Too much draft with bypass open sucking flames into the pipe.

[MattA311]

I had the fire burn down into the inactive range earlier today. Loaded the box up with splits and had active flames coming out of the top of the rain cap. Just had the chimney professionally cleaned on Saturday so no this absolutely was not a chimney fire, it was the result of too much air and draft drawing actual flames up the stack with the bypass open. When I turned the t-stat all the way down it stopped.

In the future when having a fire with the bypass open waiting for the cat to get up to temp, what should I do to keep this from happening? Only thing I can think of is to run the air intake/tstat halfway instead of wide open. Hopefully the pipe didn’t warp.

 

[moresnow]

Did your Pro disconnect the connector pipe and vacuum the chim residue out from the upper part of the stove? Above the bypass? After he swept?
Whats your overall length of pipe?

 

[DonTee]

I think the fact it happened right after the chimney cleaning actually makes it more likely a chimney fire.

Is this your first time using the stove? If not, did it do this before?

I’ve burned a few stoves wide open. The only one I had flames come out of the chimney had a 6’ tall chimney . And that was burning cardboard

 

[stoveliker]

I'd have closed the bypass; evidently the gases were hotter than 550-600 F, so routing them thru the cat would have immediately lit it off. Even if the slow temp gauge doesn't show it yet.

And yes, I do think you had a chimney fire. (Aka fire in the chimney).

Indeed: how tall is the flue?

 

[MattA311]

The flu is 15 feet total, the interior stove pipe was removed and pipe was inspected after the cleaning. There was no creasote in the pipe after cleaning.

 

[kborndale]

The flu is 15 feet total, the interior stove pipe was removed and pipe was inspected after the cleaning. There was no creasote in the pipe after cleaning.

The pipe had no creosote but the top of the stove probably did. Sounds like a chimney fire to me, but that should be burnt away now and you should be good to go.

 

[stoveliker]

I thought it was appropriate procedure to have the chimney inspected after a fire (i.e. after there were flames in there).
@bholler ?

 

[MattA311]

The pipe had no creosote but the top of the stove probably did. Sounds like a chimney fire to me, but that should be burnt away now and you should be good to go.

It wasn’t a chimney fire, i’m convinced there was too much draft and the air was too wide open with the bypass not closed. We closed the bypass and turned the air down and it stopped. I guess in the future when starting a new fire I’ll have to do it with the tstat only halfway open.

 

[kborndale]

I've never heard of flames coming out the top of the chimney without having a chimney fire. Maybe I'm wrong.

 

[stoveliker]

What was the outside temperature?
A 15 ft flue is the minimum for many stoves - so too much draft is rather unusual.

To me "fire in the chimney" == "a chimney fire", regardless of what (and where) the fuel was originating from.
The point is that the chimney got hot, because there was fire in it. Hence my suggestion of an inspection to check the integrity. You even mentioned a concern about warping pipes yourself in your first post.

This is why it was asked above whether the crud that fell down when the pipe was cleaned, was cleaned off of the baffle (that the bypass opens, I presume).

What stove was this? (I'm reasoning from my BK stove design, given mentions of "active range" and "bypass").

 

[MattA311]

What was the outside temperature?
A 15 ft flue is the minimum for many stoves - so too much draft is rather unusual.

To me "fire in the chimney" == "a chimney fire", regardless of what (and where) the fuel was originating from.
The point is that the chimney got hot, because there was fire in it. Hence my suggestion of an inspection to check the integrity. You even mentioned a concern about warping pipes yourself in your first post.

This is why it was asked above whether the crud that fell down when the pipe was cleaned, was cleaned off of the baffle (that the bypass opens, I presume).

What stove was this? (I'm reasoning from my BK stove design, given mentions of "active range" and "bypass").

I thought I made it clear that all the “crud” pushed down was cleaned and cleared and that creosote inside the chimney or back of the stove was not on fire. Once the dial was turned down and bypass closed the issue resolved.

Having an inspection isn’t a bad idea even though flames were only up the chimney for a short period of time.

 

[stoveliker]

okay. That was not clear to me (interior of pipe was inspected, but nothing about stuff on the baffle) - but okay.

Yes, closing the bypass is a good idea in this case, as the cat would be either already at temp (despite the slow gauge still saying it's not) or would be very soon afte rclosing the bypass.

