The Stove 'Backfires'...Is This OK???

Dan McCartney
Posts: 28
Joined: Thu. Dec. 21, 2006 9:03 am
Stove/Furnace Make: Lopi stove and old ARCO Boiler
Location: Northwest Ohio

Post Wed. Dec. 27, 2006 12:10 pm

Whenever I start my cold stove I get a big "Boom"! Let me explain and see if you can comment. I start my stove with wood; bunched up newspapers with kindling, then small logs, then the bituminous coal. After the kindling and small logs have been burning about three to five minutes, I get this BOOM that sounds like you hit the side of the stove with your fist. I have a shroud (if that's what you call it) around my stove for the air to circulate from the blower. The sound is like a drum; hollow, as if the shroud was thumped. I see no action in the firebox, no sparks or wind inside, nor any bursts come out the chimney. It appears to be in the "shroud" area. It causes no damage, no mess, and can't be detected anywhere except for the sound. I have studied it closely, observed intently, and still can't see any effects with my eyes - only the audible sound of the boom. All I can imagine is some trapped air, expansion, cooling-heating, something compressed or trapped? We are all use to it and my wife uses it as her wake-up call; when the stove booms she knows she can get out of bed and find a roaring fire! Can you tell me why this is happening and what I can do to see if it can be prevented? PS - if it makes any difference, my stove pipe exits horizontally from the back (?) Dan.

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Hand Fed Coal Stove: Franco Belge model 10.1475
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Post Wed. Dec. 27, 2006 1:25 pm

Hi Dan:

I'm guessing that the shroud is made of sheet metal rather than cast iron or plate steel. If so, the boom you hear might be from the sheet metal expanding as it begins to heat up. This will sometimes happen in a forced hot air system as well; as the ducts heat up and deform a bit, it will make a booming sound.


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Post Wed. Dec. 27, 2006 2:03 pm

My Mark III will do the same thing if I load it too full all at once and it
isn't really roaring.
I have a feeling that it is worse now that I "sealed off" my window
for secondary air supply. (ahah, maybe that's why it's there)
anyway... without that air supply coming in around the glass like
it did when I first changed the glass (and used the gasket on just the
sides as instructed), I am noticing more tendency to backfire if I'm
not careful when I load. Last nite, I was teasing it, it was loaded..
ash door open, sort of smoldering, I'd close the ash door and open
the coal door, just a little, and close it.. then small "whoosh", ignition,
but with the door closed, it'd go back out out. I did it a few times, (yea,, it was the pyro in me coming out). But, I really think that if I was to
pull that extra gasket material out from top and bottom of my window that I would see ignition quicker. I just hate the thought of how the stove
burned when it was like that last month. (very hard to regulate, and
I had a few of these last winter, and was nervous at first, but after a while I learned that I could minimize it if I spent the time. Usually, it
happens with a rush load, without the stove really going.

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Hand Fed Coal Stove: Harman Mark III
Coal Size/Type: Stove, Nut / Anthracite
Location: Farmington, New Hampshire

Post Wed. Dec. 27, 2006 2:35 pm

Dutch, if you are having to block the openings in the glass then you have issues elsewhere. I have a Harman Mark III myself, and I blocked that opening myself thinking it would help my draft problem. What I found was I had too much draft, whick I think is the problem you have. By adjusting the Baro damper the problem went away. Harman put that design there for a reason, that is why I searched further to find my problem.

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Stove/Furnace Make: Brunco
Stove/Furnace Model: Hearthglow
Location: NE Ohio

Post Thu. Jan. 11, 2007 10:41 am

I have a question regarding the boom everyone describes:

Does the chance of a boom increase if the hand damper above the flue is closed almost all the way after reloading with fresh coal? I would think "yes" based on the discussion of gases escaping into the chimney from the stove coupled with the fact that the rate of the amount of gases escaping would be less with the hand damper closed.

So should I keep the hand damper open all the way (letting that heat go up the chimney) until the whold bed catches after reload, or should I continue closing the damper right after I add a fresh load of coal, with the ash door open.


Dan McCartney
Posts: 28
Joined: Thu. Dec. 21, 2006 9:03 am
Stove/Furnace Make: Lopi stove and old ARCO Boiler
Location: Northwest Ohio

Post Thu. Jan. 11, 2007 2:25 pm

My "boom" (chic-a-boom, boom, boom!) I'm convinced, has to do with my sheet metal shroud, and does not have anything to do with my combustion or gasses. This shroud around my stove, for the air circulation, must be expanding or moving somehow when going from a cold stove to a hot one so quickly. My boom sound is not inside my firebox, and sounds exactly the same as if you hit the side of my stove with the flat of your fist. Actually, we are all kind of use to it and nobody jumps anymore! Very livable. Dan.

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Post Thu. Jan. 11, 2007 2:47 pm

Italia, you will increase the time it takes to get the fresh coal burning if you let secondary air go up the chimney. This reduces the under fire draft.

I'd leave a 3-4" open spot of hot coals when you load on fresh coal. Once the fresh coal is all burning well, then you can either add a shovel full to cover the original 'hot spot' or rake the new coal over the hot spot to level the bed. This is the method I use. Usually just a poke or push wth the shovel or a hoe will expose a hot spot to be my pilot light.

The 'hot spot' acts like a pilot flame to ignite the fresh coal gas at a gradual rate instead of getting a small explosion.

Hope this helps. Greg L


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