I've got a 1976 Comforter from the stove works in Lochmere, NH. In the past I was always able to regulate a steady burn with 7 inch smoke pipe going into a fireplace smoke chamber to a 12 inch x 12 inch clay flue. Now I've got a 6 inch insulated, stainless steel flue liner inside my 12 x 12 clay flue. I installed it after learning that it would be much safer and after having to put up with too much liquid creosote dripping down the walls of the fireplace. This setup has caused my seasoned hardwood fire to "runaway" several times since the beginning of the 09 heating season. Three sticks of smoldering wood sometimes begin to burn violently and when my wife and I panic and shut the air feed all the way down the fire begins to gulp air down the chimney and the resulting mini-explosions actually lift the kettle lid and a nasty flame blows out! I have talked to several people in the business about this, because I am very concerned. One fellow says that a barometric damper will not fix the problem. He says what I need is an electric "paddle wheel" called a draft inducer. Another guy at the stove shop says that my Comforter stove is probably no longer air tight; says all the seams need to be re-sealed (although it looks pretty air tight to me). He says that I should install a 6 inch cast iron damper inside my exit pipe to regulate my chiminey draft. Can somebody with real experience advise me about this awful problem?
"Whuffing" takes all the joy and relaxation away from using your wood stove
- Thread starter rennman
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cmonSTART
Minister of Fire
Not having seen the situation personally, my first gut reaction is to agree with the stove not being air tight anymore and installing a keyway damper to help regulate things.
I didn't have the woofing but the overdraft and lack of control happened with my old slammer insert when I installed a liner. It turned into the blast furnace from hell. But that was because in addition to the fantastic draft I also found a cracked weld that was letting too much air in. I junked the stove, which had paid for itself many years ago, and replaced it.
A key damper in the pipe would be a good thing to see if it gets it back under control.
A key damper in the pipe would be a good thing to see if it gets it back under control.
Backwoods Savage
Minister of Fire
I'm not sure about the air leaks because he can shut the draft down and then the smoke just sits there.
You state when you shut the air down all the way you get the smoke. Well, that fire needs draft to keep the smoke going up the chimney so if you cut the draft off, what will happen to the smoke? Simply put, don't shut the draft completely.
You state when you shut the air down all the way you get the smoke. Well, that fire needs draft to keep the smoke going up the chimney so if you cut the draft off, what will happen to the smoke? Simply put, don't shut the draft completely.
Hi Inferno,
Appreciate your input. No. No excessive smoke when we shut the air inlet all the way; just a raging out of control fire that could raise the flue temp to over 800. Scary! Do you think that this has something to do with the new setup... 16 feet of 6 inch flue liner sucking on the Comforter firebox? Because this kind of thing never happened at two different locations when a short 7 inch pipe went directly into a fireplace smoke chamber. Where is the fire getting its air from? I examined the cast iron box; the seams are factory sealed on the outside with furnace cement (one vertical seam on the left front re-done by me last season). I find it hard to believe that tiny cracks could be casing this especially since it did not happen when this very same stove was piped right into the fireplace smoke chamber. This must have something to do with the new flue liner. Maybe the 6 inch keyed cast iron damper disc will solve it, I don't know.
Appreciate your input. No. No excessive smoke when we shut the air inlet all the way; just a raging out of control fire that could raise the flue temp to over 800. Scary! Do you think that this has something to do with the new setup... 16 feet of 6 inch flue liner sucking on the Comforter firebox? Because this kind of thing never happened at two different locations when a short 7 inch pipe went directly into a fireplace smoke chamber. Where is the fire getting its air from? I examined the cast iron box; the seams are factory sealed on the outside with furnace cement (one vertical seam on the left front re-done by me last season). I find it hard to believe that tiny cracks could be casing this especially since it did not happen when this very same stove was piped right into the fireplace smoke chamber. This must have something to do with the new flue liner. Maybe the 6 inch keyed cast iron damper disc will solve it, I don't know.
You say you had a 7" pipe going directly into a fireplace smoke chamber and then into a 12x12 flue, correct? Did you need to reduce to 7" to get past the fireplace damper or is the stove collar itself 7"? Reason I ask is many stoves from that time period had an 8" collar and called for 8" pipe. If so, you have already restricted the capacity by almost half, the last thing you'll want to do is add a pipe damper to restrict if further.
