Minor Explosion In Coal Stove

I find that with my 50-93--the thermo flap takes any of my lil or big booms --Oh hush Rick--below the flap door I can usually see an ash dusting, nothin major, but it's there. Of course that's with following SOP for the tending process on the 50-93

I'm having an issue with "puff backs" lately. but I'm not getting them while loading. its happening an hour or two after loading. and they are big, had one last night that blew the bottom part of the barro door off ( the part you flip around depending on if its a vertical or horizontal install). that one and the one i had the day before shook the floor of the house. but the the first of the two sent flames up the flue past the barro for about 30 seconds. To try to correct this issue last night and today i ran the stove with the over fire draft knob (i think thats what its called) cracked open just a touch. When i got home today the barro was intact so i guess i did not have a large puff back today.

My stove is a natural draft boiler, when it go's into "high fire" an actuator opens a small flap on the ash door and when it reaches its preset temp the flap closes. I think that my stove is going into high fire, building temperature, the flap closes and the fire dies down, the 2 hour old coal releases more gas, and eventually enough heat and oxygen build up with the gas and.... boom....

my thought is that by leaving the over fire damper knob open just slightly it will keep enough oxygen in the firebox that it will continually burn the gas off rather than all at once.

Am i on the right track? is leaving the over fire open some going to hurt anything? will it cause me to burn more coal? any input would be a great help.

I think you have it figured out. I would leave more than a crack in that over fire air. I don't think you will see a noticeable difference in the coal burned.

franco b wrote:I think you have it figured out. I would leave more than a crack in that over fire air. I don't think you will see a noticeable difference in the coal burned.

just to make sure we are talking about the same thing. i was planing to leave it open pretty much indefinitely. is this what you had in mind?

Yes. Some over fire air all the time. It is not just to burn the gasses from fresh coal but to burn the carbon monoxide that builds up in an established fire when starved for air. Ideally some sort of fixture similar to the antique stoves intended for bit coal that feed heated air just above the fire pot would be best.

I also leave just a smidge of over the fire air. I used to run mine sealed tight from any over fire air but was having puffing issues. This is copied from another post I made and my opinion based on my own observations - some may disagree

Come on Fred, who doesn't like some hot lil blue dancin ladies I'll throw in my opinion on the whole thing, cuz I've wondered the same. Bear with me, there is a lot going on here... It seems to me that if the coal bed is under a particular temperature, there are no flames and any over the fire air will result in wasted heat going up the chimney, although you may need this heat to help support your draft. BUT, if it gets above a particular temperature, there is enough combustible gases coming off the top of the coal bed to support flames when air coming in over the fire is introduced (like you've noticed). There are a couple things that can happen at this point.

#1 - These gases, without any over the fire air will simply float up and out the chimney. (wasted potential heat)
#2 - These gases, without any over the fire air could build up in the fire box and flash. (puff back)
#3 - These gases, WITH just the right amount of over the fire air, will yield me a few more BTU's

Number Three is tricky.. Meaning too much over the fire air will net you lost heat going up the chimney (in the form of heated air) and at the same time, not enough over the fire air will also net you lost heat going up the chimney (in the form of unburnt combustible gases). SO in my opinion, the perfect case scenario is the right combination of under the fire air (primary) and over the fire air (secondary) and that these air feeds are completely independent of each other. Meaning, primary air can't bypass the coal bed and act like secondary air, which was a huge problem for me. This combination will change based on just how hot you are pushing the fire. This is based on my own thought and observation. I would love to hear some others' thoughts on this also! Results and opinions may vary, some side effects could be life threatening (probably not) or are just a lot of fun to watch (Fred)

Thanks for your input Lightning and Franco b.

i burned last night and today with the over fire air open some. I had foil over the baro because it was going to be warmer here today (~50F) and my draft is POOR at those temps. when i got home the foil was pushed back away from the baro, so i guess i did have a puff back today. it must not have been too bad because the foil was not pushed back very far. after i discovered this, i opened the over fire air up a little more. it is currently at 3/4 turn open.