Potential Cure for Back-Puffing?

[Gridlock]

Could installing an outside-air kit potentially cure back-puffing problems?

 

[Todd]

It's a good possibility if you have a negative pressure problem. Good way to check is to burn the stove with a nearby window open to see if it corrects the backpuffing. Does your Defiant have a thermostatic coil? Maybe it's stuck or broke?

 

[Gridlock]

It's a good possibility if you have a negative pressure problem. Good way to check is to burn the stove with a nearby window open to see if it corrects the backpuffing. Does your Defiant have a thermostatic coil? Maybe it's stuck or broke?

My house is fairly leaky, but haven't tried burning with a window open. The folks at chimneysweeponline.com thought that adding the outside-air kit might solve the back-puffing problem.

The Defiant has two thermostatic air vents; one for the main firebox and the other for the secondary catalytic chamber. Interestingly the main air control seem very sticky when I turn it to adjust the air input; the chimney sweep will take a look when he comes next week. Thanks for the suggestion.

 

[Patapsco Mike]

Backpuffs are from the rapid combustion of unburned gasses in the firebox, and tend to happen when your draft is poor. I could see how a cold-air return might help in some cases, but I do not see how insulating one would change your draft in any way.

 

[Jags]

Sounds like a draft issue to me as well. You have already been introduced to one method (OAK), but if you still need a little help, don't forget the other end (the part pointing to the sky). Years ago - my installation would, on occasion, get air rushing down the pipe. It was cured with a simple two foot addition to the top of the stack. You can cheaply test this with a section of the tin duct work from any home store. For a few bucks and a couple of minutes on the roof, you will know if this solves the problem. If it does, then pony up the bucks for the real stove pipe.

Also - if you have a cap on the top, don't overlook that. Take a good look at it and make sure it is not getting plugged up.

 

[Backwoods Savage]

At one time we had an OAK on one stove and burned it like that for several years. We did have back-puffing off and on, mostly prior to a storm or in windy conditions. After a time we removed it and noticed no difference.

Our next stove we hooked up w/o the OAK and had some backpuffing so as Jags stated above, we raised the chimney a bit (2') and it helped but did not take away totally. We always thought it is because we are surrounded by tall trees.

When we installed our last stove we also put up a new SS chimney. The stovepipe runs straight out the back and through the wall (1/2" raise per foot of horizontal pipe) then up on the outside, this time about a foot higher. We have had maybe 2 backpuffs in 3 years and they were very minor.

So, it may or may not help to install an OAK.

Good luck.

 

[grommal]

Not all back-puffing issues can be traced to poor draft. We used to have terrible back-puffing with our old stove, yet when you opened the bypass around the cat, it would run away instantly because of the strength of the draft that was already present. Plus, with our new stove, there seems to be zero tendency to puff, and enough draft to start the stove from cold with all the doors closed. Nothing on the chimney was changed. Only the stove.

 

[madison]

grid,

Does opening the primary air prior to opening the stove door change the amount of back puffing? And does the outdoor temperature make any difference with your problem?

 

[ddown]

Could installing an outside-air kit potentially cure back-puffing problems?

I've been following you backpuffing/New stove saga. I'd wait until sweep/shop checks out your setup. I traded a couple stoves before I figured out part of problem was a bad section of class A not sealing and wood quality could have saved about 5 grand and had the Stove I originally bought. Your assuming it's the stove have it checked first. My dealer missed it first three trips until I got pictures during a burn.

 

[Gridlock]

Not all back-puffing issues can be traced to poor draft. We used to have terrible back-puffing with our old stove, yet when you opened the bypass around the cat, it would run away instantly because of the strength of the draft that was already present. Plus, with our new stove, there seems to be zero tendency to puff, and enough draft to start the stove from cold with all the doors closed. Nothing on the chimney was changed. Only the stove.

This is exactly the situation. I have no problems starting and maintaining the fire with the damper open; in fact with it open, the stove top temperature gets very hot fast, and I have to close the air control almost all the way to prevent it from over firing. Yet, when I close the damper to engage the cat, it seems to work Ok for a while, but am soon in the same situation with back-puffing, even with the air control open wide open. With the air control closed down somewhat, it starts back-puffing badly. This happened again tonight. The stove top temperature drops, and the cat chamber temperature rises rapidly to 2200 degrees. It is worse if I close the air control as this will produce more smoldering/smoke which will increase the cat temperature even more and cause back-puffing.

I do wonder if one of the thermostats is not working properly causing this problem.

 

[Gridlock]

grid,

Does opening the primary air prior to opening the stove door change the amount of back puffing? And does the outdoor temperature make any difference with your problem?

Opening the air control does help reduce back-puffing, but does not cure it. Not sure what you mean about opening the door as a cure for back-puffing.

The issue does seem worse with outside temperatures that are not as cold.

 

[Gridlock]

Could installing an outside-air kit potentially cure back-puffing problems?