Sounds like the stove isn't get enough air (smoldering splits) until the flue gets hot enough to create a strong draft, then the thing takes right off. You then get alarmed and shut the intake air down, but the smoke builds up and ignites as a small explosion when air from the chimney hits the hot gasses.
Start with smaller fires until you get a good draft established, then experiment with progressively larger loads that are not big enough to cause an overfire. That way you can avoid shutting the air down too far on a hot fire, a sure way to induce the severe backpuffing you are experiencing.
Sounds like the stove isn't get enough air (smoldering splits) until the flue gets hot enough to create a strong draft, then the thing takes right off. You then get alarmed and shut the intake air down, but the smoke builds up and ignites as a small explosion when air from the chimney hits the hot gasses.
Start with smaller fires until you get a good draft established, then experiment with progressively larger loads that are not big enough to cause an overfire. That way you can avoid shutting the air down too far on a hot fire, a sure way to induce the severe backpuffing you are experiencing.
Stump_Branch
Minister of Fire
Hi Pyro and Fire Honor,
The smoke exit port on my old Comforter is 7 inch but it is oval. That makes it less than 6 high and a bit more than 9 wide. Never the less, squeeze a 7 inch pipe into an oval shape and it fits in tightly. The area of the oval might be the same as the area of a 6 inch round pipe... I don't know. But all of you guys have great input from your experience and I really appreciate it. Looks like my problem does have something to do with changing over to a 6 inch flue liner. I need either a 7 inch flue liner or a new stove with a 6 inch exit port in the rear.
The smoke exit port on my old Comforter is 7 inch but it is oval. That makes it less than 6 high and a bit more than 9 wide. Never the less, squeeze a 7 inch pipe into an oval shape and it fits in tightly. The area of the oval might be the same as the area of a 6 inch round pipe... I don't know. But all of you guys have great input from your experience and I really appreciate it. Looks like my problem does have something to do with changing over to a 6 inch flue liner. I need either a 7 inch flue liner or a new stove with a 6 inch exit port in the rear.
One other thing... I just remembered. The couple of times I set up this stove with 7 inch smoke pipe going directly into the smoke chamber... yes the 7 inch had to be squeezed into an oval shape to go through the angled cast iron damper. That's another reason I bought a 6 inch liner... it goes straight up from a stainless tee, but I still had to cut clearance notches into the cast iron damper frame. I suppose the 12 x 12 clay flue could have taken a 7 incher, but the damper frame was the limiting factor.
Stump_Branch
Minister of Fire
rennman said:
Rennman, the names you use are the 'title' of sort due to the amount of posts (otherwise I know you as firestarter!)
I'll agree, your oval is 42.41in^2. a 6in. is 28.27in^2 and 7in. is 38.48in^2. so upsizeing to 7 will be better then the 6. (8" is 50.27in^2)
of course the new stove is always a nice option as well, new epa.....tis christmas season, ask santa...
I think the discussions about what size pipe and connection is masking what is an operating issue.
"whuffing" is going to happen anytime an airtight stove has its air choked off. Its caused by the stove generating more flamable gas from the wood than there is air to burn it. With the prior setup, the draft was lousy and most of the flamable gases would travel into the fireplace where it condensed into "liquid creosote dripping down the walls". When the flue was direct connected, you got rid of a place for the gases to subcool and at some point along the stack enough oxygen gets down the stack to allow ignition back to the stove. Direct connecting the stove also most likely doubled the heat output as its directly related to the stove draft which was probably real low with the old set up. Speculation on my part is that your burn routine is to get the fire going then fill up the firebox with big splits and use the air damper to control the stove output to maximize how long between reloadings? This creates a lot of thermal mass in the firebox which leads to a lot of wood gas generation which is mostly independent of the amount of air in the firebox. What you need to do is cut down on the fuel generation rather than trying to cut back on air.
So now you have a stove that puts out a lot more heat due to much better draft and no longer has a big relative cold secondary chamber (the fireplace) to condense out a lot of the flamables. The solution is to control the stove the way it should be. Burn smaller loads of wood and feed the stove more often to control the heat output, regard the air damper as a secondary control to possibly trim the output a bit but it rarely should ever close. One of the fundamental ways of making a stove an EPA stove is to make it so the damper cant close. This makes it so that as long as the stove is producing gas, it will burn. Unfortunately if the wood stove is an a living space, it makes it hard to have a long slow burn.
