Thanks for the link, although I don't believe this is the problem since it happens even on very still days.BLIMP said:
Potential Cure for Back-Puffing?
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>:-( Hmmpf. I would be irritated as well. I think its time to get your dealer front and center on this one. It does sound like the stove is acting funny (and not in a Leslie Nielsen sort of way). If you have a full fuel load, crank it up and touch nothing, it will die out with plenty of fuel left?? Am I getting that right?
I found my problems with my stoves although not backpuffing per say but were caused by excess draft and the stove keeping up to the draft. Pipe damper smoothed everything out only need it several times a year.
My guess is that in this case, excessive draft is not the problem; it seems like not enough draft, but only with the CAT engaged. I would guess that it may be more of a problem with the stove (I still haven't ruled out operator error).ddown said:
Diabel
Minister of Fire
I would remove the back shield remove the small thermo. shield & see if it is shut closed (when the stove is cold)... it could be your problem. The only way I have experienced back puffing with these stoves is when you cut back the air too fast while in the secondary mode.
Thanks for the suggestion; I'll take a look at that tonight.Diabel said:
Last night I experienced some back-puffing even though I hadn't reduced the air one bit. I find it strange that the wood was smoldering with the air control wide open (with the CAT engaged). Without the CAT engaged, the fire was absolutely blazing; in fact it would have been over-firing if I didn't either reduce the incoming air, or engaged the CAT. So for this reason, I don't think it is a draft problem. In my mind, it can be one of three possibilities:
1) malfunctioning thermostat
2) defective CAT
3) really bad design (don't think this is the issue, but some others have had similar problems)
Diabel
Minister of Fire
VC stoves will back puff more than others due to design (this is from what I have read here) but with properly seasoned wood & gradual air reduction it should not back puff at all.
grommal
Feeling the Heat
Tried kiln dried wood with mine. Backpuffing no matter how slowly the air was backed down, and sometimes without even backing it down at all. Believe me, I tried everything as far as operational variables. I'm a scientist/engineer with decades of R&D experience, and I know how to study multiple variables and their impact. Our VC was a 23 year failed experiment.Diabel said:
webbie
Seasoned Moderator
Diabel
Minister of Fire
grommal said:
Hm....these stoves (defiants) are all built the same the only difference is each flue set up....therefore perhaps the flue is responsible for this...
Diabel said:
Yet it also seems like most of the posts on continual, unexplained backpuffing are coming from folks with Defiants - myself included. Although, we could all have the same incorrect flue set up for the stove. We have 24 ft of straight 8" pipe at our place.
Found this: Seems to be related to wood and burning technique
http://www.chimneys.com/burning_secrets/chapter_5.html
Backpuffing:
Backpuffing is essentially small explosions in the stove, forcing puffs of smoke into the room through every available gap in the stove or stovepipe. It is caused by a combination of reduced airflow into the stove and use of too-dry wood or wood that's split so small that it burns too rapidly. Instead of the gasses burning as they are emitted, they collect in the firebox. Oxygen slowly enters the firebox, and when there is finally enough, the gasses ignite.
The problem of backpuffing is also a good reason not to burn things like kiln- dried wood blocks, pallets, and trimmings from woodshops, except as kindling.
Tip #3: Learn the right way to build a fire. If you are not a seasoned firebuilder, see How to Build a Fire, page 15. In a woodstove, the trick is to use enough kindling and small splits of wood to establish a bed of coals quickly, then to add larger logs.
Tip #4: Avoid long, low fires. Especially if you have an "air-tight" stove, avoid low, smoky fires. Yes, long burn time is a convenience. But believe it or not, you are getting much less heat from your wood if the fire is smoky.
Jets of smoke emitted from a wood stove, caused by the ignition of a buildup of combustible gasses in the firebox.
In short, backpuffing is caused by an inadequate flow of oxygen into the firebox. Instead of burning steadily, combustible gasses build up in the firebox and periodically ignite in a small explosion, forcing smoke out of the stove through every available opening, including the air intakes.
What might cause your stove to backpuff?
Generally, shutting the air controls down too far, starving the fire of oxygen, AND:
either Using super-dry wood, like pallets or kiln-dried wood blocks, which burn very rapidly, emitting too much combustible gas too quickly. (See page 53 for details.)
or Using firewood that is split very small, which also burns too rapidly, creating an excess of combustible gas in the firebox.