I've been following you backpuffing/New stove saga. I'd wait until sweep/shop checks out your setup. I traded a couple stoves before I figured out part of problem was a bad section of class A not sealing and wood quality could have saved about 5 grand and had the Stove I originally bought. Your assuming it's the stove have it checked first. My dealer missed it first three trips until I got pictures during a burn.

Thanks; the chimney sweep is coming Monday to check things out. The funny thing is that he seems to almost not want to deal with it and give my money back. We'll see. As I mentioned in another post, I do wonder if it could be a problem with one of the thermostats. The air control is quite sticky and scratchy when moved, and that is connected directly to the main thermostat. I also wonder if having a 6" flue instead of an 8" is part of the problem. VC mentions a 6" can be used but does not recommend using it this way in fireplace mode (doors open with screen).

 

[fbelec]

how many feet is your chimney? sorry. how tall is your chimney?
how long are you waiting to engage the cat?
what temp is the stove top when you engage?
if your cat is burning that hot you might want to engage a little sooner when the temp is lower and let the stove do it's thing a little slower. it's worth a try.

 

[SolarAndWood]

I also wonder if having a 6" flue instead of an 8" is part of the problem. VC mentions a 6" can be used but does not recommend using it this way in fireplace mode (doors open with screen).

I had a lot of problems with my VC cats but back puffing was not one of them even when it was milder out. I have a straight up 8" triple wall stack.

 

[madison]

grid,

Does opening the primary air prior to opening the stove door change the amount of back puffing? And does the outdoor temperature make any difference with your problem?

Opening the air control does help reduce back-puffing, but does not cure it. Not sure what you mean about opening the door as a cure for back-puffing.

The issue does seem worse with outside temperatures that are not as cold.

Maybe I am misunderstanding "back puffing". I was thinking that "back puffing" was smoke entering the room from the stove while opening the stove door , ie for reloading... Is "back puffing" something other than that?

 

[begreen]

Yes, backpuffing is a mini-explosion of unburnt wood gas that is often strong enough to force smoke out of pipe seams, past door and top lid gaskets. A big backpuff is something you won't forget. I had a big one while learning about the Castine. It was my fault. I was impatient and had a balky starting fire on which I put too large splits before the kindling bed has a good chance to get going. The fire snuffed out after a few minutes and filled with smoke. Stupid me cracked open the ash pan door to get it quickly started. The moment a flame caught, it ignited the unburnt wood gasses with a mighty whumpf!

It's moments like these when you are very glad the flue has 3 screws per joint and that the stove is well made. I actually looked outside to be sure the cap stayed on. Needless to say I never did that again and stopped ever trying to start the fire using the ash pan door.

 

[Jags]

Yes, backpuffing is a mini-explosion of unburnt wood gas that is often strong enough to force smoke out of pipe seams, past door and top lid gaskets. A big backpuff is something you won't forget. I had a big one while learning about the Castine. It was my fault. I was impatient and had a balky starting fire on which I put too large splits before the kindling bed has a good chance to get going. The fire snuffed out after a few minutes and filled with smoke. Stupid me cracked open the ash pan door to get it quickly started. The moment a flame caught, it ignited the unburnt wood gasses with a mighty whumpf!

It's moments like these when you are very glad the flue has 3 screws per joint and that the stove is well made. I actually looked outside to be sure the cap stayed on. Needless to say I never did that again and stopped ever trying to start the fire using the ash pan door.

+ 1000 :sick:

You won't forget that sound.

 

[fbelec]

Yes, backpuffing is a mini-explosion of unburnt wood gas that is often strong enough to force smoke out of pipe seams, past door and top lid gaskets. A big backpuff is something you won't forget. I had a big one while learning about the Castine. It was my fault. I was impatient and had a balky starting fire on which I put too large splits before the kindling bed has a good chance to get going. The fire snuffed out after a few minutes and filled with smoke. Stupid me cracked open the ash pan door to get it quickly started. The moment a flame caught, it ignited the unburnt wood gasses with a mighty whumpf!

It's moments like these when you are very glad the flue has 3 screws per joint and that the stove is well made. I actually looked outside to be sure the cap stayed on. Needless to say I never did that again and stopped ever trying to start the fire using the ash pan door.

+ 1000 :sick:

You won't forget that sound.

or sight

 

[Jags]

Yes, backpuffing is a mini-explosion of unburnt wood gas that is often strong enough to force smoke out of pipe seams, past door and top lid gaskets. A big backpuff is something you won't forget. I had a big one while learning about the Castine. It was my fault. I was impatient and had a balky starting fire on which I put too large splits before the kindling bed has a good chance to get going. The fire snuffed out after a few minutes and filled with smoke. Stupid me cracked open the ash pan door to get it quickly started. The moment a flame caught, it ignited the unburnt wood gasses with a mighty whumpf!

It's moments like these when you are very glad the flue has 3 screws per joint and that the stove is well made. I actually looked outside to be sure the cap stayed on. Needless to say I never did that again and stopped ever trying to start the fire using the ash pan door.

