Chimney fires

[Welderman85]

Just a dumb question on the subject because im kinda paranoid lol. What is the best way to prevent them and how common are they. I'm very new to the wood burning scene. And just want to be as safe as I can. How often should i sweep the liner?

 

[kborndale]

Dry wood is the most important thing......that means cut split and stacked for a minimum of a year (many types of hardwood can take up to 3 years to dry) With good wood you can safely sweep once a year.

 

[vwmike]

Some setups make more creosote than others. Brick chimneys are the worst as they stay the coldest. I'm amazed how little buildup i get with my summit on a class A chimney.

 

[Grizzerbear]

Dry wood would be the main way to prevent excessive creosote and also not smouldering loads that cause cool chimney temps. Good dry wood makes the latter a lot harder to do and is your best solution for clean safe chimney. I also clean my chimney mid season and end of season and then inspect it at beginning of season....my chimney has always been pretty clean but I have a wife, two kids and another on the way so that is my reason for going overkill on inspecting regularly.

 

[Sawset]

Lots of reading available.

 

[Zack R]

- Dry wood
- Hot fires
- Good chimney design
- Frequent inspection and cleaning

I hear they are more common than we think, that they can happen without the user even knowing. Not all chimney fires are as dramatic as the ones you see on video.

 

[begreen]

Chimney fires happen when an excess of stage 3 creosote accumulates in the chimney (or stove pipe) over time and then is ignited by high temps in the flue system. A typical scenario is one where creosote has accumulated over weeks due to poorly seasoned wood being burned or smoldering fires keep the flue temp too low. Creosote starts condensing on the flue walls when the flue gas temp falls below around 230º F. Then when something raises the flue temp to 1000º the caked-on creosote ignites causing a chimney fire. That something can be a load of dry kindling, accidentally forgetting to close down the air or using the stove as a trash burner.

With a modern stove burning dry wood, a flue staying over 250º and proper stove operation, chimney fires are rare.

Brick chimneys are the worst as they stay the coldest.

"Exterior" brick chimneys. Interior brick chimneys are at room temperature. "Chimneys belong in the house." - woodheat.org

 

[thrifty]

I have a clay tile lined exterior brick chimney with an uninsulated 6 inch stainless flex liner. I burn about 2 cords a year. It gets cleaned 4 times from the top down per 7 month heating season. The creosote lands on a piece of paper on the baffle and looks like approx. 2 cups of light fluffy powder per cleaning. If I do have a chimney fire it won't have much fuel to feed it. It's been 15 years now, no disaster yet.

 

[jetsam]

Sweep it every couple weeks if you are worried. When you see that you're wasting your time because nothing is coming out, you can back off to a more relaxed schedule. Most people wind up at 1-3 times a year. I usually do 3 or 4.

There's nothing wrong with doing it more often to get a feel for it.

Bear in mind that flue crud doesn't accumulate at a constant rate- it gets worse when the weather warms up because you burn lower, and it gets worse when you put wetter wood in the stove. Anything that lowers flue temperatures raises creosote accumulation.

 

[Woody Stover]

I have an exterior masonry chimney with 16' insulated 6" flex liner. Most of the flaky creo is above the roof line where the masonry is exposed on all four sides, and it's always looked cleaner below that when I look down with a flashlight. I figure that flaky stuff at the top probably isn't going to catch but I guess it could, in the exceptional conditions begreen listed. Wiser to play it safe, for sure. I get maybe 1.5 quarts, mainly from the top, when I sweep once a year.

 

[begreen]

For comparison, we annually get about 1/2 cup of soot burning 3 cords a year, interior metal chimney. Many years back we had to burn some damp maple. The chimney dirtied up after a month of burning. Had to clean it in late November and got about 3 cups of crud.

 

[bholler]

Chimney fires are more common than people think. But most are very minor and pose very little risk. But chances are of you heat with wood eventually you will have one. With dry wood proper burning technique's proper maintenance and a good chimney setup there will be very little fuel so it won't be severe and the chimney will donuts job of protecting your house.

 

[begreen]

With dry wood proper burning technique's proper maintenance and a good chimney setup there will be very little fuel so it won't be severe and the chimney will donuts job of protecting your house.

I want my chimney to start making donuts. That would be awesome.
(silly spellcheck fun)

 

[bholler]

I want my chimney to start making donuts. That would be awesome.
(silly spellcheck fun)

Oops I should fix that but it's funny so I wont

 

[Woody Stover]

chimney will donuts job of protecting your house.

