OWB explosion

[NSMaple1]

Maybe you need to extend your stack? To increase your draft?

Could have been an odd sporadic localized thing going on (swirling winds from the wrong way or something, plus a warm odd air pressure day?) that caused it to actually draft backwards, or create positive pressure down the chimney, that held the smoke in? Then went kaboom with the gush of fresh air from the fan. The little hole you mentioned combined with adequate draft is likely designed to stop something like this from happening. (That little hole isn't blocked somehow by chance?)

Still a bit boggled by the blowing water...

 

[farmer steve]

i think the OP needs to contact the MFGR about this problem. I don't have a OWB but with all the repilies about this i thin there is a serious mfging defect.

 

[cantoo]

I've had an owb for years. An explosion in the firebox that causes water to shoot out the top of the unit is pretty much the end of the unit. They would not take that much expansion, it would crack welds.
If it has happened twice I would suspect that it's a boil over event. I have had mine over fire before and boil out water until the level was lower than some of my heating tubes. Then the owb fired again and it cause rapid boiling, hissing and water shooting out the fill hole. Basically like a stove burner on High with a pot of water sitting on it and only an inch of water in the pot. Violent boiling and steam because there is so much heat and not enough water. There are sensors that you can mount that will shut off the fan if the temp gets too high. If the draft door is stuck open it would still natural draft though. I've also had my owb firing good, gets water up the temp and then damper door shuts down, then the OWB went into steam engine mode, huffing and puffing smoke out everywhere. OWB's can be a handful.

 

[crowbuster]

Can you clean the chambers going from the firebox to the chimney ? Seems like there may be some sort of backup somewhere, though I have not seen or heard of this.

 

[bowtechmadman]

Nope wasn't the O - E site...it was the 6 letter word site that starts with H and ends with TH, with an EAR in the middle. Definitely, contact the manufacturer.

 

[NSMaple1]

I'm not sure how much it matters, but this seems to be a coal boiler.

Not saying it won't burn wood OK - but that's not what it was designed for.

 

[redytorace]

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.

My temp is set at 165 with 15 degree differential. So fan kicks on at 150 degrees and shuts off at 165. I hope to find a solution too!!

 

[redytorace]

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.

Draft door and soleniod are both moving freely. I keep them sprayed down with a dry graphite lubricant. I may try the shim one day this weekend when i'm around all day.

 

[redytorace]

I'm not sure how much it matters, but this seems to be a coal boiler.

Not saying it won't burn wood OK - but that's not what it was designed for.

Yes it is listed as a "coal boiler" but their MF series (which is wood and coal) is exactly the same as the C series. I believe they just rebranded the MF as a Coal burner to get around EPA regulations. I do burn coal in mine when it gets cold. But right now with the mild temps. it's hard to keep a coal fire alive.

 

[redytorace]

Maybe you need to extend your stack? To increase your draft?

Could have been an odd sporadic localized thing going on (swirling winds from the wrong way or something, plus a warm odd air pressure day?) that caused it to actually draft backwards, or create positive pressure down the chimney, that held the smoke in? Then went kaboom with the gush of fresh air from the fan. The little hole you mentioned combined with adequate draft is likely designed to stop something like this from happening. (That little hole isn't blocked somehow by chance?)

Still a bit boggled by the blowing water...

Heatmaster recommends keeping your stack as short at possible. There's about 18" of stack that comes out of the top of the stove, I put a metal carport over the stove, so I added a 3' extension to get through the roof of the car port. Right now the stack is about 16" above the peak of the carport. I've never experienced a backdraft to the point where no smoke was coming out of the stack....there's always a little bit of smoke coming out of the stack even when the stove is idle. That little hole is not blocked. The entire structure of the stove is stainless steel (firebox and waterjacket) so the firebox is much thinner than a mild steel furnace. Being that it's a little thinner than a mild steel firebox, that may allow for a little expansion and energy transfer into the water jacket when the explosion occurs.

 

[redytorace]

i think the OP needs to contact the MFGR about this problem. I don't have a OWB but with all the repilies about this i thin there is a serious mfging defect.