Anyway, I think this is a first for many folks here hearing about flames out of the cap when the person who observed it says it's not a chimney fire.
I've seen no other cases described like this.

 

[MattA311]

okay. That was not clear to me (interior of pipe was inspected, but nothing about stuff on the baffle) - but okay.

Yes, closing the bypass is a good idea in this case, as the cat would be either already at temp (despite the slow gauge still saying it's not) or would be very soon afte rclosing the bypass.

Anyway, I think this is a first for many folks here hearing about flames out of the cap when the person who observed it says it's not a chimney fire.
I've seen no other cases described like this.

I did a search and found a few others referencing similar events

 

[MattA311]

okay. That was not clear to me (interior of pipe was inspected, but nothing about stuff on the baffle) - but okay.

Yes, closing the bypass is a good idea in this case, as the cat would be either already at temp (despite the slow gauge still saying it's not) or would be very soon afte rclosing the bypass.

Anyway, I think this is a first for many folks here hearing about flames out of the cap when the person who observed it says it's not a chimney fire.
I've seen no other cases described like this.

I think the bottom line here is it was an overfire with the bypass open. When I say a glow or flames at the rain cap you’re thinking of it being typical of a chimney fire with them shooting out 6 feet tall. It was nothing like that.

 

[bholler]

I did a search and found a few others referencing similar events

Are you saying the flames were just sucked through the bypass a bit into the pipe? Or were flames coming out the top of the pipe? If its the first that's absolutely normal. The second not normal at all

 

[stoveliker]

I think the bottom line here is it was an overfire with the bypass open. When I say a glow or flames at the rain cap you’re thinking of it being typical of a chimney fire with them shooting out 6 feet tall. It was nothing like that.

Chimney fires don't need 6ft flames there, mostly a ton of smoke, flaming flakes coming out, and some fire visible if it's burning at the top - from my understanding.

I understand the mechanism you're proposing; I've seen flames sucked into the open bypass in my case too. But not to the extent that I thought they were 15 ft up (I have a taller flue so can't provide observations in this case).

Why I'm puzzled is that a 15 ft flue (in 32 F weather) is not so drafty that you'd expect to see unusual things as you did. (Now at -32 F I could imagine the draft being so strong that things may happen that are outside expectations.)

Can you provide examples of your search results?

Not to doubt, just to understand.

 

[Ashful]

A 15 ft flue is the minimum for many stoves - so too much draft is rather unusual.

Agree with everything stoveliker and others already said, but I have to pick a nit on this particular point. One of my Ashford 30's has about 15 feet of pipe on it, and it does indeed draft too hard. I know this, because I have a manometer and key damper on my other Ashford 30, and am able to easily observe behavior vs. draft setting on that rig.

It may be unusual for 15 feet to draft too hard on most stoves, but I think it's more common on stoves with a bypass in the ceiling of the firebox, and a pipe positioned directly above that.

Yes, BK spec's 15 feet minimum, but even this minimal chimney can and will pull too hard on the stove when it gets hot, standing in bypass long enough to get the cat to active.

You'll learn that you do NOT need to wait for the cat probe to indicate active, to close the bypass and achieve light-off. Close that bypass as soon as you meet any combination of the following criteria:

1. Stove flue gas > 600F on flue probe ~ 18 inches above stove.
2. Single wall stove pipe exterior temp > 300F on stove pipe thermometer ~18" above stove.
3. Wood load completely charred over, or burning vigorously.

I would bet it's been 6-7 years since I've (intentionally) waited for the cat probe to actually reach Active threshold before closing the bypass on my stove running 15 feet of pipe. It's totally unnecessary, and hard on your bypass and stovepipe components to do this. BK includes that instruction in their manual as a "sure fire" way to achieve light-off and prevent a stall, for new and novice users, but your experience will quickly push you beyond religious adherence to that rule. Most of the time, my cat starts glowing within 10 seconds of closing the bypass, even though the probe indicates I'm still down in the middle of the "Inactive" region.

 

[DonTee]

Also the “drafting too hard” would be a setup issue and not a stove issue. BK has a draft spec and it should be checked when the stove is installed. If it’s not, the stove can run outside of its intended parameters

You might need a key damper like Ashful. But I wouldn’t put one in until you check the draft with a manometer

I bet if you loaded the stove up with really dry wood (like 2x4 cutoffs) and really let it rip with the bypass open, you might get flames out of the chimney cap. But the flue temp would really be up there.

