Chimney fire after two weeks???

[Highbeam]

I think this is to be measured under steady-state condition, with the stove, thermostat and flue at whatever temperature they stabilize after sufficient time. Once set, I can run my stove thru a full load on high, and it doesn't typically drift at all. I certainly don't go thru any effort to try to time it before the stove heats up.

But you understand that during warm up the intake valve is open and then as the stove heats up the intake valve closes which causes the exact situation you warned against of testing the draft strength with a partially closed intake valve.

 

[brenndatomu]

The draft is what it is under any "normal" operating conditions (doors closed, bypass closed, etc) if there is an auto control on the stove that adjusts and makes the draft go out of manufacturers spec, then the draft is just plain not well controlled and it needs to be addressed, unless you are going to choose to ignore it.
That's why I like having a barometric damper on my wood furnace, doesn't matter what the furnace controls do, the draft stays wherever you have the BD set to.
I know all you stove guys think BD's are evil though...but I can tell you this, after using one for over 10 years now, they are highly effective, no matter what you think of them.

 

[Woodsman on the Plains]

Thank you @Ashful and @Highbeam for that discussion. And I shut the damper down when it was on high on a cold start right after I shut the bypass.
As for the stove. First day with key damper and dwyer installed so far so good! I will take a line from another thread and say "this thing is silly!" This is the first time I've come home from work after 10 hours and I still have half my load left cat probe still active and putting off decent heat. Granted it's not a ton of heat but I don't need a lot for the basement. I'm finding out where my "low" setting is for this particular set-up. This is how I expected the BK to work with all the hype about em! I honestly don't even think I'll mind if I have to clean the pipe more than the SBI ZC fireplace upstairs. If I only have to come down and mess with this thing once or twice a day that's what I was hoping for! I'll attach pics of how it's running after 10 hours

 

[Woodsman on the Plains]

Now I just need to figure out how to clean the pipe from the inside with the key damper installed, I wonder if i can sneak a soot eater in there...🤷

 

[brenndatomu]

Now I just need to figure out how to clean the pipe from the inside with the key damper installed, I wonder if i can sneak a soot eater in there...🤷

SE will go right past an open key damper no problem

 

[Highbeam]

SE will go right past an open key damper no problem

Open the key damper, remove the probe meter, and the sooteater scoots right on by.

 

[Ashful]

But you understand that during warm up the intake valve is open and then as the stove heats up the intake valve closes which causes the exact situation you warned against of testing the draft strength with a partially closed intake valve.

Yes, of course! As it was when BK came up with the number they printed in the manual. I don't think they played any special games to hold that thermostat open against its will, when determining ideal draft for the stove. Let the thermostat do its thing, you'll quickly see there's a near-steady state achieved after initial warm-up, that holds through most of the burn cycle. At the end of the burn cycle, as the stove cools and the thermostat starts to open more, yes... measured draft will decrease. But that's fine, as we're really only fighting over-draft with these key dampers, I'm never in any danger of under-draft on a warm pipe.

Open the key damper, remove the probe meter, and the sooteater scoots right on by.

Anyone else shoot the thing twice, flipping the damper in-between? I set my key damper open, and do the entire pipe. But on the way back down, I stop after betting back below the key damper, give the thing a flip, and shoot back up thru it (damper area only not full chimney) to knock the other side clean.

 

[stoveliker]

I think Ashful is hitting the nail on the head: in steady state full burn, the flapper does not "open" and "close" - it is (barring big changes in the firebox) dithering around some constant "level of open". It's not a thermostat like the one controlling my (unused) oil boiler that switches between 1 and 0. This "continuous range of output actions" is a nice thing about an analog technology that is the bimetal coil.

As a result, checking the draft with a full burn steady state, should give one a reliable number. (Until your fuel collapes/rearranges in the box and some larger changes in the flapper might be happening as a result.)

 

[Woodsman on the Plains]

So just out of curiosity I let er rip with key damper open...😬... .18-.19 kinda floating back and forth with 30 mph winds outside. Geeze no wonder I wasn't able to get a longer burn I was hoping for. (BTW I don't think the new manuals have the draft spec in them. At least I can't find it anywhere).
Anyway I bought a condar cat thermometer and if I'm not mistaken the BK is just a repurposed condar (please correct me if I'm wrong) that being said when I was first running the thing before my flue probe was installed I would regularly see the needle in the 6 o'clock position, that's like 2,000° or more on the condar...😵‍💫. What do you all think. Is it possible I damaged the cat?