+ 1000 :sick:

You won't forget that sound.

or sight

I never saw mine, my back was turned. But I never thought I would hear the sound of my 460 pound stove jumping off the floor either. It did. It literally jarred the whole house.

 

[Gridlock]

how many feet is your chimney? sorry. how tall is your chimney?
how long are you waiting to engage the cat?
what temp is the stove top when you engage?
if your cat is burning that hot you might want to engage a little sooner when the temp is lower and let the stove do it's thing a little slower. it's worth a try.

My chimney is somewhere between 23 and 26 feet (I measured it the other day but don't remember exactly). The chimney is stone on the outside, about 2/3 of which is inside the house, and the other 3rd juts outside past the exterior wall. The stove sits just outside the fireplace, so the stove pipe runs horizontally for 1 or 2 feet into a T fitting, then runs straight up the chimney. The pipe is 6".

I've experimented a lot with waiting times and temperatures. Last night I let it run for almost 1.5 hours until most of the wood burned and there was a thick bed of hot coals. The griddle temperature at that point was about 600-650 degrees. I then loaded it with several splits (about 2/3 filled), let it run for about 10 minutes with the damper open and the air control on maximum, then closed the damper. For the first 45 minutes or so, everything was fine. Then whatever fire there is dies down, and the back-puffing starts. This is with the air control still at maximum. If I lower the air control, the back-puffing gets much worse. The CAT chamber temp is also reading very high, over 2,000 degrees. After another hour or so, things improve; there is a fire in the box, the smoke dies down as the wood burns, and the CAT chamber temp drops. At this point I can lower the air control substantially, and everything seems to run Ok from that point.

I've also tried running the stove for less time before engaging the CAT, engaging the CAT when the stovetop temperature is lower (around 500-600 degrees for example), using smaller or larger splits, and doing a native american dance, but I can't seem to find any consistency.

As I mentioned earlier, I do wonder if there is either a problem with the main thermostat, a bad gasket, or some other problem. VC recommends either a 6 or 8 inch pipe; they only limitation for the 6" pipe is not being able to run the stove with the door open (fireplace mode). I do wonder if the 8" pipe will work better, although I have absolutely no problems with starting or running the stove without the CAT engaged.

 

[Jags]

Plugged CAT? (just thinking out loud).

 

[Gridlock]

Plugged CAT? (just thinking out loud).

Good thought. I inspected and cleaned the CAT 3 times already within the past couple of months thinking that that may be the problem, but it didn't make a difference. The last time I cleaned it (on the advice of someone at Woodstock Stoves who was very helpful even though I don't have a Woodstock stove) I used a can of compressed air to flush any ash that might have plugged some of the honeycomb. I also used my vaccuum. The CAT appeared very clean, and it does light up (actually too well, as I've seen CAT chamber temps up to 2,200 degrees (although I believe the Condar guage is reading too high)!

 

[Jags]

Just revisiting a few things to stir up thoughts.

Back puffing happens because of un-burnt volatiles in the stove or pipe being in a state of non-combustion then having oxygen and ignition re-introduced.

The stove appears to draft well with the cat by-passed. Check!

The fuel appears to be seasoned and ignites well. Check!

You get periods of "proper" burn when cat is engaged, but then will die back to a state where back puffing occurs.

Hey - when this back puffing happens - can you visually see the direction it goes. Does it puff UP or do you see a rush of air coming DOWN?

 

[Gridlock]

Just revisiting a few things to stir up thoughts.

Back puffing happens because of un-burnt volatiles in the stove or pipe being in a state of non-combustion then having oxygen and ignition re-introduced.

The stove appears to draft well with the cat by-passed. Check!

The fuel appears to be seasoned and ignites well. Check!

You get periods of "proper" burn when cat is engaged, but then will die back to a state where back puffing occurs.

Hey - when this back puffing happens - can you visually see the direction it goes. Does it puff UP or do you see a rush of air coming DOWN?

I looks like it is puffing upward.

By the way, there are varying degrees of severity with this problem. Last night the back-puffing wasn't severe enough where lots of smoke was getting into the house, just a bit; probably because I didn't back off on the air control. At other times, the back-puffing got severe enough where you can hear the explosions more loudly, and you can see large amounts of smoke forcing past the loading door on top of the stove. In both cases, you see the distint sudden bursts of flame in the stove.

What's strange is why the fire dies down so completely even with the air control wide open. When things are working right, there will be a visible fire if the air control is wide open even with the CAT engaged. For some reason the fire, which starts out blazing and very hot (stove top temps of between 600 and 700) dies down to a smolder even with the air control wide open. This is why one theory I have is that the thermostat is not working properly and keeping the air door closed even though the air control itself is set on maximum. What I may do is remove the heat shield in the back of the stove so I can observe what is happening with the air openings. The heat shield is not really necessary; it was installed with the thought of forcing more heat forward away from the inside of the fireplace.

 

[vvvv]

http://www.woodheat.org/chimneys/wind.htm