Having a flue temp probe to see what’s going on in there is very helpful. For me, just looking at the fire, I can’t tell the difference between 500 degrees and 1000 degrees flue temp with the bypass open. And it climbs quickly once it hits about 700.

 

[Wisco Shepherd]

That would be a hell of a fire to be coming out of the cap without something in the chimney being lit. I've made flames 15 feet high before but that's usually when burring a brush pile the size of a minivan.

 

[DonTee]

I just think about burning stuff outside in my short chimney woodstove. Once it gets so hot there isn’t complete combustion inside the stove. Gases go up the chimney and ignite at the top.

Like this. That flame is 3’ tall for reference.

 

[shoot-straight]

Inhave 27' of pipe on my ashford and it can suck like a wind tunnel if you are not careful. My turn (key) damper is the key when that happens.

I think chimney light offs can happen more readily in blaze king's because when bypass is open, it's a straight shot up the pipe. East for a piece of paper or whatever to get sucked up.

 

[Wisco Shepherd]

Agree with everything stoveliker and others already said, but I have to pick a nit on this particular point. One of my Ashford 30's has about 15 feet of pipe on it, and it does indeed draft too hard. I know this, because I have a manometer and key damper on my other Ashford 30, and am able to easily observe behavior vs. draft setting on that rig.

It may be unusual for 15 feet to draft too hard on most stoves, but I think it's more common on stoves with a bypass in the ceiling of the firebox, and a pipe positioned directly above that.

Yes, BK spec's 15 feet minimum, but even this minimal chimney can and will pull too hard on the stove when it gets hot, standing in bypass long enough to get the cat to active.

You'll learn that you do NOT need to wait for the cat probe to indicate active, to close the bypass and achieve light-off. Close that bypass as soon as you meet any combination of the following criteria:

1. Stove flue gas > 600F on flue probe ~ 18 inches above stove.
2. Single wall stove pipe exterior temp > 300F on stove pipe thermometer ~18" above stove.
3. Wood load completely charred over, or burning vigorously.

I would bet it's been 6-7 years since I've (intentionally) waited for the cat probe to actually reach Active threshold before closing the bypass on my stove running 15 feet of pipe. It's totally unnecessary, and hard on your bypass and stovepipe components to do this. BK includes that instruction in their manual as a "sure fire" way to achieve light-off and prevent a stall, for new and novice users, but your experience will quickly push you beyond religious adherence to that rule. Most of the time, my cat starts glowing within 10 seconds of closing the bypass, even though the probe indicates I'm still down in the middle of the "Inactive" region.

Interesting thought on operation. I have previously thought about turning air down to limit an over enthusiastic fire while waiting for my cat probe to reach the active zone but maybe if it's been 10 minutes and things are rocking and rolling I should just engage the cat. I'm sure my bypass damper would appreciate it as would the first couple feet of stove pipe coming out of my stove.

Sorry to hijack thread, but no real sign of OP lately.

 

[Tron]

but maybe if it's been 10 minutes and things are rocking and rolling I should just engage the cat.

That's what I do, too, but mostly go by flue temperatures. I even engage the cat and turn down the thermostat.
And five minutes later the cat gauge caught up and shows active...

 

[DonTee]

Sometimes if the flue temp is getting too high I’ll turn down the temp gauge until the cat gets close to the active range. It seems to happen more on cold starts. On hot reloads the cat is already very close to the active zone.

I still char the wood with the bypass open on hot reloads. I figure it’s less cold wood smoke to push through the cat.

 

[Ashful]

Interesting thought on operation.

I decided to grab pics for you with this afternoon's load, engaging extra early to prove a point. The cat still went straight to glowing, within maybe 20 seconds of closing the bypass, indicating it was probably over 1000F, and way beyond active.

This stove has a probe thermometer in double-wall pipe, so temperature is about double what you'd see on outside of single wall pipe steady-state, or even more discrepancy during heat-up phase.



This is honestly pushing "early", even for me, as I'd normally wait for the flue probe to be more like 500 - 600. But even down at 400F on the flue probe, the cat still managed to take off, thanks to a vigorous fire and very dry wood. For you, I'd recommend doing it at probe = 600F or external single wall = 300F, as a more surefire way of going quickly into light-off.

I thought I had a photo of the fire as well, but I guess it didn't take. Next time!