Backpuffing is fairly easy to diagnose: Try opening the air control on the stove. If the smoking stops, it is very likely a backpuffing problem. Of course, you shouldn't over-fire the stove, either. If you have to open the air control to the point that the stove will overheat before the backpuffing stops, then reconsider your firewood supply. Either get a new load of properly-seasoned wood, or try mixing less- dry or larger pieces with the super-dry or small-cut pieces. (See page 52 for details on firewood selection.)
http://www.chimneys.com/burning_secrets/chapter_5.html
Backpuffing:
Backpuffing is essentially small explosions in the stove, forcing puffs of smoke into the room through every available gap in the stove or stovepipe. It is caused by a combination of reduced airflow into the stove and use of too-dry wood or wood that's split so small that it burns too rapidly. Instead of the gasses burning as they are emitted, they collect in the firebox. Oxygen slowly enters the firebox, and when there is finally enough, the gasses ignite.
The problem of backpuffing is also a good reason not to burn things like kiln- dried wood blocks, pallets, and trimmings from woodshops, except as kindling.
Tip #3: Learn the right way to build a fire. If you are not a seasoned firebuilder, see How to Build a Fire, page 15. In a woodstove, the trick is to use enough kindling and small splits of wood to establish a bed of coals quickly, then to add larger logs.
Tip #4: Avoid long, low fires. Especially if you have an "air-tight" stove, avoid low, smoky fires. Yes, long burn time is a convenience. But believe it or not, you are getting much less heat from your wood if the fire is smoky.
Jets of smoke emitted from a wood stove, caused by the ignition of a buildup of combustible gasses in the firebox.
In short, backpuffing is caused by an inadequate flow of oxygen into the firebox. Instead of burning steadily, combustible gasses build up in the firebox and periodically ignite in a small explosion, forcing smoke out of the stove through every available opening, including the air intakes.
What might cause your stove to backpuff?
Generally, shutting the air controls down too far, starving the fire of oxygen, AND:
either Using super-dry wood, like pallets or kiln-dried wood blocks, which burn very rapidly, emitting too much combustible gas too quickly. (See page 53 for details.)
or Using firewood that is split very small, which also burns too rapidly, creating an excess of combustible gas in the firebox.
Backpuffing is fairly easy to diagnose: Try opening the air control on the stove. If the smoking stops, it is very likely a backpuffing problem. Of course, you shouldn't over-fire the stove, either. If you have to open the air control to the point that the stove will overheat before the backpuffing stops, then reconsider your firewood supply. Either get a new load of properly-seasoned wood, or try mixing less- dry or larger pieces with the super-dry or small-cut pieces. (See page 52 for details on firewood selection.)
webbie
Seasoned Moderator
Here is our own little entry on the same:
https://www.hearth.com/econtent/index.php/wiki/flashback/
As to chimneys and stove models, here is the deal IMHO. Stoves are generally tested in a lab with a certain chimney...especially after EPA, they are tested so that they pass the test with low numbers. Sadly, that type of testing does not always approximate all the variables involved with different chimney types, weather conditions, wood species and moisture, operation, aging of the stove, etc.
So, would I say some VC models historically have reported more of this? Yes. I used to hear the complaint even about some Dutchwest models back when I sold them.
Would I say it is a design defect? Probably not in those terms. However, I think various things in combination contribute to the problem. It seems catalytic stoves are more prone to this - my guess is because they are often designed to somewhat smolder the wood and then burn it up in the cat. That works fine mostly...but at certain times in the cycle the flow is not consistent and might result in excess smoke buildup inside the stove...which is then ignited by the cat.
Each situation is different, but I would personally try some of the following - depending on stove model:
1. Turn damper - this can be used to slightly choke off the draft - you might find a setting that is right, set it and forget it.
2. Barometric damper - install upstream (toward chimney) from the turn damper if you use both.
3. Method to make sure plenty of idle air is available - this might entail a paper clip of some other way of making sure a primary air damper does not shut down too tight.
https://www.hearth.com/econtent/index.php/wiki/flashback/
As to chimneys and stove models, here is the deal IMHO. Stoves are generally tested in a lab with a certain chimney...especially after EPA, they are tested so that they pass the test with low numbers. Sadly, that type of testing does not always approximate all the variables involved with different chimney types, weather conditions, wood species and moisture, operation, aging of the stove, etc.
So, would I say some VC models historically have reported more of this? Yes. I used to hear the complaint even about some Dutchwest models back when I sold them.
