vent fire in a pellet stove

[Snowy Rivers]

OOOOOOOK
Our Whitfield Prodigy 2 that has a 24" direct vent system had a vent fire this morning.

I usually run the stove on low all the time and this morning decided to bump the thing up on number 2 to warm the house a little faster.

I went in to the computer room /office to have my coffee and surf the net a while, and came out for a second cup and noticed that the stove sounded different.

I went to investigate and then noticed a smell that was unusual, suspecting a motor going away I investigated further.

There was smoke coming off of the Pipes inner surface which was extremely hot and nomally is barely warm to the touch.

I ran outside and the vent elbo was smoking hot.

Shut the fuel off during the first inspection.

I got heavy gloves and then removed the elbo and inspected the pipe, YEAH BUDDY the normal little fuzzy sooty coating had lit off and waas glowing red hot.

I removed the inner wall thimble and inspected the insulation and the wall board and things were very warm but no issues.

I had ASSUMED that the nut shells did not produce creosote, but they do leave a slightly oily residue when burning on LOW HEAT.

I am glad that the pipe is so short, as a long tall pipe would have had a considerable draft and may have been tougher to deal with.

We had to run to Portland for a few hours and I relit the stove after we returned home and all seems fine.

I am thinking installing a surface mount temp sensor on the outer jacket of the pipe and connect this in with the feed motor circuit to avert another incident.

I am also thinking that I will need to clean the pipe more often, possibly every two weeks instead of monthly.

Just a word to the wise, dont ever think that a pellet stove can't havae a flue fire, THEY CAN.


Snowy

 

[Lousyweather]

Sure can, snowy......some of the deposits are flammable, and you generally get more of them when there is a lower fire (less efficient burn)......so, possibly when you turned it down, you might have gotten more deposits, and when you turned it up, it got hot enough to ignite those same deposits......its good you wree home and had the presence of mind to know what to do, but PROBABLY the deposits would have burned off safely, and had you not been home, you likely wouldnt have known any different. i have seen fires in the pipes so hot they compromised the pipe.....melted the bottom of the tee......much smoke, etc in the house....oh, forgot to say, was a fireman's house......clean the pipe? no

 

[SmokeyTheBear]

I'm sure you are mistaken Snowy.

I have it on good authority from several members of this forum that with a pellet stove such an occurrence is not possible.

Trust them they know, likely your nose and eyes were deceiving you.

Glad everything is fine.

 

[save$]

Glad you are safe. Also glade you didn't find any damage. You had a fire, yet all seems well. Says a lot for the stove, and to your response.

 

[pen]

You did clean this pipe before reassembly correct?

You didn't mention it so I had to ask!

pen

 

[tjnamtiw]

Glad you were so handy and could get to the source quickly! Mounting a snap disk on the pipe is a great idea that maybe everyone should consider.

 

[jtakeman]

Glad all is well and you caught it quickly.

Were still dealing with fire, Even with all the safeties. Things can happen.

 

[Snowy Rivers]

All is well now.

I was just back up to the ranch and siliconed the inner thimble back onto the pipe as I had cut it loose to get access to the inner wall area. (in an hurry too)

I usually never run this stove above the 1 setting and its been an while since I have cleaned the pipe.

I had let the stove run on 2 for about 2 hours so it got a good heating up and finally caught the flue deposits on fire.

While I was home I cleaned the pipe, used the leaf blower on the thing and then carefully inspected the inner stainless steel liner of the pipe.

Nothing apears to be amiss, the pipe shows to be none the worse for the wear.


I dont have any idea if the fire was in the heat exchanger chamber too or just the flue pipe.

On low, even the cast iron outlet assembly on top where the pipe connects only gets warm to the touch, so I can't say for absolute sure.

The exhaust fan blade seems to be in fine shape, and runs true and even with no aparent damage to any of the blades.

Once I get back home again here in about an hour, I will rekindle a fire and let it rip.

Just going to have to be sure to keep the pipe cleaner before cranking things up is all.

The Advantage 2T running on low will have a vent temp of 160F on the side facing into the room.

(The Outer Jacket) and this is measured right where it enters the thimble. This stack is always dry inside.

The little stove runs such a small fire that obviously the vent is running right in the condensate zone and allowing flamables to settle out and stick to the wall.

Right now, there is nothing in the pipe except a little gray dust, and the leaf sucker got most of that.

Just a great learning experience for sure.

Had the fire been allowed to continue, the house would have gotten smoked up some as the paint on the inside section of the vent was just starting to smoke really good when I caught it.

Anyway, all is well for now.

Thanks troops

Snowy

 

[Snowy Rivers]

Life is good

Started the stove back up last night and it is doing fine.

Actually its better than before. May have had a buildup of crap in the heat exchanger unit and the exhaust outlet area.

The exhaust fan is much quieter now too.

Ran the stove all night as usual and everything is sweet.

Just going to practice cleaning the pipe on that stove weekly instead of monthly to prevent any repeat of this scenario.