With no punctuation or caps, your posts can be a challenge to read but I think what you're saying here is that you will do an even better job of protecting a client's house if payment includes cash and donuts.

I want my chimney to start making donuts.

Hickory-smoked donuts. Mmmm..

 

[blacktail]

I want my chimney to start making donuts. That would be awesome.
(silly spellcheck fun)

I'm burning mostly big leaf maple this year. How long before my chimney makes maple bars?

 

[firefighterjake]

Just a dumb question on the subject because im kinda paranoid lol. What is the best way to prevent them and how common are they. I'm very new to the wood burning scene. And just want to be as safe as I can. How often should i sweep the liner?

A. Burn seasoned wood . . . truly seasoned wood . . . not wood that a seller claims is seasoned or wood you think may be seasoned.

B. Burn at the proper temps . . . burn in the Goldilocks Zone. Not too cool so that you're producing creosote, but not so hot that it will ignite any creosote build up in the chimney.

C. Frequently inspect the chimney and clean when necessary . . . I recommend sweeping at a quarter inch build up.

As for how common . . . depends on a lot of factors. Here in Maine where a lot of folks burn wood for heat, many of whom still are burning in old woodstoves and using out dated thinking (i.e. cutting, splitting and stacking in the summer and burning in the Fall) and many of whom seem reluctant to check and clean their chimney we see a fair number of chimney fires (and Murphy's Law has the home owner calling us at 1 in the morning, in middle of a blizzard to fight a chimney fire on a wicked pitched metal roof.

I've also seen that heating oil/propane prices tend to have an effect on the number of chimney fires. Higher heating oil prices = more folks burning wood vs. lower oil prices = more reliance on the dinosaur burners.

 

[Woody Stover]

I'm burning mostly big leaf maple this year. How long before my chimney makes maple bars?

A pretty long time, if it takes 'X' BTUs to make one maple bar. Hope you are there all day to keep tossing in splits every few hrs.

 

[Sawset]

For arguments sake:

Burn seasoned wood . . . truly seasoned wood .

The first year here everything sizzled, and the first hour on a cold start was a struggle.

Burn at the proper temps

I had no flue probe. Stove top temps were never over 450f. Never. Couldn't understand how folks could talk about 4-600f. stove top being "normal".

Frequently inspect the chimney.

The whole thing early on made me nervous. I inspected once a month. Running a brush up, I realized my flues were bone dry and clean. I was relieved. And could be more confident about going forward with what I was doing. I burned hot, as in, it never smoldered, flames were active, very active with the quality wood that I had to work with. The wood was what it was, and I was ok with that. As long as I wasn't endangering myself or the equipment. Inspecting, and getting positive feedback verified what I wanted, with the idea - keep doing what I'm doing and improve where I can.

 

[Sawset]

I'm burning mostly big leaf maple this year. How long before my chimney makes maple bars?

At 50lb per load, 20% moisture, 3% sugar, it'll be a couple months before bars start forming. Get them on the next cleaning.

 

[Woody Stover]

At 50lb per load

I never saw the stuff but it sounds like lightweight wood. 50# might be like three loads.

 

[Welderman85]

Ok what's the difference between smoldering and letting a fire burn out. Also what a good way to check temps on a insert. Ad for the the maple and doughnuts. The a place buy me that makes me with maple syrup frosting and bacon on them. I'm hungry now lol

 

[Sawset]

Ok what's the difference between smoldering and letting a fire burn out.

Wood goes through, for the most part, a couple stages during pyrolysis. The main ones are, breakdown of the long chain molecules, lignin and cellulose, second the breakdown of mostly the remaining carbon.
The first, contains lots of impurities, creosote being one. It condenses at a temp of around 230, 250f. The second involves mostly carbon ( think charcoal brickets, burning clean and hot).
Flue temps above 250f (preferably higher) allow the first type unburned gasses to escape without condensing. Charcoal, contains mostly the orange glowing carbon (coals), and little in the way of creosote compounds that can condense. It can burn at any temp and still leave little residue. Allowing a stove to run it's course, reduce its load to coals, at that stage poses little danger of creating deposits in the flue.

 

[Woody Stover]

what a good way to check temps on a insert.

You can try putting a meter on the front of the box in different spots. On the Buck 91 I put it above the door, about where the top of the box hit the front. If you have an infrared thermometer, you can open the door and shoot the top of the box, and see how the actual temp relates to what you are seeing on the meter on the front of the stove.

 

[begreen]

This website has a lot of good information and tips on wood burning. The 3d video on this page - Efficient Wood Stove Operation, has some helpful tips.

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