Chimney fires

[Scribner's Mountain Maple]

I am trying to finish up my season, scrounging wood where I can, and for some reason the wood i am using (slab, Pallets) is getting way too hot. I am using a king 4*12 w/ no blower. When I fill the fire box full full, I am getting a chimney fire almost every time. It sure makes it boil., but when the galvanized and stainless stack pieces go past red and become almost translucent, I get a little nervous and shut off air intake to kill the fire.

The question is what isn't happening in my firebox that is creating the creasoulte (sp?) build up in the stack? This build up is igniting when I put a large amount of dry wood in at once and a touch like flame is rocketing out of the stack. I would guess I saw stack temps into the 3-4000 + degree range last night before i cut off the air. I mean I know the answer is to do with the wood/gases not burning completely, but what can I do to prevent the build up in the chimney? and to get the gases to burn completely in my firebox?

[chevypower]

Is the wood seasoned and dry? If not that will make Creosote quickly. I'd like to see a picture of your flamethrower if you happend to take any of it, I'm surprised you have a stack left!

[northwoods_forestry]

Wow, sounds pretty darn scary. Are you sure it's creosote burning in the chimney and not unburned gasses igniting?

[PerryFamily]

I would think that it would be hard for creasote to form in any evaporator operating at peak efficiency.
A smoldering wood stove for sure.

[TerryEspo]

Could it be that the build up of creosote is from earlier, now that the pallats are burning proper and hot, it is igniting the build-up in the pipe.

Maybe a good chimney clean and burn away.

A pipe with no creosote will never have a chimney fire.

Hope that helps.

Terry

[PerryW]

Could it be that the build up of creosote is from earlier, now that the pallats are burning proper and hot, it is igniting the build-up in the pipe.

Maybe a good chimney clean and burn away.

A pipe with no creosote will never have a chimney fire.

Hope that helps.

Terry
my thoughts exactly. never heard of creosote buildup in an evaporator stack? Never heard of anyone cleaning a stack either.

Are it getting too much air? I would close the damper up all the way and make there there are not big gaps where addtional air is getting it.

Or, are you pushing a bunch of long wood into the firebox past the grates?

[MapleMounder]

If your pipe is glowing red and running in the 2-3000 range that is beyond unsafe but you know that that’s why you are concerned. At those temps there isn’t any creosote left. Creosote is created by flue gases that cool and solidify due to insufficient heat before they can exit the flue, again at those temps that can’t be the issue. I would lean more towards the woods that you are using is more a “flash fuel” and you have too much air, you are getting a rapid high temp burn in the fire box and the smoke (incomplete combustion) is igniting in the flue where it still has plenty of heat and is getting additional oxygen, possibly through the seams in the pipe at the joints. Might be too much air in the firebox, I agree, shut down the air intake and/or damper to reduce draft.

[Super Sapper]

I burn pallet wood also, I would suggest not filling the firebox so full. You may have to fire more often but I think it will run better if you do not stuff it full.

[Asthepotthickens]

I would say more draft, I burn pallets and hardwood, when we boil at night we see flames comming out of the chimney not a chimney fire the pipes are as clean on the inside as they are on the outside. Never burn wood with paint on it, wet wood or plywood.

[maple flats]

I also had flames out the top before adding AOF. It was not a chimney fire, but rather unburned gasses getting fresh air and re igniting. I also have never heard of creosote in an evaporator. The temperature if correct or even close is truly a danger however. I also suggest, add less but more often. Pallets burn real hot, so you may only need a small portion of what you used to need with your previous wood. Start by using maybe 20% of what you were, then increase the amount with each fueling until you find what you need. The 20% might even be right.

[Big_Eddy]

You're overfiring. When wood is heated - it breaks down into combustible gases which burn when combined with oxygen from the air. With your slabs and pallets, those gases are being produced in greater quantity than you have air to combine with, so they are being drawn up the chimney by the draft. As soon as they hit the top of the stack there is plenty of oxygen and they ignite giving you the 2-3' flame out the top of the stack.

Shutting down the air reduces the heat in the arch, reducing the rate at which the combustible gases are being generated. It also restricts the draft so the gases are not sucked up the stack as fast.

Fire less wood more often. I listen to the arch. As the roar decreases - I add more wood.

[802maple]

Flats is correct, there isn't any fire in the stack, it is hot but there is no oxygen for it to burn until it is reintroduced to the outside air, and then it becomes a torch. This is why AOF arches burn so efficiently as they burn all those gases before they get out of the stack.
I also had flames out the top before adding AOF. It was not a chimney fire, but rather unburned gasses getting fresh air and re igniting. I also have never heard of creosote in an evaporator. The temperature if correct or even close is truly a danger however. I also suggest, add less but more often. Pallets burn real hot, so you may only need a small portion of what you used to need with your previous wood. Start by using maybe 20% of what you were, then increase the amount with each fueling until you find what you need. The 20% might even be right.

[PerryW]

My 20' stack used to look like a torch. I think switching from 24-30" wood down to 18" and keeping the wood close to the front has helped it. Or maybe the big 3/4" cracks that have developed on evaporator both doors are letting in air-over-fire??

[Scribner's Mountain Maple]

Alright, good information thanks for all the ideas. After reading through the posts, I think I am getting both too much air and putting in too much wood. I boiled again last night and had the same problems. I didn't let it get as far/hot as it had been. Meaning as soon as I heard the jet engine fire up (chimney fire sounds just like it) I shut the damper door. But I do have large gaps in my front doors and a gap at the back of the arch where there is another door below the stack. I've plugged where I can with insulation.

The fire is tearing through my back pans and is flame all the way from the front of the arch to 2-3 feet above stack. Like I said before the GPH rate increases almost instantly but man it is scary. I wish I had a video to post of the minute of time that passes when the stack ignites and it starts to glow. Then the glow works its way down the stack until it reaches almost to the bottom. That's when I start to freak out and shut it down. It is something to see it happen that is for sure. Few more boils left and I can re-tune the arch for next year.

I will try using a little less wood, firing more frequently and reducing the amount of air I let in the damper. I have also been pushing wood past grates and will try to keep it all closer to the doors. Thanks.
Ben

[802maple]

What is heating your stack is super hot gases and not the flame, but I would advise that you cut back on the wood and fire more often as you said you are going to do.