OWB explosion

[redytorace]

Sorry for the long post, but I have a important question for the OWB owners and I appreciate any help. Last year I had a Heatmaster C375 installed. It has a solenoid that opens a draft door and a fan that kicks on when it calls for heat. Twice so far (once last spring and once this fall) there has been a violent explosion inside the firebox. So violent that I heard it from inside the house and it blows water out the top of the stove and soot/ashes out of the draft door and into the fan. Both times it has happened within 10 minutes of loading the stove and within 2 minutes of the fan kicking on. I'm assuming it is from smoke and gasses building up inside the firebox..and once the fan kicks on and gets the fire going, the flame ignites the smoke/gasses which causes the explosion.

The major issue is each time this happens, the explosion blows coals/ashes/soot into the draft door chamber and all that debris in there prevents the draft door from closing. Air freely enters the stove and it will burn out of control unless I free up the draft door. Luckily I was home both times this happened and I was able to get the draft door freed up and closed, but my concern is that if this happens when I am NOT home, the fire will burn out of control and overheat/boil the stove.

Both times this happened the outside temp was only in the high 30's/Low 40's so the stove sits idle for several hours at a time. Has this ever happened to anyone or does anyone have any suggestions to prevent it from happening?? Thanks in advance for your help.

 

[Del_]

It sounds like you need some type of 'minimum burn' setting where some air gets into the firebox all of the time and when higher amounts of heat are needed to have the forced draft kick in.

Also having a stove sit idle with a large load of fuel for several hours at a time is a sign of poor use of the heating appliance.

This type of operation is what the newer OWB's are being designed to eliminate as much as possible. The are trying to engineer poor operator practices.

 

[Marley5]

I'm trying to wrap this around my head.....never heard of that before.

For there to be a violent explosion within the burn chamber air must be introduced.
The first place I'd look is the damper door.
Make sure it is a tight seal all the way around.
I take mine off every year and clean and sometimes file it then use a dollar bill all around the door to confirm a seal....saves wood also.

Another thing to check is door gasket.
AND do you have the required amount of stove pipe to prevent back draft ?

Here's what your your chimney should look like when damper shuts.....very little/slow smoke. That said....I'm not familiar with gassification boilers just the smoker's.

 

[NSMaple1]

I'm not sure why an explosion in the firebox would make water blow out? That would have to mean that the firebox expanded? Quite a bit - if it does really 'blow' it out. Which would make me then wonder about it's structural integrity.

It sounds like you need to load smaller loads when the weather is milder. Load for the load. Yes that would mean you would need to load more often, but it's a give & take thing. And maybe change the timing of your loading. If you are loading when the boiler is up to temp and isn't calling to heat, then you are loading a bunch of fuel in & starting instant big smoldering as soon as you shut the door. If you load when the boiler is below setpoint, then the fire should slowly build as soon as you shut the door.

 

[farmer steve]

what does the seller/installer have to say about it?

 

[CentaurG2]

Never heard of this problem before. You can get a puff the magic dragon moment if you open the door too fast but an explosion? The only way I think you can get an explosion is to superheat the water but this seems very unlikely.


https://www.youtube.com/watch?v=1_OXM4mr_i0

 

[bowtechmadman]

I've burnt with my woodmaster for 14 yrs and never experienced anything like that. I have lost my eyebrows in a puff the magic dragon episode...learn about that one quickly enough.

 

[redytorace]

Thanks for the reply's guys. I'll try to answer most of your questions/concerns.

Del_ : I agree, it does seem the the stove is too air tight when not calling for heat so everything just smolders and gasses build up. Letting some air in all the time might keep the coals hot and the heat might push the smoke/gasses out the chimney instead of building up in the firebox, but i'm afraid that it would also over heat the water on days when it's warmer than usual (say 40 degrees outside). Also, the amount of wood i load in the stove is based off the outside temperature. I load twice a day no matter the temperature, so on warmer days I only put enough in to last 12 hours.

Marley5: This is not a gassification burner, just a smoker with a extra bypass before it goes out the chimney. The explosion happens when the fan kicks on and blows air into the firebox. My chimney is about the same height as yours, maybe just a foot or two shorter.

NSMaple1: It is a pretty violent explosion, so being that the entire firebox is surrounded by water, the energy transfers into the water jacket via minor firebox expansion I guess?? I do load smaller loads in milder weather. Like i said above, I load twice a day..so I only put in enough wood to last be 12 hours based on outside temps. I see what your saying about loading timing, but i'm sort of limited on that because I usually load in the morning before I leave for work and in the evening when I get home.

Farmer Steve: The seller/installer said he has never heard of this happening before. And they install a lot of stoves each year.

