Negative pressure smoke issue

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Slate Dale

Member
Dec 27, 2021
161
Slatington, Pennsylvania
Moved to a new thread.

Years ago, the Blaze King people coached my incompetent dealer on taking those draw readings. Supposedly it came up as good enough. Not great but in a range considered acceptable for the Ashford. It works as long as the seal is 100% perfect. Except maybe when the weather is warmer and the wind starts to blow. Running exhaust fans at those times is not a good idea, as it tends to draw negative pressure into the home, as well sealed as modern homes are.
I'm having a severe negative pressure problem with my new Blaze King 40 today, for the very first time. I've never seen anything like this happen with any stove or fireplace, in my experience. Smoke is pouring out of the bottom of the thermostat assembly box on the back of the stove and at the top where the thermostat control rod goes into the box (!!!) as well as from some of the seams in the black stove pipe and the collar, which I had sealed well enough (I thought) with stove cement.

When I say this happening, I closed the thermostat completely, which should, theoretically, have cut off the air supply and put out the fire, but it doesn't do that. So the fire is still smoldering, getting enough oxygen from somewhere. The stove is practically brand new, and the door gasket is still very tight. The ash removal door in the bottom has never been opened.

I had tested the venting for negative pressure for several days before installing this stove. Sometimes there was no n.p., other times weak n.p. that was easily reversible using a hair dryer for half a minute, and it usually stayed moving in the right direction (up) for a while afterwards. When starting fires, even when I used only a little kindling, there has always been good draft, and I never had to use a hair dryer or torch to get a fire started and no smoke ever back drafted out the door before.

Today the weather is very different than when I normally burn. It's in the fifties today instead of thirties and below. Today for the first time smoke pours out the door when I open it, and it is coming out of all the other places I mentioned before. I put a heat lamp on the stove pipe where it goes into the wall thinking that might encourage some upward air movement. I also opened the stove amidst the smoke and aimed a hairdryer up the vent thinking that would get it started. It seemed to do that for a few minutes.

The stove has become warm after more than an hour of smoldering, which should be enough to reverse any weak negative pressure. But it hasn't. Another puzzle to solve with this stove! I doubt there could be a clog in the venting since I have only burned about one fifth of a cord of wood in this new stove, most of it tested adequately dry. The 8 inch rigid stainless pipe, insulated with vermiculite cement, was installed less than three months ago, and it has a cap and screen so no animals could have gotten in.

This BK seems to be very finicky.
 
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stoveliker

Minister of Fire
Nov 17, 2019
6,354
Long Island NY
Yes, warm weather will negatively affect draft because draft is a function of the temperature difference between stove room and outside.

But, I'd stop burning and check your flue system. A blockage will do this too. And it's therefore dangerous, for CO reasons and chimney fire reasons if indeed a blockage is present.
 

Slate Dale

Member
Dec 27, 2021
161
Slatington, Pennsylvania
Yes, warm weather will negatively affect draft because draft is a function of the temperature difference between stove room and outside.

But, I'd stop burning and check your flue system. A blockage will do this too. And it's therefore dangerous, for CO reasons and chimney fire reasons if indeed a blockage is present.
That's what I plan to do. When I have a chance I will disassemble the stove pipe and look up and down see if there is a restriction. It would have to be an almost complete blockage, or very strong negative pressure I never had before, or maybe a combination of blockage and n.p. Meanwhile no more burning!

I have a CO alarm set up about twenty feet from the stove and it hasn't gone off yet but it sure is smokey.

I checked the stove again just now and it's almost out, kindling still smoldering a few places. I'm surprised there is no way to cut off the air supply to this stove. Closing the thermostat control (turning it all the way to the bottom) apparently doesn't do it.

I ran the stove for about three days straight the last time, about two weeks ago, and it seemed to burn nice and clean going at full blast, the window was clean, and the basement was hot.

I'm sharing this experience on this thread because it seems relevant. I hope the information is helpful.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,354
Long Island NY
You can't close off the air completely; there is a hole in the flapper that is run by the Tstat. This is to ensure a minimum burn rate, compatible with the cat. To keep things clean.

But when one wants to stop a fire, it's a pain, I agree.
 

Slate Dale

Member
Dec 27, 2021
161
Slatington, Pennsylvania
You can't close off the air completely; there is a hole in the flapper that is run by the Tstat. This is to ensure a minimum burn rate, compatible with the cat. To keep things clean.

