19.5 hour burn time achieved

[Ashful]

Also note that flue temp going up at high burn rate is in itself not an indicator of a drop in efficiency. The temperature of everything will go up at a higher burn rate, even if efficiency remains the same. However, I do believe that Highbeam is correct for BK's, the HHV efficiencies are all lower than the LHV efficiencies.

 

[tabner]

I'm on a princess, but at higher burn rates the flue temps go way up. I agree that efficiency goes down as burn rate goes up. Still though, is the efficiency at those high burn rates still as good as a noncat? Pretty close and most of the time we're down on low output.

OK, thanks, that's reassuring. Please don't misinterpret me - even if the efficiency drops a bit, I'm still extremely pleased with this stove. I just want to make sure I'm running it as close to full potential as possible.
When you say your flue temps go way up, do you have a rough idea what range you're in? Would sustained temps on an internal probe in the 550 to 650 range be reasonable/common?

 

[Highbeam]

OK, thanks, that's reassuring. Please don't misinterpret me - even if the efficiency drops a bit, I'm still extremely pleased with this stove. I just want to make sure I'm running it as close to full potential as possible.
When you say your flue temps go way up, do you have a rough idea what range you're in? Would sustained temps on an internal probe in the 550 to 650 range be reasonable/common?

I use an internal probe and watch it carefully. Long low burns it is at 400, lower settings are possible but I feel unnecessarily low and have side effects. Medium output I'm certainly around 600-700. It can run there all day long and pretty much does whenever there's a visible flame. These medium burn rates you can really see the thermostat cycle and the flue temps seem to vary a bit more. At high burn during warm up I can pop up near 1000 since I'm burning very dry softwoods. I watch for that and do not run past 1000 which is the continuous limit for class A chimney pipe.

Short answer is yes. 550-600 all day is reasonable at medium outputs. It's still quite efficient.

 

[tabner]

I use an internal probe and watch it carefully. Long low burns it is at 400, lower settings are possible but I feel unnecessarily low and have side effects. Medium output I'm certainly around 600-700. It can run there all day long and pretty much does whenever there's a visible flame. These medium burn rates you can really see the thermostat cycle and the flue temps seem to vary a bit more. At high burn during warm up I can pop up near 1000 since I'm burning very dry softwoods. I watch for that and do not run past 1000 which is the continuous limit for class A chimney pipe.

Short answer is yes. 550-600 all day is reasonable at medium outputs. It's still quite efficient.

perfect, thank you, that seems consistent with what I am seeing. and that's reassuring. Thanks!

 

[Tron]

At high burn during warm up I can pop up near 1000 since I'm burning very dry softwoods.

I burn the same, and have to admit that when I happen to forget to watch the stove for a few minutes on warmup, it has happened that I've seen 1300-1500F flue temperature (Condar probe thermometer in double-wall flue). But as you said, the 1000F is the continuous limit, so I'm not worried. Of course, I immediately close the bypass and turn it down if I see that.

 

[Highbeam]

I burn the same, and have to admit that when I happen to forget to watch the stove for a few minutes on warmup, it has happened that I've seen 1300-1500F flue temperature (Condar probe thermometer in double-wall flue). But as you said, the 1000F is the continuous limit, so I'm not worried. Of course, I immediately close the bypass and turn it down if I see that.

To be clear, I close the bypass as soon as the cat meter goes to active or the flue temps hit 500, my high temps during warm up are with a closed bypass. I'm really afraid of further melting the bypass gasket retainers.

 

[BC_Josh]

Well, a chimney cleaner, woodstove installer came over the other day, cleaned my chimney and warned me about burning too low too often on my BK. Also, had an intake furnace vent for the gas furnace in the basement, and I was running a fan 24/7 to help heat the basement, but it was definitely causing a neg. pressure issue. Now, since I turned off the fan, the fire ROARS inside my little BK! Different feel to it, and it runs hotter which is good. Less creosote.

 

[Ashful]

Well, a chimney cleaner, woodstove installer came over the other day, cleaned my chimney and warned me about burning too low too often on my BK. Also, had an intake furnace vent for the gas furnace in the basement, and I was running a fan 24/7 to help heat the basement, but it was definitely causing a neg. pressure issue. Now, since I turned off the fan, the fire ROARS inside my little BK! Different feel to it, and it runs hotter which is good. Less creosote.

I assume he's indicating the pipe was dirtier than he'd like? How bad was it?