This is going to take some relearning as the "whuffing" is going to be more noticable in the shoulder seasons, spring and fall. Since the stove has a higher output now, you will probably end up using a lot less wood, but I will admit that the frequent stove feeding is more of a PITA.
By the way, I have a VC defiant hooked to a 35' inside masonary stack, it took about a couple of years of relearning how to burn after switching from a fisher (which didnt have an air damper). I am lucky in that the stove is a basement so I can let it run full bore if need be, but if I was not paying attention in the evening and overfilled it before going to bed without opening up the damper, I would get the whuff. The VC even has a secondary air port installed on it to help to keep it from being starved from air but even with that open I can get a whuff by throwing in a pile of wood in a hot firebox and then cranking down the main damper
Sticking a damper in the pipe will drop the stove output somewhat but really wont directly solve the fundamental problem. It may help, but changing the way you burn will cure it. If you buy a new EPA stove, you are going to be forced to relearn how to burn it so why not save the "tuition" from buying a new stove and apply the same concepts to your existing stove?
Good luck
"whuffing" is going to happen anytime an airtight stove has its air choked off. Its caused by the stove generating more flamable gas from the wood than there is air to burn it. With the prior setup, the draft was lousy and most of the flamable gases would travel into the fireplace where it condensed into "liquid creosote dripping down the walls". When the flue was direct connected, you got rid of a place for the gases to subcool and at some point along the stack enough oxygen gets down the stack to allow ignition back to the stove. Direct connecting the stove also most likely doubled the heat output as its directly related to the stove draft which was probably real low with the old set up. Speculation on my part is that your burn routine is to get the fire going then fill up the firebox with big splits and use the air damper to control the stove output to maximize how long between reloadings? This creates a lot of thermal mass in the firebox which leads to a lot of wood gas generation which is mostly independent of the amount of air in the firebox. What you need to do is cut down on the fuel generation rather than trying to cut back on air.
So now you have a stove that puts out a lot more heat due to much better draft and no longer has a big relative cold secondary chamber (the fireplace) to condense out a lot of the flamables. The solution is to control the stove the way it should be. Burn smaller loads of wood and feed the stove more often to control the heat output, regard the air damper as a secondary control to possibly trim the output a bit but it rarely should ever close. One of the fundamental ways of making a stove an EPA stove is to make it so the damper cant close. This makes it so that as long as the stove is producing gas, it will burn. Unfortunately if the wood stove is an a living space, it makes it hard to have a long slow burn.
This is going to take some relearning as the "whuffing" is going to be more noticable in the shoulder seasons, spring and fall. Since the stove has a higher output now, you will probably end up using a lot less wood, but I will admit that the frequent stove feeding is more of a PITA.
By the way, I have a VC defiant hooked to a 35' inside masonary stack, it took about a couple of years of relearning how to burn after switching from a fisher (which didnt have an air damper). I am lucky in that the stove is a basement so I can let it run full bore if need be, but if I was not paying attention in the evening and overfilled it before going to bed without opening up the damper, I would get the whuff. The VC even has a secondary air port installed on it to help to keep it from being starved from air but even with that open I can get a whuff by throwing in a pile of wood in a hot firebox and then cranking down the main damper
Sticking a damper in the pipe will drop the stove output somewhat but really wont directly solve the fundamental problem. It may help, but changing the way you burn will cure it. If you buy a new EPA stove, you are going to be forced to relearn how to burn it so why not save the "tuition" from buying a new stove and apply the same concepts to your existing stove?
Good luck
Dear peakbagger,
I thank you in depth for your asessment. You are obviously "right on" because my wife and I have been finding our way to this method of using the Comforter already. It hasn't "whuffed" in all this time and Thank God for the wonderful thermocouple thermometer I bought from Thermoworks. The tip of the sensor wire is fastened to the top of the horizontal flue exit behind the stove. I have the alarm set for 300 degrees. It chirps to let us know that it's time to start regulation of the air feed. Thanks very much for all your help and best regards to your great state of New Hampshire.
I thank you in depth for your asessment. You are obviously "right on" because my wife and I have been finding our way to this method of using the Comforter already. It hasn't "whuffed" in all this time and Thank God for the wonderful thermocouple thermometer I bought from Thermoworks. The tip of the sensor wire is fastened to the top of the horizontal flue exit behind the stove. I have the alarm set for 300 degrees. It chirps to let us know that it's time to start regulation of the air feed. Thanks very much for all your help and best regards to your great state of New Hampshire.
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