small chimney fire ?

I had a weird experience yesterday evening. The stove had been smoldering since the night before, with the catalyst temp in the active zone most of the time. The house getting cold again and evening coming, I re-loaded and let the thing rip for awhile, due to distraction, probably a bit longer than I needed to to get the cat active again.

I started hearing a kind of "crinkly" sound coming from the connector pipe - almost sounding like there were particles falling. I didn't think too much of it, until I hit the connector pipe with the IR thermometer, and got about a 600 degree reading. Yikes ! It's single wall, but still, I think that's too high. After I engaged the cat though, it quickly fell to the typical 200-300 degrees or so.

I wonder how worried I should be. This has actually happened in the past, I'm now recalling, but before I had an IR thermometer or bothered checking. Typically my chimney is very clean, as I'll go 2-3 years without cleaning it, and then when I do, get perhaps 2 quarts in volume of dry flaky black stuff. And most of that is in the connector pipe. So I'm thinking some creosote builds up in the connector when I slow burn for a long time, and then when I let her rip to get a new fire going, that creosote lights off.

Maybe the worn out gasket on the bypass plate, which I never worried much about, is letting too much creosote into the chimney even when the cat is active ? Maybe I just need to be less "enthusiastic" when reloading after a long slow burn.

bholler said:

Sounds like it could have been a small fire or just stuff falling off the pipe ...

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With 600 degrees temp on the outer wall of the single-waqlled connector, I have to think something a little odd. I only measure 300 when I've got a VERY hot fire and the cat active.

... when in doubt pull it apart and check everything out.

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Not sure what I'd be looking for exactly. Since the connector is single-wall, if it was starting to melt through or anything like that, seems like it'd be just as obvious from the outside. I guess I should remove the connector and/or the chimney cap and look down there with a powerful flashlite, though again, not sure exactly what I'd be looking for.

BobUrban said:

Doesn't sound like a fire as much as it sounds like a hard rush of hat air and some crud falling off. No bad reason to inspect, ever, after a concern but this does not sound like a chimney fire from what you described.

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Yeah, it definitely sounded like crud falling off. Like I said, from cleaning my chimney (every 2 years at most) there just ain't that much crud in there, but most of what is, is in the connector pipe. I guess I should try to conspire to have a long smoldering burn before the next time I clean the chimney.

Do you have snow? Popcorn looking creo will typically be evident down wind if you had a fire in there along with other black crud.

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No snow, but "mill finish" (shiny aluminum-color) metal roof, so I'll go see if anything looks weird up there.

begreen said:

Is the connector straight up to the chimney or does it have a turn in it?

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It comes straight up from the stove for 2 ft, then a 30-degree elbow, then 1ft straight, then another 30-degree elbow to go vertical again, then about 1.5ft to the metal chimney. Never had much problem with draft - maybe if I jerk the door open during a smoldering fire, some smoke will spill out.

begreen said:

Sote may be accumulating in the diagonal section. That's where the most rapid cooling of the pipe will be.

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Yeah, sounds likely, although at cleaning time, I don't think the soot is that much more in the bends.

The good news is, this only seems to be a problem when I'm letting her rip on a reload (or new fire), with the bypass open, after a slow burn - so I'm going to be paying attention. And also, I'll not let her rip quite so much !

Well, tonite I reloaded after a long smolder and let her rip. No funny sounds from chimney or any other bad signs, but connector pipe was still 600 degrees or so. So I guess that's not all that unusual (I would appreciate readings from other BK owners with single-wall connector). I'm less worried.

Bump, alluding to my previous post ... Could any folks with single-walled connector pipes, especially those with BK or other catalytic stoves, and an IR gun, report what temperature they typically see just before closing the bypass ? Thanks.

fox9988 said:

I think we are much better off avoiding a chimney fire by keeping the chimney clean vs by keeping the pipe temp down. Can't have a chimney fire with no fuel (creosote) in the chimney.

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Sure, but my chimney tends to be very clean; I'll go 2-3 years between cleaning and not get much crap (maybe a quart or so, in volume, of flakey black stuff). And as far as the episode I was disturbed about in my OP, we're talking maybe 1/2 a burning season between the last cleaning (Oct '14) and the episode.

Thanks for the input about your pipe temperatures.

fox9988 said:

I think the crinkling is from the heat expanding the pipe, causing bits of soot to fall off.

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I think you nailed it. Thanks.