The seller/installer has been very helpful in trying to resolve this issue. He heats his home with the exact same stove right now, so he understands the ins and outs of it. He is going to call the manufacturer today.

 

[redytorace]

I've had an owb for years. An explosion in the firebox that causes water to shoot out the top of the unit is pretty much the end of the unit. They would not take that much expansion, it would crack welds.
If it has happened twice I would suspect that it's a boil over event. I have had mine over fire before and boil out water until the level was lower than some of my heating tubes. Then the owb fired again and it cause rapid boiling, hissing and water shooting out the fill hole. Basically like a stove burner on High with a pot of water sitting on it and only an inch of water in the pot. Violent boiling and steam because there is so much heat and not enough water. There are sensors that you can mount that will shut off the fan if the temp gets too high. If the draft door is stuck open it would still natural draft though. I've also had my owb firing good, gets water up the temp and then damper door shuts down, then the OWB went into steam engine mode, huffing and puffing smoke out everywhere. OWB's can be a handful.

The firebox and water jacket is Titanium Stainless Steel on the Heatmaster, so is much thinner than the mild steel fireboxes used on other stoves. It's a large firebox and oval shaped, so I guess I can see where some expansion can occur without breaking the welds. There's only 2 oval shaped welds on each end of the firebox. It definitely was not a overboil...the explosion occurs in the firebox. It blows soot/ash out the chimeny and back through the draft door. Thanks for your thoughts.

 

[redytorace]

Can you clean the chambers going from the firebox to the chimney ? Seems like there may be some sort of backup somewhere, though I have not seen or heard of this.

Yes there is an access door that you can open, take out the baffle, and clean the entire chamber. I spent about 5 hours cleaning and scraping the stove the week before I fired it up. It was close to new condition when i got done cleaning it, so there was no blockage or backup.

 

[panolo]

It's not evacuating the gas and smoke quickly enough out the stack and when you get oxygen added to it and a flame sparks you have enough in there to create the explosion. That's what I believe. Flue obstruction, poor draft, fan issue. Heck it could be an issue with the way they welded the passes inside the stove.

 

[woodfarmer]

That panalo, is exactly what will happen. Nothing more than a build up of gases that ignites. If there is a fire burning, the fan has to be on.

 

[NSMaple1]

Yes it is listed as a "coal boiler" but their MF series (which is wood and coal) is exactly the same as the C series. I believe they just rebranded the MF as a Coal burner to get around EPA regulations. I do burn coal in mine when it gets cold. But right now with the mild temps. it's hard to keep a coal fire alive.

Are you sure they are exactly the same? Maybe wood is more prone to something like this when it is shut down, than coal is? Therefore their wood units might have small differences to avoid it? Like say a bigger hole? Or something else?

Also I would be pretty leery about the strength of the firebox after many of these episodes. IMO it would take a lot of firebox flex to blow water out the top - it's not likely designed to take any of that. So each one would be working on a weak spot somewhere, making it weaker. Bending till it breaks kind of thing.

 

[Stihl310]

I’ve only seen mine do something even remotely close to this about 3-4 times. This would happen when I would put kindling or cardboard in to get a fire started.

Basically what would happen is the fire would begin to consume oxygen faster than the fan could supply it, thus snuffing the fire for 10-15 seconds. In that time gases were building up and eventually it would relight with a loud “POOF”.

That being said it is nothing nearly as volatile as what the OP is stating they are witnessing.

I’m only throwing this out though because I think it may just be a little bit more powerful example of what I’m witnessed a handful of times.


Sent from my iPhone using Tapatalk

 

[cantoo]

Stihl310, that about what mine does too and it sounds like a freight train huffing and puffing until it fires. And it's usually cardboard or papers that cause it. Doesn't do anything to the water though.

 

[lefturnfreek]

What are you burning? Just wood or wood annnd ...?

 

[redytorace]

What are you burning? Just wood or wood annnd ...?

Just wood right now. It's been spit and stacked for about 8 months. Once it gets cold I will burn wood and coal.