Pellet stove hopper fires?

[freebird77]

I had a friend tell me that due to the type of auger feed system in the Harmon pellet stove, if there were a power shortage, it possible for the fire to continue burner backwards following the auger and ignite the pellets in the hopper. Have any of you heared of this, and done it seem possible? I havent even used my new p61 yet, and now am a bit concerned about what he said. Help, advice, anyone, is greatly appreciated. thank you

 

[GVA]

NO not likley
What happens when you shut the stove down?
Now think about what happens when the power goes out? Nevermind just reread the post and yu haven't even fired it up yet.
but these still apply..

Fire needs O2 and since there is no O2 because the combustion blower is off there will be a lot of smoldering thus choking off the fire ETC. ETC. ETC

So with that in mind make sure your gaskets are good and ......... Make sure the hopper door is closed and latched while running

 

[stoveguy2esw]

GVA is exactly right , if the hopper is sealed and the stove is properly installed (vented correctly) the fire should not be able to travel where there is no airflow, essentially it will smoulder out what is in the pot and go out with the smoke travelling out through the vent.

 

[freebird77]

Thanks, Thats kind of what I thoguht. Although it has the fresh air line running outside, so I wondered if that would give it enough oxegyn to keep going

 

[wg_bent]

The stove Mike sells (Englander's) use a similar auger feed to the Harman. I'm guessing they tested that a time or two to see what happens. If the whole thing caught fire, my guess is that they wouldn't be selling Pellet stoves.

The big advantage of the bottom auger feed is that you don't hear the constant "plink plink plink" of pellets falling into the burn pot.

 

[iceman]

in EXTREME cases it could happen but there is always something that someone did wrong ie worn gaskets etc etc ... the stove won't just do it
for example.... you have very very bad gaskets and you auger slide broke and then you lost power... see what i mean more than the power going out has to go wrong.... so don't worry pound for pound harman makes some of the best pellet stoves out there

 

[GVA]

Thanks, Thats kind of what I thoguht. Although it has the fresh air line running outside, so I wondered if that would give it enough oxegyn to keep going

It shouldn't cause there is a flapper in there too.. so again no blower the flapper should stay closed or close to it.
also the auger is about a foot long and it would be unlikely for the smoldering flames to burn past the 3rd flight (theres about 6 on the auger).
You could also buy a UPS and make sure your stove keeps chugging along through the power failure... ;-)

 

[Corie]

Generally the only time we've ever seen burn back into the hopper occur was when a VERY VERY poor maintained stove suffered a power outage AND the hopper door was left wide open. There's a lot more operator error at fault in that case than an actual design flaw in the stove.

 

[freebird77]

Thank you all for the reassuring thoughts. My friend tends to exagerate sometimes and he probably heared about one freak inncident or something, just enough to cause me some concern. You folks are great. Cant wait to try out the stove, which wont be long now.

 

[Corie]

You'll be very pleased with the Harman unit! How about some photos eh?

 

[BIGISLANDHIKERS]

I see on another forum there is a case of a quadafire AE hopper fire. Not sure If I am allowed post the link to the forum but here is a link to the pics of the stove.

http://www.thewoodscc.com/gallery/main.php?g2_itemId=5487

Thanks!
BIH

 

[HarryBack]

I guess its theoretically possible to create a hopper fire, but I think it far more likely that you'd have to force it to burnback. How would we do this? Well, id put a small amount of pellets in the hopper, leave the lid open, close the intake damper off tight, thusly forcing the stove to attempt to pull air through any available inlet (the hopper, in this case)...then id have to either turn the auger off, so it doesnt drive, or set it at a VERY low feed rate. Also, it would help if we had the benefit of natural draft (stove plumbed into a chimney that sucks REALLY well), and this would create a natural draw, dragging possible combustion air into the hopper....


Ive also heard the stories of a greater chance of hopper fires, but fell its more likely propagated by other manufacturers who use the inclined auger method of fuel delivery.

And the main advantage for an underfire fed system is the fact that they tend to require much less frequent care, in that they ten d to clear their burnpot much better than inclined auger systems. But, then, I sell the Harmans, so I might be biased.

 

[begreen]

Agreed there is a bit of sales propaganda here on all sides. 5 years of running the top auger, Quad 1200i and there was never an auger problem. And I cleaned the burnpot once every two weeks. As long as I was burning good fuel, the cleanout was minimal.