If the pipe was real dirty, there's a few probable culprits:

1. How long since it'd last been cleaned?
2. How old is your catalytic combustor, approximate hours of use?
3. What's your wood processing/storage situation?
4. What temperature (o'clock) do you observe on your combustor probe throughout the burn?
5. What's your chimney height and construction?
6. How far are you turning down?

The most common issues are someone trying to burn lower than the moisture content of their wood can support, or a chimney with not enough draft to keep the cat in the active when turned way down low. To hit the lowest burn rates without the combustor falling out of active region, you need very dry wood, like "under roof for 3-4 summers" dry, and you need a chimney that will keep pulling on that stove even when outlet temperature is way down low.

Cat probe temperature is your best indicator that you're trying to burn lower than your parameters will allow.

 

[BC_Josh]

I assume he's indicating the pipe was dirtier than he'd like? How bad was it?

If the pipe was real dirty, there's a few probable culprits:

1. How long since it'd last been cleaned?
2. How old is your catalytic combustor, approximate hours of use?
3. What's your wood processing/storage situation?
4. What temperature (o'clock) do you observe on your combustor probe throughout the burn?
5. What's your chimney height and construction?
6. How far are you turning down?

The most common issues are someone trying to burn lower than the moisture content of their wood can support, or a chimney with not enough draft to keep the cat in the active when turned way down low. To hit the lowest burn rates without the combustor falling out of active region, you need very dry wood, like "under roof for 3-4 summers" dry, and you need a chimney that will keep pulling on that stove even when outlet temperature is way down low.

Cat probe temperature is your best indicator that you're trying to burn lower than your parameters will allow.

First year burning on a brand new chimney and stove. So, no cleaning so far this year, been burning for a few months. Wood is at 14% moisture, all of it, larch and fir.
Combuster probe is generally at 10 c'lock to 12 o'clock through the burn, but goes higher during the initial hot burn.
Chimney looks like single walled until the ceiling, so about six feet, then goes through an insulated collar, then double walled stainless steel though an attic for about 7 feet, then a few feet outside, also double walled stainless.
I've been turning down the thermostat, generally to a 3 o'clock position, or 3:15 position. When I turn it up to about 4 o'clock or 5 o'clock, it turns my house into a sauna, unfortunately.
Thanks for the response.

 

[BC_Josh]

I should also mention that the report filled out by the chimney cleaner stated that the buildup in my chimney was "average."

 

[Ashful]

Combuster probe is generally at 10 c'lock to 12 o'clock through the burn, but goes higher during the initial hot burn.

If you're keeping that combustor probe temp up around 10-12 o'clock, you're good. Yeah, these stoves can make the chimney a little dirtier than a non-cat, but no worries. You'll also notice that the amount of dirt at the end of a season is really not much more than that just a few weeks in, it's not a linear progression of build-up. If you're like most of us, all dirt will be isolated to bottom 3 feet and top 3 feet of the pipe, with everything in-between totally clean.

I wouldn't worry about anything, based on what you're reporting here.

 

[BC_Josh]

If you're keeping that combustor probe temp up around 10-12 o'clock, you're good. Yeah, these stoves can make the chimney a little dirtier than a non-cat, but no worries. You'll also notice that the amount of dirt at the end of a season is really not much more than that just a few weeks in, it's not a linear progression of build-up. If you're like most of us, all dirt will be isolated to bottom 3 feet and top 3 feet of the pipe, with everything in-between totally clean.

I wouldn't worry about anything, based on what you're reporting here.

Thanks for the input. Although, the chimney cleaner figured I was running my stove too low, when I turn the thermostat up past 3:15 to 3:30 o'clock (just past halfway, or just past the low burn setting), my little house becomes an almost unbearable sauna it gets so hot in here.

Actually, I think the probe doesn't get under 12 o'clock. Even with embers in it, it's usually almost there, maybe a bit lower, but usually if it is, there aren't enough embers left to start another fire with.

 

[Ashful]

Must be a relatively new combustor. Once broken in, they usually drop out of active late in the burn, coaling stage. But all of the moisture and most of the creosote-generating compounds are burned off by then, so no harm.

A SootEater rotary cleaner is a good and relatively cheap investment for most running a stove on a regular basis. With that, you can quickly and easily clean a few times per year, to get a sense of how you're treating that chimney. If you're like most of us, you'll get to where an annual cleaning is all that's really required, but it's never bad to do more often on a new rig, until you're satisfied it's burning clean.