Last night I walked into the living room and heard BOOM! Big puff of smoke came out of the stove, and I had a "WTF" moment. I thought... did someone just put an M-80 in the woodstove? About 30 seconds later, BOOM! Same thing. My next thought was that there was something wrong with the air in the stove, so I grabbed my gloves, walked backwards over to the stove, opened up the damper, and it instantly ignited into a raging inferno. I let it burn down and it resumed normal operation. Did some research, and this is what I think happened: We had a pretty hot coal bed. My wife loaded a bunch of woodworking scraps in. (Read, small tinder-like and extremely dry wood) She waited a minute for it to ignite, then closed the damper and walked away. The fire produced a ton of combustible gases but did not have enough oxygen to burn. It "inhaled" some air through the chimney. All the gases lit at once. Processes repeated until I gave it more air. Lessons learned, don't load small wood into an established fire and close the damper! I did an inspection of the woodstove this morning. Thankfully no damage, just scared the crap out of us. (For reference, it's an enviro Kodiak insert EPA style (non cat stove))
Yeah the science makes sense, never thought that it would happen in practice, and I've never managed the stove to be "backdraft careful" although that'll change. Now my wife's all scared about loading the stove. Funny, my first google search was "Does Black Walnut explode in a woodstove" because that's what I loaded in, black walnut scraps and I've never burned it before.
Your thoughts are exactly right: the wood was outgassing rapidly, making a LOT of fuel (flammable smoke) but did not have enough oxygen to actually light. After some time goes by, enough oxygen does make it into the stove via the normal draft (not coming in from the chimney almost certainly) and poof- the entire fuel load lights all at once. Then starved for O again and the process repeats. Lumber scraps are really tough to burn if you put a lot of them in the stove at once, say, more than 1/4 full or so. Lumber scraps mixed in with regular cord wood splits are usually OK, again as long as the majority of the fuel is cordwood. But a stove with a lot of lumber is impossible to control because it outgasses so quickly that you either make a creosote mess and usually have back- puffing, or run the stove with enough draft to keep flame in the stove and it usually overheats badly. And as bad as kiln dried pine lumber is, something like cedar shingles are even worse. Brian
I had a Tempwood with a 12" diameter disk for a loading 'door' on top. And I had a dog. And I had an endless supply of <mostly> hardwood pallets I was burning. The stove was in the living room, which is on the long side at 24 feet, and opposite the wood stove was the front door with a full size couch on either side of that door. Of course the mormal walking path, for man or beast, was between the wood stove and the couches. But now and again, the stove would back- puff, causing a loud clang when the disk 'door' crashed back down into the stove, and of course the stove belched smoke and occasionally fire when it did back- puff. Needless to say, the dog was quite impressed by all of this and after one of those happened, instead of walking between the stove and the couches, he would walk along the edge of the couch, actually touching it to keep as far away from the woodstove as possible, then make a left turn hugging the end of the couch, into the well between the couches, rub against the door, the other couch and slink along the second couch..... all the while hard- eyeballin' the stove. But then things would calm down for a week or so and he would slowly calm down about the stove and just walk by it normally again..... and that is about when it would back- puff again, starting the whole terror cycle over again. Hysterical to watch. I do not have the dog or the stove anymore. Pepper was a fantastic 'member of the family' and I still miss him around 20 years after he left us..... but I do not miss that Tempwood in any way, shape or form. Or, for that matter, burning pallets after taking them apart (OK, crushing them) with the teeth on my backhoe. :-( Brian
Yep, you got the gist of it. If you are gonna load kiln dried lumber scraps (or a lot of real small stuff) you have to limit the amount...especially if you are loading on hot coals...or you again will have the scenario that you experienced last night. If she had let it burn with the primary air open for a little longer and then closed it in small increments over a 5-10 minute period, it would probably been OK...may have overfired though...as others have said, the best practice is to load mainly cord wood in when you are gonna burn that kind of stuff.
Had more than a few of those occasions brought on by my own doing. I find for me and my stove (in a nutshell) if I kick a load hard off the start (let everything get charred, lots of flames, burning crazy) I'm most likely turning the air down in careful steps other wise you have too much hot wood/smoke/wood gas, and a quick turn down of air will stall the fire, and give me the woofs. Sometimes pretty dramatic and sometimes the stove goes dark, and then pretty bursts of fire in mid air. I have better luck letting some of the wood char/some fire/not burning crazy, and start shutting down the air, and I seldom have a woof! Basically if there's fire hitting the baffles, she'll lug herself along and not stall. There's just not enough wood gas or temp to light up a firebox full of smoke. Of course there isn't a fire box worth of smoke to burn up anyways. But... it takes the fire longer to get up to max temp. Just remember, this is my stove, my situation, and probably not normal burning practice. What works for me may not work for you. Run your stove how it works best.
I've had this happen too. Does scare the crap outta ya. On reloads I make sure the damper is wide open, and leave the door cracked as well until the load is rippin'. Small steps about 3-5 minutes apart when closing the damper and I haven't had it happen again.