But when one wants to stop a fire, it's a pain, I agree.
That's good information. I even tried stuffing material under the thermostat assembly box thinking that would help choke off the air. It would be helpful to have complete diagrams with explanations of every part of the stove.

I didn't want to spray water into the stove (which would cause corrosion) or waste a fire extinguisher.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
30,344
central pa
That's what I plan to do. When I have a chance I will disassemble the stove pipe and look up and down see if there is a restriction. It would have to be an almost complete blockage, or very strong negative pressure I never had before, or maybe a combination of blockage and n.p. Meanwhile no more burning!

I have a CO alarm set up about twenty feet from the stove and it hasn't gone off yet but it sure is smokey.

I checked the stove again just now and it's almost out, kindling still smoldering a few places. I'm surprised there is no way to cut off the air supply to this stove. Closing the thermostat control (turning it all the way to the bottom) apparently doesn't do it.

I ran the stove for about three days straight the last time, about two weeks ago, and it seemed to burn nice and clean going at full blast, the window was clean, and the basement was hot.

I'm sharing this experience on this thread because it seems relevant. I hope the information is helpful.
No modern stove allows you to cut off all of the air. And many classic stoves didn't either honestly
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
30,344
central pa
That's good information. I even tried stuffing material under the thermostat assembly box thinking that would help choke off the air. It would be helpful to have complete diagrams with explanations of every part of the stove.

I didn't want to spray water into the stove (which would cause corrosion) or waste a fire extinguisher.
Spraying water on it would probably destroy the cat. And can cause damage from the expansion as well.
 
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Slate Dale

Member
Dec 27, 2021
161
Slatington, Pennsylvania
That's good information. I even tried stuffing material under the thermostat assembly box thinking that would help choke off the air. It would be helpful to have complete diagrams with explanations of every part of the stove.

I didn't want to spray water into the stove (which would cause corrosion) or waste a fire extinguisher.
When an outside air supply assembly is added to a BK stove, does that make it possible to cut off the air to put out a fire? (I realize this is getting tangential to the thread topic.)
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
30,344
central pa
When an outside air supply assembly is added to a BK stove, does that make it possible to cut off the air to put out a fire? (I realize this is getting tangential to the thread topic.)
No
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
30,344
central pa
My old greenhouse stove, a rugged old classic stove, can be cut off completely.

I've never had a creosote problem with it either, and it burns everything to ash.
Some can yes. Any stove should burn everything to ash if you are using good dry wood. And yes old stoves if burnt hot enough could be didn't without creosote buildup.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,354
Long Island NY
What is the procedure to stop a fire?

See bholler. Shouldn't be necessary.

But, shovel sand in the firebox would be a good approach if a wrong needs to be righted by extinguishing the fire.
 

Parallax

Minister of Fire
Dec 2, 2013
873
Bellingham, WA
I don't know if it's true of all catalytic stoves or if Blaze King's are more prone to have this problem, but smoke leakage was really bad when I first got my Ashford. Struggled with it for a long time before a chimney sweep found a way to get the stove to work reasonably well. By which I mean, to end the constant leakage we were having our entire first year with the stove. Even after the fix, was so easy to get smoke in the house on reloads. Maybe we weren't set up ideally for this kind of stove. Perhaps it works fine for others with more draft or for those in colder climates where there's more of a temperature differential between inside and out. But I'm so glad to be moving on from catalytic technology. Way too fickle.
 

Slate Dale

Member
Dec 27, 2021
161
Slatington, Pennsylvania
Shoveling sand might have put this small load out, but it wouldn't work to stop a LARGE, full, load that suddenly begins pouring smoke out of the air intake and thermostat assembly at the bottom and back of the stove. I usually load it full to start.

Fortunately this time I started with only a few dry splits and some dry kindling.

Fortunately I had an open concrete basement floor to place some of the smoldering pieces, and douse them with water before carrying them outside. Fortunately I was at home when this happened or the house would be completely saturated with smoke, but it smells bad enough now.

I have lit new fires of all sizes in this stove many times before and never had ANY downdraft problems, not even any smoke escaping at the door when I threw in some extra kindling. This smoke-out is totally new.

This morning I disassembled the stove pipes and established that there is no blockage, just some soot in the pipes. The stove vent is working fine, no obstruction there either. The stove window is a little sooty from yesterday's smoke-out, but not glazed with creosote, and you can still see through all of it.

I had tested for negative pressure for several days before installing the stove. The only difference now is that the outdoor temperature is a little higher than when I tested, about fifty degrees now. No windows and doors were open upstairs when this happened. After it happened I opened lots of windows and doors.

