can produce a dangerous amount of creosote and the last thing i want to do is accidentally burn down my house.

I do realize that moisture is always there, but if the fire burns hot a clean doesn't it create less creosote because the moisture makes it all the way up the chimney instead of condensing on the inside of the chimney?

i have a brick chimney with 8 inch modular flue tiles. Until i put in this boiler it only had the exhaust from my oil boiler going up it. The last time i checked it, it was completely clean. The chimney was built in 1986 when the house was built. The chimney is on the gable end of the house so 3 sides of it are exposed. There is also a fireplace flue in the chimney. The fireplace does not get use on a regular basis. We only use it once in a while when its really cold because it only heats the living room and it messes with the thermostat so the rest of the house will get cold. For the most part the chimney is in good shape. The chimney was not capped until 2011. The first year that we had the house i noticed a lot of moisture coming down into the fireplace. I also noticed when we had a fire in the fireplace that i would get a back-draft and a puff of smoke into the house when the wind blew. I capped both of the flues in the chimney and haven't seen any problem with moisture or back-draft since. The last time i looked at the inside of the chimney everything looked solid and it looked clean.

The only thing i've noticed about my setup is that the draft seems a little slow. I think it might be that the basement is too tight. I think i might need to set something up to allow more air into the basement so there is more positive pressure in the basement. I noticed the other day when i had the bulkhead open that the fire was burning pretty good even with the damper mostly shut, but when i shut the bulkhead the fire died down some. It appears to me like the boiler might burn more efficiently with a better supply of combustion air.

My boiler (Tarm OT-50) has a flap in the top of it that can be adjusted. Straight up and down and it blocks off the top of the firebox so the flue gasses get sucked back through the hot coals and across some heat exchange tubes before going out the chimney. If i try to run it this way, even with the draft wide open my stack temps only reach about 150 on the outside, (I think that means about 300 on the inside). That isn't hot enough. So i moved the baffle at the top of the firebox so its at about 45 degrees. This allows more heat up the chimney and wastes some of the energy in the flue gasses but when running like this the flue temps get up to between 350 and 400 on the outside of my stovepipe (I think that would mean between 700 and 800 on the inside). I also noticed that if i ran with that baffle straight up and down i created a lot more creosote in the firebox. It was enough so i could see it dripping down the walls and it was the nasty shiny sticky stuff. After adjusting the baffle to a 45 everything seems to burn much cleaner and i only see a little bit of dry crusty stuff accumulating and it flakes off. on its own.

I was thinking that if i let more air into the basement it would allow for a greater draft and i might be able to run the boiler the way it was intended with the baffle straight but and down so i can burn the flue gasses too.

Fred61 said:

Sounds good! Just remember an outside chimney cools the exhaust faster so be sure to stay on top of your maintenance. I had two 34 foot tall chimneys, one on each end of my previous colonial and I had the mason insulate the flue tiles from the brick with 2 inches of vermiculite. Worked good!

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How did the mason do that? Was it expensive? Did it require rebuilding the chimney?

maple1 said:

I am on the opposite side of thought posted above re. barometric dampers.

I think one should be there.

They limit draft the appliance sees - and during the 17 years of using my old boiler, the primary potential source of a chimney fire igniting was from wind gusts sucking the fire out of the firebox up into the pipe & chimney. I'm on an open hilltop so maybe more vulnerable than others - but it was risky business if my damper happened to stick shut. Plus, if it is installed in the right place, it can also serve as a very handy inspection & cleanout point. Mine was (still is I guess) just before the flue T - I could peek in at the flue & see what was there, scrape/knock down/vacuum out the fuzzy stuff. Now I use it as a place to stick a vacuum hose in with sump pump hose stuck on the end to vacuum ash out. Just have to flip it open and you're in.

Keep in mind though that inspection needs to be regular & often - that point will likely be the place that sees the most build up. But it will be easy to get to & clean out.

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Ok, since someone brought this up I have some questions. I have heard that the damper puts cold air into the flue so it cools things down and this isn't always good for a wood burning setup. The guy that put in my system put my damper about 6 inches behind the boiler. Then there is about 2 feet to the chimney thimble. Is this a good setup, or should the barometric damper be further up the pipe?

I have a thermometer on the stovepipe so I have some idea how well i'm burning. It is just one that sticks on the outside because I have single wall pipe. I put it on the elbow right before it goes into the chimney. This is about 2 feet above the barometric damper. Is that a good place for it? Where it is now, when the fire is burning good i can get readings of up to 450 from the outside of the stovepipe. According to the thermometer that is in the optimal burning range. But of course that doesn't take into account the added cool air from the damper. So really the fire is burning hotter but the damper is cooling it down some. Should i move the Damper and then put the thermometer below the damper or is it better the way it is set up now? Is one way better or worse as far as creosote goes?

Currently I've been burning for about 2 weeks and There is a good layer of creosote on the inside of the stovepipe and the other day i noticed it had dripped down the backside of the damper and it was stuck. The stuff in the stovepipe is crusty, but the stuff on the backside of the damper is that nasty black tarry stuff. I'm sure that is because the damper door always has cool air going across it and cooling it way down.

I have to agree with you about the burning. As this is my first wood boiler it has been a learning experience for both me and my girlfriend. The first couple fires I had created a lot of creosote and made me a little nervous. Then I discovered that if i changed the position of the baffle at the top of the firebox i had a lot better combustion. Then beyond that I discovered if i split my wood down to pieces that were no more than 4 inches in diameter the fire would burn hotter faster. Then I figured out that the boiler held enough heat that I didn't need to keep a fire going all the time. I could set a good strong fire once every 2 or 3 hours. I also found that at night it worked out best if I threw in a couple sticks of wood to make the fire last a little longer, but not too much. Then I'll set my alarm for about 4 hours later and I'll get up and restart the fire and have a good strong burn and i'll thrown in a larger stick or two of wood to make it last till I get up. Doing this way I'm having hotter fires and there isn't as much smoldering because I'm not trying to make the fire last all night. After all this I'm not seeing too much new creosote. I am seeing a little bit of ash sticking to the old glassy sticky stuff, and I am seeing some of that stuff burn off, but not so much new creosote. The first day or two really made a mess of thing though. The first couple fires I had the inside of the stovepipe and the boiler were all glassy and sticky and you could see the creosote dripping down the walls of the firebox. A wood boiler is definitely much different than a wood stove because of the water and the cool walls.