I ran the stove on the 2 setting this morning for about 30 minutes to heat things up really good and get the vent hot too.

I am going to consider checking into some HIGH TEMP vent pipe.

Seems that somebody makes a High heat Multi fuel pellet pipe.

Snowy

 

[twojrts]

Snowy, so glad you, the house and stove are all ok. That had to be real scarey at first.

Glad the stove is working better than before too.

 

[checkthisout]

Probably safe just to let it burn itself out. I often see flames creeping through the ash in the stove so you know the flyash still has to have some oooommmpphh to it.

 

[Snowy Rivers]

Tell ya what

I was not at all amused by the smoke coming off the pipe in the house.
For one it smells bad, and the pipe has to get pretty hot to burn the paint off.

Just dont like those kinds of supprises, not one bit.

From now on I am amking it a practice to run the stove on a higher setting for a while in the eavening after its been on low all day.

Takes only 30 minutes or so so heat things up well and turn the small accumulations into a NON BURNABLE white/gray ash instead of the dark brown/black soot that can BURN.

Thanks for all the well wishes.

Snowy

 

[heat seeker]

This thread has me thinking about the soot in my pipes, too. I have noticed an accumulation of that brown/black crud in my ash traps, especially since the stove idles more these days. I have started to run it on high for ½ hour every night, and the accumulation is fading away - AND - the stove seems to run a bit better. There is more of the white ash in the traps now, instead of the brown crud.

Then, I cheated! I reread the manual, and it says to do just that - run on high 20 to 30 minutes a day.

Thanks for posting this thread, Snowy, you may have prevented a problem, and my stove is running a bit better now.

 

[Boom]

... From now on I am making it a practice to run the stove on a higher setting for a while in the evening after its been on low all day.

Takes only 30 minutes or so to heat things up well and turn the small accumulations into a NON BURNABLE white/gray ash instead of the dark brown/black soot that can BURN.

I think this is a great idea Snowy! It is how I've kept my chimneys clean of creosote. My old fireplace burned big hot fires every chance I got. When it was inspected the sweep said I must have had it cleaned recently. I told him it was about 15 years ago. hh:

My favorite method of shutting down is to set it to maximum fire with minimum distribution fan then let it run out of pellets. To do this I've made a rectangular metal tube which fits into the hopper opening. I can push it down through pellets so just the pellets within the tube feed into the fire pot. :coolsmile:

 

[arnash]

"I had ASSUMED that the nut shells did not produce creosote, but they do leave a slightly oily residue when burning on LOW HEAT."

So it wasn't an issue of normal pellets stove operation as described in the manual but was related to burning nut shells at a low temp (with slower exhaust air speed?) That leads me to conclude; Pellets and Pellet stove, -Good!, nut shells, -not so good. Say, are nut shells something sold just like pellets? Or do nut shell users live in an area that has nut orchards and they substitute them because they're free or cheap?

 

[Snowy Rivers]

The nut shells are sold in bulk as a waste product right at the processing plants.
Yess, its a local thing. I am in the dump trucking business and can pick up an entire truck load easily.

They are also cheap compared to pellets. Cost me less than $200 to heat the house for the entire season

The issue with the shells the vent fire and such has nothing to do with the shells/fuel but instead the fact that I had run the stove on a low setting for a while an allowed the vent to become coated with a layer of soft "Burnable" fluffy ash.

This can happen just as easily with pellets if you run the stove on a low setting.

I dont need to run that stove for long periods above the low setting, so I need to keep a closer eye on the vent and also turn the thing up once every day or so to burn off the residue.


Many folks consider a vent fire nearly impossible with a pellet stove, not so on any model that allows for a LOW BURN setting.

This little happening was entirely due to two things, having not cleaned the vent in about 3 weeks and having turned the stove up and left it there for close to an hour.

Had I left the stove on low and then cleared the pipe at the usual monthly full deal cleanout there would have been no issues.


Our larger pellet stove, even running on low maintains a higher vent temperature and does not have the issue of the burnables collecting in the vent.


After nearly 20 years of burning nut shells in several different pellet stoves, this is the first such incident, so I dont feel bad.

Just a learning experience is all.

More of an attention getter than a real dangerous condition.

The vent fire was basically out by the time I noticed it and things were already stabilizing, just got to the point that the paint on the inside jacket was starting to give off some smoke.


I have no worries at all about the continued use of the shells, just need to watch that particular stove a tad closer and do vent clearing every two weeks instead of monthly.


Snowy

 

[arnash]

I forgot to ask, about that paint on the inside section of the vent. Did the pipe come painted? Was the paint Hi-Temp spray paint? I'm sure you didn't slap some latex paint on the pipe but I can't guess why vent pipe would be painted except with that black Hi-Temp paint. But I'd also think that that paint would be able to handle that kind of temperature. No?

 

[Snowy Rivers]

The Paint used on the pipe was the HIGH TEMP stove pipe paint.

This paint is designed to handle the normal temperatures found on the outer jacket of the pellet pipe.

