Help! Flames out the chimney pipe!

[ScottyWelden]

Boiling last night in my not-quite legal shed and shooting a bunsen-burner type flame into the sky. I was glad my neighbors would not call the fire department. I have read about air-over fire, but I really don't want to get that high tech. I have a 4-foot cinder block/fire brick evaporator and a 7-8 foot vertical pipe (6"). I have air coming in under grates (about equal in volume to the 6" round). I burn pine, If I add a lot of wood, I get the chimney flames for 10-15 minutes. If I don't add enough wood, my boil gets pretty wimpy. I've tried reducing air intake, increasing air intake, leaving the top of the door slightly ajar --but no solution so far. Any thoughts for me?

[psparr]

The main culprit is lack of air. The gasses are starved for oxygen, and once out of the stack have enough air to ignite again.

[82cabby]

I had the same issue with my evaporator and two things fixed it:

I added ceramic blanket between the fire brick and the wall of the evaporator
so more heat stayed in and I didn't have to run the blower so hard to get a boil.

I added "baffles" in the flat portion under the pan after the firebox but before the flue.
That way the flue gases have to go through a longer route and they have some
Turbulence before they exit. More time to dump heat.

[ScottyWelden]

Any ideas for an easy fix?

[82cabby]

Can you post a picture of the evaporator?

[ScottyWelden]

1555315554

[82cabby]

It looks like the ramp at the back your firebox go straight up to the flu. Anything you can do lengthen that path and add turbulence will help. You want the fluegases to dump as much heat as possible before going up the stack.

[Biz]

I get flames frequently from the top of the stack on my 18x48" CDL also. No blower, draft open to first notch, about 12' of stack. Can't reduce stack length without adding a couple of elbows. Added some small restrictions this season which helped a little, otherwise it is bricked as designed. The firebox is on the small side so options are limited. A poor design maybe? It does boil well when flames are shooting out.

Dave

[Sunday Rock Maple]

How about a bag of marshmallows, a Hershey bar, some Graham crackers and a sharp stick?

[82cabby]

Here is what I did with mine. The metal plates at the back extend about 4/5ths of the way across and the fire bricks bring the gap down to about 2.5 inches. The flue gasses have to go back and fourth and tumble around. I get the most vigorous boil right over that section.

15563

Sorry it is sideways, it is right side up on the phone and on my computer....

[ScottyWelden]

excellent info, guys--thanks so much!

[maple flats]

You need more air and especially more turbulence. A tough issue with a block arch. See if you can locate an old oil burner and if you can, try running the blower on it aimed into the middle of the fireball under the pans. Since it requires high pressure air a squirrel cage blower will not help, they are high volume but low pressure.
Your cfire is just using up the oxygen and when the remaining hot gases get to a fresh supply of oxygen they re-ignite. That is what AOF fixes, but it is a tough one to fix on a block arch.

[Sugarmaker]

Keep boiling! You dont have to worry about creosote! just keep a eye on the stack. they can get super heated and glow red then its time to back off the fire a little.
Regards,
Chris

[Joe Hillmann]

The last two years anytime I had a good boil going I had flames coming out of the top of the chimney. We just kept an eye on it and eventually the tree branches nearby burned away far enough that they were no longer a concern. This year we have the same set up and the flames never come out the top of the chimney. I don't know what made the difference but I'm not to worried about it.

[maple flats]

The last two years anytime I had a good boil going I had flames coming out of the top of the chimney. We just kept an eye on it and eventually the tree branches nearby burned away far enough that they were no longer a concern. This year we have the same set up and the flames never come out the top of the chimney. I don't know what made the difference but I'm not to worried about it.
The likely cause was the lack of tree branches above, why run a flame there if there's nothing to burn?

[Joe Hillmann]

The likely cause was the lack of tree branches above, why run a flame there if there's nothing to burn?

I don't think that is the case. The fire was coming out of the chimney like a torch and the tree branches just happen to be in the way and got burned. I think the difference is possibly the bricks in the arch are in a slightly different configuration than they were before and the fire gets more air at the back and that allows the gasses to burn inside of the arch instead of burning when they get enough air once they get out of the chimney.

[mellondome]

Adding smaller amounts of wood on a more frequent timing will also help. When you add a lot of wood to the fire, it will gasify and if there is no oxygen for it to combust with, it will do so at the top of your pipe where it hits the air.

[sappytapper]

eventually the tree branches nearby burned away far enough that they were no longer a concern.

this made me laugh harder than i'd like to admit