The stove 'backfires'....Is this OK???

[Gary in Pennsylvania]

I betcha THAT subject line got your attention! But it’s true.
And it happened again this morning….And I can almost predict when it’ll occur.

Lemme tell you the circumstances and you tell me if I’m prolly right or wrong….and if that’s ok.

So…..It’s been pretty warm the past couple of days. I’ve been using less than normal amounts of coal. I was off work yesterday and didn’t need to put a big bucket on to carry me through the day……so I added through the day – just enough to maintain.
Last night just prior to settling to bed, I tossed a half bucket in, set the draft, and went to bed.
This morning the house was warm ( Man….it’s gotta be in the upper seventies! ). I went down to check the fire and it had burned itself low. After giving a good shake, I had only two inches base left…..and that base wasn’t humming….It was a little on the weak side. So I went outside to get a full bucket ( I’ve still yet to post pics of my coal bin ) because I was going to work today ( I’m there now ). This bucket had to last until nearly 5:00pm ( and it was 6:00am at the time ), and the only thing my wife knows about the stove is where it is and don’t turn the fan off ( she’s NO help with it! ). I wanted to make sure that the bucket I add catches well so it can sustain the day – especially since the warm predicted temps mean that I will draft the stove low today.
Soooooo……I open the coal door, toss in the bucket of coal, CLOSE the coal door, OPEN the ash door and begin to shovel out the ash.
Now I have a fresh bucket of coal (on a not-so-strong bed ) with the coal door closed with the ash door open is key to my backfire. What is happening is a mound of cool coal is on top of a bed gulping fresh oxygen through the ash door. I have the door open for maybe two-three minutes. That’s long enough for the bed to get red hot…the bottom of the mound to get safely lit……BUT THE TOP of the mound isn’t screaming hot yet, but IS warm/hot enough to be giving of its flammable gas (or whatever ) but not catching. With the strong flow of air up through the bed/mound, those flammable gasses escape quickly out o the stove and up the chimney ( I have a coal stove fireplace insert ). But when I’m done scooping the ashes and close the door, the evacuation of gasses ceases immediately. They collect quickly in the void above the bed and, in a short matter of time, ignite in the increasing temp inside the stove. I get a muffled whhhhhooomp! And dust is forced outside from the seal of both the coal door and ash door and my wife complains that the stove makes the downstairs smell like warm fart. After this ignition…..my mound has the characteristic dancing blue flame above it ( But NOT before the ignition ).

Now…….If I do the SAME STEPS as above but have a rip-roaring hot bed instead of a wek one….I get no backfire…..I think that’s because the really cookin’ bed bring my mound to up to temp fast enough and I get my dancing blue flame immediately.

Is my assumption correct? Should I worry? What do I do to prevent this?

Thanks for any input!!!

[LsFarm]

Yes you will get ignition of flamable gases when you dump a load of fresh coal on a low fire. Even on a hot fire if the quantity of new coal is great enough.

It really isn't doing any harm as long as you have at least three screws in each chimney flue joint. Otherwise the 'whummp' you described can push the joints apart and ash gets everywhere. You can also get this sudden ignition if you open the door within about 30-45 minutes of adding fresh coal. You can lose your eyebrows this way.

To prevent or reduce the sudden ignition of gas, leave a corner or end of the hot coal bed exposed. With the added air from the ash door being open, this 'hot corner' will flame up pretty hot, and act like a good 'pilot light' going in the firebox, igniting any gas as it is created.

Right now, with the hot fire trying to burn it's way up through the new coal, the gas is just waiting for an ignition source. There is no igntion source till the fire finally makes its way up through the fresh coal, then whoomp!! If you provide a steady ignition source, the gas will burn off steadily instead of suddenly.

I have some old brochures about adding coal to a stove, and most recommend leaving some hot fire exposed.

Once the coal is all burning, then rake it level , filling in the low corner, or you will burn all the coal in the corner and have air bypassing the coal bed.

Hope this makes sense. Greg L

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[Pap]

Some thing like that happened to me last year, only worse! I bought my first coal stove last year, it is a Harman Mark III. I had it working really good thanks to the help from guys on this board. One Saturdey morning I shook the stove down, took out the ashes and filled the stove to the top of the fire bricks. I left the ash/draft door open so the fire would get going again. After about five minuts there was a loud WWWWOOOOSSSSSHHHHH ash dust flew out the ash door and it sounded like the stove was blowing up. The guys on here said it was the gasses lighting up!!! Needless to say I NEVER let the door open anymore.