 

[Ashful]

...6 o'clock position, that's like 2,000° or more on the condar...😵‍💫. What do you all think. Is it possible I damaged the cat?

Yes, it does look like the BK probe is a Condar that's been private labeled for them. But I don't know if the calibration/range is the same, such that you can actually translate the "o'clock" from one to the other. Someone (@Highbeam?) did a comparison many years ago, swapping them in the same stove, and found at that time theirs was a direct translation. But at least one or two others have repeated the test more recently, and found they did not see agreement between the BK original and a newer Condar.

In any case, at 2000F you're in the territory of starting to flatten out the wash coat. My interpretation of the descriptions I've received from those in the know, is that it starts out looking like a microscopic lawn of precious metals planted on the substrate, with all the grass blades sticking up. After extended time, it begins to look flattened out, like the lawn at the end of a slip-n-slide. Higher-temperature exposure (eg. 2000F) only accelerates the process, although it's unlikely one event for an hour or three did a whole lot of damage.

When you get even hotter than 2000F, the wash coat can actually peel off the substrate. Maybe someone remembers the threshold for that, although I do suspect all published numbers on that would be based on the Legacy coating, and that the newer V3 coating used by BK might have a different temperature threshold for peeling.

 

[stoveliker]

I think the V3 has more to do with the precious metals on the (oxide) wash coating than the wash coating itself.

But at high temps both will flatten out; the precious metals are on the coating in as small "pieces" as possible (often preferably single atoms, but more likely nanocrystals). (Precious) metals on oxides tend to ball up like that (rather than be a continuous film) due to easy diffusion of the precious metals.

The point in both coating (essentially a substrate termination layer to make the metals work properly) and metal (size) is to increase the surface area as much as possible, to get as much as possible interaction with the gases passing by. High temps tend to make the metal diffuse over the oxide surface faster, leading to larger balls of metals (hundreds of nanometers diameter), and thus a smaller number of exposed metal atoms. A lower surface area overall and a lower number of metal atoms exposed leads to a lower activity of the combustor.

Now, new cats are always hyper active due to ideal surface roughness and metal particle distribution.
The heat due to the hyperactivity will result in their fabrication-finish roughness and metal particle distribution changing. It is likely in my interpretation that this restructuring leads to the "showing more adult behavior" of the new cat after a while. The corollary is that then less heat is produced (because it's a bit less active), and less diffusion happens, and the rate of combustor changes will decrease.

Bottomline: I don't think the initial high temps *due to activity of the cat itself* (even if 2000, unless the washcoat delaminates off of the steel) are a problem; it'll settle into a normal active mode because the high temp won't be reachable after restructuring.

Now, consistent pushing of the temp of the cat by external forces (as in too high draft or so) *will* damage the cat, because it's being pushed to this temp. That (in my view) is different than it heating up "by itself", leading to changes, leading to lower capability of heating up again.

My 2 cts (I did (also) do surface catalysis research in a national lab, using atomic scale techniques and electron spectroscopy).

 

[Highbeam]

Pretty wild how out of spec your draft can be on a normal chimney. Makes me wonder if the prescribed 15’ chimney is out of spec too and the old recommendation of 12’ is closer for draft/performance but caused too many complaints of smoke roll out.

Overtemping the cat when it’s new is not supposed to be a problem on a properly installed stove but on an overdrafting stove it could be. It’s too late now, so just go with it.

Nobody with that knowledge has said that the factory bk meter is the same scale as the condar numbered meter. I’ve owned both and found the condar slower to wind up or in other words less likely to go to 6pm. The most important information is the active line. I suggest that you not flirt with barely keeping the meter above the active line but keep it well above. My stove, on low, burning softwoods, keeps that cat meter way up near 1000 for most of the very long burn.

 

[Ashful]

Pretty wild how out of spec your draft can be on a normal chimney. Makes me wonder if the prescribed 15’ chimney is out of spec too and the old recommendation of 12’ is closer for draft/performance but caused too many complaints of smoke roll out.

Judging by behavior alone, yes... 15 feet is already over-drafted. I've not proven it by putting a gauge on my shorter chimney, but the stove on that chimney behaves like classic over-draft. If I run it on high for any extended period, the cat probe pegs and the firebox is white-hot. Conversely, the stove wearing a damper and magnehelic on 30 feet of pipe runs much more tame.