This is a very smoke-prone stove. It should have been designed with a fail-safe mechanism to cut off the air supply. I will never cold-start this stove again without forcing the air up the venting with a hair dryer or torch until I am sure there is a sustained upward flow. I'm not sure I will even use this stove again, except in an emergency. I need to think long and hard about what to do with it. The dealer told me (afterwards) that "nobody buys those stoves," actually only one other person did besides me.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,354
Long Island NY
I don't think this is a stove issue. This is not common (it would be if it was a stove issue). Your venting system has been marginal ever from the start. Increasing outside temperature decreases draft - evidently past the threshold of what is needed for a cold start.

It's your flue stack.
 
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Slate Dale

Member
Dec 27, 2021
161
Slatington, Pennsylvania
I don't know if it's true of all catalytic stoves or if Blaze King's are more prone to have this problem, but smoke leakage was really bad when I first got my Ashford. Struggled with it for a long time before a chimney sweep found a way to get the stove to work reasonably well. By which I mean, to end the constant leakage we were having our entire first year with the stove. Even after the fix, was so easy to get smoke in the house on reloads. Maybe we weren't set up ideally for this kind of stove. Perhaps it works fine for others with more draft or for those in colder climates where there's more of a temperature differential between inside and out. But I'm so glad to be moving on from catalytic technology. Way too fickle.
The way this stove is designed, it doesn't seem to need much air and can draw enough air from the chimney, and pour its exhaust out of the thermostat assembly at the back and bottom of the stove, and there is no way to cut off the air supply to stop it. Is that where most of your smoke came from?
 

Slate Dale

Member
Dec 27, 2021
161
Slatington, Pennsylvania
I don't think this is a stove issue. This is not common (it would be if it was a stove issue). Your venting system has been marginal ever from the start. Increasing outside temperature decreases draft - evidently past the threshold of what is needed for a cold start.

It's your flue stack.
But this is a totally new surprise. There should have been some instance before of this back-drafting, but there wasn't. Most of my tests for negative pressure before installation were negative, and sometimes there was a slight downdraft easily reversible with a hair dryer and it seemed to stay reversed.

The vertical length of venting meets the manufacturer's specifications, including extra length for taking into account one 90 degree angle, one 45 degree angle and less than one foot of horizontal run between the angles. The only difference is a little higher outdoor temperature than usual, fifties instead of thirties.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
30,344
central pa
The way this stove is designed, it doesn't seem to need much air and can draw enough air from the chimney, and pour its exhaust out of the thermostat assembly at the back and bottom of the stove, and there is no way to cut off the air supply to stop it. Is that where most of your smoke came from?
And stove will be probe to doing that when starting a fire when it is upper 50s outside. If you shut off the air intake the smoke would just leak out elsewhere. Or be trapped until it reaches the ignition point then explode. Then it would have lots of places to leak out
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
30,344
central pa
But this is a totally new surprise. There should have been some instance before of this back-drafting, but there wasn't. Most of my tests for negative pressure before installation were negative, and sometimes there was a slight downdraft easily reversible with a hair dryer and it seemed to stay reversed.

The vertical length of venting meets the manufacturer's specifications, including extra length for taking into account one 90 degree angle, one 45 degree angle and less than one foot of horizontal run between the angles. The only difference is a little higher outdoor temperature than usual, fifties instead of thirties.

Negative pressure and a reverse draft due to temperature differential are different things. Negative pressure isn't fixed with a hair dryer
 
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Slate Dale

Member
Dec 27, 2021
161
Slatington, Pennsylvania
And stove will be probe to doing that when starting a fire when it is upper 50s outside. If you shut off the air intake the smoke would just leak out elsewhere. Or be trapped until it reaches the ignition point then explode. Then it would have lots of places to leak out

If I could shut off the air supply, since there is no blockage in the venting, if it was under so much pressure it would finally have the strength to go up the chimney where it is supposed to go.

When I disassembled the pipes this morning to look for a blockage, I did detect some negative pressure, but it is very mild, just like I had found before.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
30,344
central pa
If I could shut off the air supply, since there is no blockage in the venting, if it was under so much pressure it would finally have the strength to go up the chimney where it is supposed to go.

When I disassembled the pipes this morning to look for a blockage, I did detect some negative pressure, but it is very mild, just like I had found before.
I have seen glass blown out more than once from severe back puffs.