Would I say it is a design defect? Probably not in those terms. However, I think various things in combination contribute to the problem. It seems catalytic stoves are more prone to this - my guess is because they are often designed to somewhat smolder the wood and then burn it up in the cat. That works fine mostly...but at certain times in the cycle the flow is not consistent and might result in excess smoke buildup inside the stove...which is then ignited by the cat.
Each situation is different, but I would personally try some of the following - depending on stove model:
1. Turn damper - this can be used to slightly choke off the draft - you might find a setting that is right, set it and forget it.
2. Barometric damper - install upstream (toward chimney) from the turn damper if you use both.
3. Method to make sure plenty of idle air is available - this might entail a paper clip of some other way of making sure a primary air damper does not shut down too tight.
stoveguy2esw
Minister of Fire
most cat stoves have an air bleed (secondary air source) located in close proximity to the underside of the cat , you might see if you can locate this opening and ensure its not restricted. backpuffing can be caused by a "low order explosion" so to speak, of combustibles which build up waiting for a puff of air , when the fresh air does get to it the "explosion" creates pressure which forces out in whichever direction it can get to. ive seen cat stoves with plugged secondary inlets do this in the past. this can happen with a perfectly servicable catalyst by the way.
UPDATE: I had another VC dealer come over to check out my setup; he said that the problem is most probably a draft issue and that there were several potential issues:
1) Use of 6 inch flex liner: he said that the Defiant absolutely requires an 8 inch liner (notwithstanding what VC states in their brochure); he believes this is the main culprit
2) Chimney height not enough above roof: the chimney is 20 feet high but only about a foot and a half above the roof
3) Exterior chimney: the chimney is actually interior/exterior, where half of it is inside and half outside
4) Cathedral ceiling which may compete with chimney for draft
I then spoke to the Chimney sweep who ultimately agreed to replace my liner with 8 inch stainless. He also insulated it all the way up and installed a block-off plate at the bottom of the chimney. The sweep believes this will make a big difference, but is concerned about the top of the chimney being less than two feet from the top of the roof. He would want to extend it about two feet higher, but it would cost around $2K to do so due to the stone work to extend the chimney (and the need to setup scaffolding).
Anyone have a feeling on the whether extending the chimney an additional two feet will make a big difference? I want to get the whole system it to perform as well as possible, but $2K for two feet of chimney extension is a lot of money!
1) Use of 6 inch flex liner: he said that the Defiant absolutely requires an 8 inch liner (notwithstanding what VC states in their brochure); he believes this is the main culprit
2) Chimney height not enough above roof: the chimney is 20 feet high but only about a foot and a half above the roof
3) Exterior chimney: the chimney is actually interior/exterior, where half of it is inside and half outside
4) Cathedral ceiling which may compete with chimney for draft
I then spoke to the Chimney sweep who ultimately agreed to replace my liner with 8 inch stainless. He also insulated it all the way up and installed a block-off plate at the bottom of the chimney. The sweep believes this will make a big difference, but is concerned about the top of the chimney being less than two feet from the top of the roof. He would want to extend it about two feet higher, but it would cost around $2K to do so due to the stone work to extend the chimney (and the need to setup scaffolding).
Anyone have a feeling on the whether extending the chimney an additional two feet will make a big difference? I want to get the whole system it to perform as well as possible, but $2K for two feet of chimney extension is a lot of money!
Thanks for the suggestion; I'm surprised the sweep didn't mention it. Any idea on what this costs for a two foot extension? The only potential issue is one of aesthetics; I currently have a flat slate slap on top of the chimney; I suppose the extendaflue would need a standard cap?BeGreen said:
You can extend your flue 2' without building the masonry chimney higher for a whole lot less than $2K, so long as you don't mind seeing a couple feet of Class A chimney pipe (either galvanized or polished stainless) sticking up above the top of the existing masonry. Rick
ETA: As usual, BeGreen was a step ahead of me.
ETA: As usual, BeGreen was a step ahead of me.
Up there, does it even need to be class A? Cheap fix would be add 2 ft of rigid stainless liner.
BeGreen said:
Well, interesting question. I always thought that once you went Class A, you stayed that way to daylight. Maybe if you're talking about just extending a liner past the top of the masonry chimney structure you don't need it. I'm probably stuck in the stovepipe/chimney mindset, as I don't have anything that runs a liner. Rick
Doesn't it need to be insulated? It may not look great to see a metal pipe sticking above the chimney, which has some nice stonework.fossil said:
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