 

[BIGISLANDHIKERS]

I own the Quadrafire AE and love it! I know there have been issues with it but once worked out it is a great stove. I have heard of two recent cases of hopper fires in the AE. Nobody on this other forum have been able to pin down what the causes were. I want to be able to run this stove when I am at work so I am very curious in the cause(s)

BIH

 

[GVA]

I own the Quadrafire AE and love it! I know there have been issues with it but once worked out it is a great stove. I have heard of two recent cases of hopper fires in the AE. Nobody on this other forum have been able to pin down what the causes were. I want to be able to run this stove when I am at work so I am very curious in the cause(s)

BIH

With a screen name like dmecoal..........
I hope he didn't try to mix some rice coal or other stuff in with his pellets.....
If not I would thing that maybe some type (probably improper) of accellerant was used to start it up quicker and maybe the flames burned up to high or vapors rose into the hopper. But that is not an under feed stove in the pic

 

[webbie]

Back when I sold pellet stoves, there were some burn back situations. I assume most of these were solved by redesign. In my opinion, the Harman and similar designs are less likely to burn back because (as I remember), the pellets are pushed over a "cliff" and then picked up by the auger, so it would be tough for there to be a bridge back to the hopper.

The situations I ran into were not nearly as bad as that pic! Usually, it was just smoke coming from the hopper and the customer would notice and shut the stove down - and open the windows. As I remember they were top fed units....the pellets built up in the burn pot (not cleaned by the customer) and eventually went back - the auger may have also jammed or perhaps the stove shut down and then the burn back continued.

 

[jtp10181]

I see on another forum there is a case of a quadafire AE hopper fire. Not sure If I am allowed post the link to the forum but here is a link to the pics of the stove.

http://www.thewoodscc.com/gallery/main.php?g2_itemId=5487

Thanks!
BIH

I have worked on the other Quadrafire units, and also worked some on this new AE unit. I have also talked to people who investigate these kinds of cases. Most of the hopper fires with the Quadrafire gravity feed system is from extreme lack of maintenance or misuse. If the burn pot is allowed to fill up completely with burnt fuel and clinkers then the pellets will make a sort of bridge to the feed tube. At this point the feed tub starts to fill up and jam. Now there is a path of fuel from the burn pot to the hopper and once it all starts burning away it goes. It really helps it go if the hopper lid is open. On all the Quad units the auger tube should have a safety hi-limit switch on it that shuts the whole unit down if it gets tripped.

Someone mentioned that hopper fires are more common with this gravity feed system? The pellets are dropped out of the auger and are totally separated from the burning pellets. On the bottom feed units from what I understand the pellets are just pushed right into the fire. I'm sure there is some way it is separated from the fire? It seems that logic would say it would be easier for a hopper fire in this case but I have never seen one of these systems up close so I can;t say how they work exactly.

 

[webbie]

There are different types of bottom feed. On top feed, as you mention, as soon as the pellets stack up in the pot they can head back up the auger tube - to say nothing of the fact that that is upward (draft)....

But I remember the Harman mechanism working like so:

a little pusher block moves back and lets some pellets fall onto a shelf.
The same block comes back and then pushes them over a cliff
then, at the bottom of the cliff they are picked up by the auger.

if this is correct (and I am going by the VC design, which was a Harman guts), then it is almost impossible for the pellets to bridge back, because of the ledge they fall over....only a little at a time. Perhaps harryback can confirm or deny this.

 

[GVA]

There are different types of bottom feed. On top feed, as you mention, as soon as the pellets stack up in the pot they can head back up the auger tube - to say nothing of the fact that that is upward (draft)....

But I remember the Harman mechanism working like so:

a little pusher block moves back and lets some pellets fall onto a shelf.
The same block comes back and then pushes them over a cliff
then, at the bottom of the cliff they are picked up by the auger.

if this is correct (and I am going by the VC design, which was a Harman guts), then it is almost impossible for the pellets to bridge back, because of the ledge they fall over....only a little at a time. Perhaps harryback can confirm or deny this.

Can't speak for HB but I think that was the old coal stoker version.
The pellet versions of today are a mechanicly interlocked slide plate and auger.
I'll let him field this he can explain it far better than I.......(and with less space )

 

[HarryBack]

Craig and GVA are both right. In the early PelletPro Harman models, the stove indeed did use a pusher block rather than an auger....with the advent of the Invincible line (no longer produced), the auger feed system came into use in the Harman line.

Basically, the pellets fall through a small hole in the hopper base, landing on the slide plate, which is slowly moved back and forth, dropping the pellets a few inches onto the auger, which turns and is propelled into the burnpot. Ill take a few pics of a display model I have and will post accordingly here later.

 

[jtp10181]

So the auger is basically IN the fire and kind of stirring it at the same time? And the pellets get into the back of the auger by this slide plate that pushes them off a ledge. Sounds like it would work just fine.

 

[HarryBack]

So the auger is basically IN the fire and kind of stirring it at the same time? And the pellets get into the back of the auger by this slide plate that pushes them off a ledge. Sounds like it would work just fine.

The tip of the auger could be very close to, if not actually touching the fire, but the lions' share of the auger isnt IN the fire.