CentaurG2: Yes I'm pretty familiar with the fire ball you get when you open the door too fast. I've learned how to limit that from happening. The explosion comes from inside the firebox. My guess is it's from the smoke/gasses igniting once the fan kicks on and forces oxygen into the firebox and the hot coals or flame ignites the build up smoke/gasses.

Thanks for all the suggestions, I'm willing to try anything at this point haha.
Is there anyone on this board that has a Heatmaster C series stove or is familiar with the C series stoves have this same problem??

 

[redytorace]

There's a cutaway diagram of the stove. When the stove calls for heat...a solenoid opens the draft door and the fan kicks on. Air blows through the draft door and into the ash pan area before moving up through your grates into the coal bed.

When the stove is not calling for heat, the fan is off and the draft door is closed. There is no air going into the stove except for a 1/2" hole that is drilled in the middle of the draft door.

 

[artbaldoni]

I'm with Maple, two different chambers. Are you sure there is an explosion within the firebox, or just a dramatic "boil over"?

 

[redytorace]

The explosion is definitely within the firebox. It blows ashes and soot out the chimney and through the draft door and into the fan.

 

[spyder62]

Does this heater have a temperature/ pressure relief valve on it? Make sure nobody put a plug in it. It should have a pipe on it piped to within 6” of the floor. It definitely should have one on it.

 

[redytorace]

It is an open system (non pressurized).

 

[bowtechmadman]

Mine hasn't exploded and in temps above 20 I only load once a day...so I wouldn't think amount of wood is the issue. I also pack it extremely full when gone for a weekend. I load twice a day once temps start dropping below the 20 mark. I would guess a draft issue. When it's smoldering is there any smoke emitting from the chimney? Is all the smoke and gas not getting out and when the air hits it ignites causing the same issue as if you open the door too quickly but contained in the stove? I have dual inlets for draft front and rear and they blow right into fire box (I don't have grates). Any similarities in the weather on the day's it's "exploded," this could provide some clues. I'm guessing your just not drafting for whatever reason and it's igniting when air is introduced.
Might try ********** for more insight possibly find others with your same brand of stove.

 

[CentaurG2]

Pawing back through my memories, the only time I have ever seen/had something like this happen was with a shop stove. It had a good coal bed going and I dumped a real good jag of wet bark/saw dust/leaves rakings from a clean up on top of the coal bed. It took about 15 min and the stove went “poof” like spontaneous combustion or ignition of gasoline on a burn pile. I think what happened was the water from the wet wood boogers reacted with the hot coals to form producer gas (CO). Highly flammable and toxic. What were you burning in this thing when it went kablooie?? To shoot water out of the top from the jacket, it must have been a big kablooie.

 

[bowtechmadman]

Did I say a bad word? Just trying to share another forum that may provide valuable insight to solving the problem....

 

[redytorace]

Bowtechmadman: When it's just smoldering, there is a little bit of smoke coming out of the chimney. About as much smoke that is coming out of the chimney in Marley5's picture above. It does seem like smoke and gas is building up inside the firebox and igniting when air is forced into the firebox by the fan. Both times that it happened it was about 40 degrees out so the fan probably hasn't run for a while so there wasn't a real hot bed of coals in the stove when I added more wood to it. I opened the door and the coals and half burnt wood was just smoldering. I busted everything up and added more wood. 15 minutes later the fan kicked on and withing a minute I heard the explosion.

CentaurG2: Right now I'm just burning hardwood in it that I cut and split in the spring. It was a big boom.

My best guess is with the warmer temps. the stove wasn't calling for much heat throughout the night so therefore there wasn't a real hot bed of coals in there when I loaded the wood. Since there was no heat to push/draft the smoke out of the chimney efficiently, it built up inside the firebox. Once the stove called for heat and the fan kicked on, the air got the coal bed hot and ignited the build up smoke inside the firebox. That's the only thing that i can figure happened. So how do I prevent this from happening again? Somehow I got to get the smoke to escape the firebox more freely when there is not a hot fire burning. Or just don't burn when the temps are this warm.....??

 

[Marley5]

You should be able to burn anytime, any temp.
I know many who burn all summer heating water.
Curious to know your set temps.
Mine is 175/185.
Still blows my mind and really hope you find a solution.

 

[CentaurG2]

On our central boiler, during warmer weather, I have had the draft door get sealed shut from creosote buildup. It seals so tightly that the solenoid that opens the door will pop the fuse. Perhaps you have a similar problem that is causing the buildup of the explosive gasses. I solved the problem with a little high temp anti-cease. Perhaps a small shim (bent paperclip?) to keep the draft door open just a small crack, will solve yours?? I would try this when you are around to make sure it does not cause a run-away boiler.

 

[Deleted member 149229]

Did I say a bad word? Just trying to share another forum that may provide valuable insight to solving the problem....

Did you mention the other site that starts with O then has a P and last word is E?