Pap

[greg white]

Man it is funny hearing that happened to you,it WAS NOT when it happened to me,I thought my building was going to be a gonner.
It happens just like described above,when then gases or whatever from new load have not lit yet.They usta make cartoons about that back puff, it happens still just not as often.thanks for sharing.

[jimbo970]

does this ever happen on a stoker?

[LsFarm]

A stoker should always have an area of open flame and red coals, so it should not be a problem.

The only way I can imagine getting a backfire would be if the stoker's feed mechanism pushed a lot of coal over the top of the line of burning coals. This could only happen if for some reason the ash was not falling off the end of the burner bed. Maybe from a clinker or an incredibly over-full ash pan. ???

Greg L

[Yanche]

It's never happened in my Alternate Heating Systems S130 stoker boiler. Of course the boiler design is much different vs a wood/coal stove.

Yanche

[SMITTY]

This happened to me alot when I first started using my Harman Mark I. I've had some good ones!

There is a large build-up of flammable coal gasses whenever fresh, cold coal is thrown on top of red-hot coal. Normally, it just goes up the chimney. But if I open the ash door or loading door (after loading) after having the door closed for a few seconds, it will ignite rather quickly! nfire:

Now, if I have to open any door after it's been closed for any length of time (with no blue flame), I just crack the top door & SLOWLY open to let the gasses flow up the chimney.

If you don't see flame, use caution.

[barley master]

sometimes this will happen and sometime it wont. i used to make mine flash on purpose years ago with the belge. it also happens on my not so air tight air tight wood stove in the hi effiencey mode. it's sometimes very
violent until all the gasses are released from the wood.

what is happening when this takes place is a combination of heat, air and fuel are mixed together at the proper levels for this to happen. the heat and air is already there. then you add the fuel. with the heat that is present it starts to distill the gasses out of the fuel when enough gas is present it does and will flash to varying degrees. if your using a low vol. coal (around 3%) the flash may not be noticed. what you will see is a slight blue flame for a short duration. the higher levels of accumilated gasses the bigger the flash will be. once all of the gases are distilled then what is actually being burned is the fixed carbon.

i dont know, because i have never burned soft coal but with the higher levels of vols this may occur more frequently?

[LsFarm]

When I was burning my really nasty Bituminous coal last year, I could blow the chimney pipe off the backof the boiler with the 'backfire'.

The first time it happened I had loaded a five gallon bucket of coal on a hot fire, closed the door and was walking back to the house I heard WHOOSH! And looked back to see a huge discharge of soot, smoke and ash come out the chimney, shooting 15-20 feet in the air.

I ran back to the outbuilding, and the room was full of black soot and ash, what a mess!! The elbow at the back of the boiler had blow off, I had only installed one screw to hold it in place thinking friction was enough to do the job, wrong!! All joints have three screws now.

But of course, I didn't have to worry about cleaning the flue pipes or chimney for awhile!! It was a pretty impressive 'backfire'.

Greg L

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[mjwood0]

Seems like a good thing your stove isn't in your house! That would make a mess in my dining room!

[LsFarm]

The black soot was so bad that I put on a raincoat and goggles and powerwashed the interior of the 'boiler-building' last summer. Turned the wood framing from black back to tan again.

Yes, if it had been in my house, I'd have had to buy new carpet and furniture in at least one room.

Greg L

[mjwood0]

Here's hoping I have no such problems when I get mine installed. I hear stokers don't do this so I'm crossing my fingers! Especially since i just put down all new flooring where the stove is going to go!

[Berlin]

one time i forgot to put the screws back in the cap of the T after a cleaining and yes, what a mess it made, went through 8 rolls of paper towels cleaning hard surfaces and had to vacuum the carpet by hand with the wand attatchment. some advice; if it ever happens to you where you forget to put screws in a pipe with bituminous and you get soot on your carpet, DON'T use the vacuum in the traditional way with the carpet brush, rather use the wand attatchment and vacuum every place by hand, sucking the soot up; when you're done, there will be no residue and it'll be like it never happend, if you use the brush, you'll smear the soot into the carpet and ruin it.

[mjwood0]

I wouldn't have thought about it but it makes sense. The beater brush in the vacuum would definitely grind it in worse.

We're in the process of installing snap laminate "hardwood" flooring in the room where the stove is going to get setup. Should make it easier to keep the dust under control.