 

[joop]

i'll stick with my tube burner ,sheesh

 

[Highbeam]

i'll stick with my tube burner ,sheesh

I have one of each. Definitely prefer a good cat stove in the house to keep it warm.

 

[Ashful]

I have one of each. Definitely prefer a good cat stove in the house to keep it warm.

Yeah, but you’re a competent and intelligent operator, which is more than we can say for some contributors to this thread.

 

[Highbeam]

Yeah, but you’re a competent and intelligent operator, which is more than we can say for some contributors to this thread.

I don’t know about all that but I feel like I have this cat stove pretty figured out.

 

[Ashful]

I'll personally never understand anyone who claims cat stoves are somehow uniquely complicated to run. If you find that to be the case, you have the wrong setup or the wrong stove. Each of my kids have been managing mine just fine, based on timers I set for them after I load it and head outside, since they were about 8 years old. I'm in the barn or out in the yard, in case they have any trouble and need something, but they never do. Unless you have wet wood or an improper installation, they're really quite simple and predictable.

 

[Highbeam]

Unless you have wet wood or an improper installation, they're really quite simple and predictable.

Yes, but much less simple than a noncat with a single air control and no timers.

 

[Ashful]

No timers??? This forum is quite full of posts of run-away non-cats, with the old hands here telling the user to try turning down several minutes sooner. If I had time to waste, I could find and quote probably 10,000 posts discussing the technique of turning down a non-cat in several increments, spaced 5 minutes apart. There must be a timer involved.

So I'm only speaking from what I've read, but it seems its quite the opposite, in that I can leave my stoves run full-bore all day and night, with no issue. I do use a timer, but only so that I don't forget to comee back and close the bypass damper at some point, it's timing is completely non-critical to operation.

 

[Wildflush]

No timers??? This forum is quite full of posts of run-away non-cats, with the old hands here telling the user to try turning down several minutes sooner. If I had time to waste, I could find and quote probably 10,000 posts discussing the technique of turning down a non-cat in several increments, spaced 5 minutes apart. There must be a timer involved.

So I'm only speaking from what I've read, but it seems its quite the opposite, in that I can leave my stoves run full-bore all day and night, with no issue. I do use a timer, but only so that I don't forget to comee back and close the bypass damper at some point, it's timing is completely non-critical to operation.

I don’t use a timer on my Vista. Just watch what the fire is doing and turn it down in increments. Easy. Early on when getting use to the stove I turned it down later than I should. No big deal since I closed the air and STT hovered around 650. Nowhere near an overfire. I normally like 550-625 STT. I don’t overload my stove with fuel so that also brings down the risk of overfire also.

 

[stoveliker]

The point is that that's about what I do too. Ashful uses a timer, but I look at (the temperature rather than the flames). Every stove needs to be turned down at the right time. Cat stoves are (thus) not more complicated - unless (upon a hot reload) closing not only the door but swinging another handle as well makes it rocket science....

 

[Ashful]

I should also note that I only use a timer when walking away from the stove. I have a habit of getting distracted or caught up in other things, and forgetting about the stove for an hour. Bad habit, if it's in bypass. The timer is a simple reminder to come back and close the bypass.

If I'm sitting in the room with the stove, I drive it by eye or by ear, depending on whether I'm looking at it from my sofa or at my desk with my back to the thing. That said, I did fall asleep on the sofa a few weeks ago with a full fresh load of oak, and the stove in bypass. No harm done, but my god... things got warm!

 

[Highbeam]

The point is that that's about what I do too. Ashful uses a timer, but I look at (the temperature rather than the flames). Every stove needs to be turned down at the right time. Cat stoves are (thus) not more complicated - unless (upon a hot reload) closing not only the door but swinging another handle as well makes it rocket science....

Yes, swinging a second lever when a particular set of instruments or parameters indicate it is time to do so is more complicated than not swinging a second lever. ALso don't forget that you need to feel the "click".

We all love our BKs but they are absolutely more complicated to run than a single air control noncat. The key word is more. English matters. Neither stove technology is terribly complicated to use when we're all experts.

 

[Ashful]

I think it's a silly argument. If moving one lever is too high a bar for anyone considering a stove, I'd argue we should take away their matches. I mean honestly... these people should not be allowed to operate basic home appliances.