If you have a liner fire where the buildup of crap on the inside catches fire and burn, then the temperature of the outer jacket can quickly reach the point that the paint will start to stink.

This pipe came to me already painted.

I got it from a stove shop and it had been used at a "Home show" for a demo setup of a new pellet stove and was painted when I got it.

The dealer discounted the price a B U N C H sooooo as it was just the right length and the price was soooooo good, I took it and then just touched up the paint job and went with it.

My other stove has the pipe left bare. I prefer the pipe being without paint.


Even a new stove will stink some on its first rodeo.

If I paint a stove or as was the case with the new stoves we installed back years ago, I fired them off outside for the first go round and go rid of the "Burnoff" there instead of skunking up the house.

The pipe on the little stove was probably at or near 250-300f when I cuaght it. Hot enough to put a good blister on Y'all

The pipe looks no worse for the wear after the incident.

I cleaned the inner liner well and inspected it well with a bright light.

No signs of "Buckling or warping".

The stainless inner liner is pretty tough stuff.

These pipes are rated at a max flue gas temperature of 570F, but when you lite off a layer of burnables right on the liner the metals temp can rise quickly.

Personally I would like to see a triple wall pipe with a rock wool insulation between the middle metal layer and the room side jacket.

This would assure that what happened during my little incident did not burn off the paint and would not raise concerns about too much heat inside the wall thimble.

Its not at all uncommon to see jacket temps of 200F or possibly more with a stove thats running on a high setting.

The biggy though is to maintain a high enough vent temp to stop flue gases from condensing out and leaving combustibles in the vent.


Snowy

 

[magsf11]

glad to hear that everyone and everything is ok. i just started to burn mine on high about 1/2 hr ago. thaught it was burning on low for some time and that i better crank her up to burn the junk off.

 

[Snowy Rivers]

The practice of running the stove on a high setting for a bit every few days to clear the crap out.

Snowy

 

[SmokeyTheBear]

Jim, I do believe that St. Croix recommends that their stoves be periodically operated on high just for the reason that Snowy ran into.

A lot of stoves when operated on a thermostat in on off mode or in manual mode will actually fire above their normal set firing rate when they start a cold stove for this and other reasons.

 

[Snowy Rivers]

Our Whitfield Advantage 2T can run on low just fine and the vent temps stay high enough that there is not an issue with condensate precipitating out and leaving a "Creosote" type coating in the pipe.

The little Prodigy is a tiny stove and the fire pot is also very small.

The path through the heat exchanger is up and then out around a baffle, then through the exhaust fan and out.

The heat exchanger and the cast iron housing is plenty tough to handle a fire, its the pipe beyond the housing thats the issue.

With the stove on low, the pipe is barely warm to the touch and even the exhaust gas is only warm at 24" from the outlet of the stove.

I had time this morning to watch the operation and came to some conclusions.

Some of the materials in the nut shells are very small and when they hit the fire the "flash" and go out and up into the heat exchanger and on out as "Fly ash". Ok this said, many of these very small particles may not completely burn, but instead flash char and the heat and airflow carry what remains on out and it is then deposited in the pipe.

Pellets too can have small bits that flash over then blow out into the stack/vent.

The higher running temps with the stove on a higher setting will cause this stuff to burn up and not accumulate.

Again, just running the stove on a higher setting and getting the vent temps up will eliminate most, if not all of the issues.

The other method is more frequent cleaning of the vent to prevent buildup.

Snowy

 

[heat seeker]

Jim, I do believe that St. Croix recommends that their stoves be periodically operated on high just for the reason that Snowy ran into.

My Afton Bay manual recommends 20 to 30 minutes on high - every day. It does make a difference, since mine pilots quite a bit, and a brownish crud collects in the ash traps and the vent. Running on high gets rid of that. I don't know if that crud is flammable, but the stove does breathe better since I've started doing that. Therefore, running on high for 30 minutes is now part of my daily routine.

 

[ChandlerR]

Snowy, I'm glad all is well. If you remember, I had the same issue last spring when my wife turned the stove up to 3 after running it on1 for a couple of weeks. With the vertical rise I have the gasses cool enough to form creosote at the end cap. We now run the stove on 3 every time we start it for 1/2 hour, no matter how warm the room gets. I don't want to get that panicked call at work again that I have a chimney fire!

By the way, since we have instituted the new policy, the pipe has been very clean, just some fine ash.

 

[Snowy Rivers]

Yess indeed.

Now when I get up in the morning at around 5am I start the coffee, fill the hopper with shells, clean the clinker out of the fire pot real quick then kick the stove on the number two (2) SETTING for about 30 minutes or so.

Gets the little short vent nice and hot, and the inside turns a whitish gray.

The other day was double bad because we had to head out really early to Portland for a doctors apptmnt that could not be broken.

shut the stove off really quick, removed the inner part of the thimble so I could check to see how hot things got up in the wall.

Just left the beast off until we got home and then relit the fire.


I dont take chances with these things, gotta be right.


Snowy