Catalytic Combustor Questions

[begreen]

I always read that above 1600 f it gets dicey. But new cats often are very active (=hotter), and will settle down after some time. (Due to the changes resulting from that hyperactivity.)

I believe that is correct from what I recall Chris saying.

 

[Woody Stover]

I believe that is correct from what I recall Chris saying.

Yeah, and he was talking about, I forget the term, but a smoothing of the catalyst surface so that the smoke can't contact it as well. He knows quite a bit about them.

 

[Mike the heater]

Only thing I can think is that when the cat housing glows, it distorts and opens up some leaks where smoke gets past the cat.
How active a burn do you usually keep going? Medium to large flame in the box?
I have a Dutchwest with a similar setup, cast iron cat flame shield below the cat, then the 8x2" round cat is wrapped in interam gasket and drops into a "cup" that holds it. To get that cast iron shield glowing, cat has to be orange and I'd have to have pretty strong flame going in the box. If I have a cat-only burn, no flame, the cat shield doesn't glow. I never saw any cat probe temp above 1200-1300. The Buck 91 would try to push above 1500 on occasion, no flame in the box, but I would nip that in the bud when it happened.
Do you need flame going in the box to be able to heat your place, or will a cat-only burn do the job?
What kind of wood do you generally burn? If it's lightweight wood that burns faster and feeds the cat more volatiles, quicker, that will cause the cat to burn hotter. Dense woods like White Oak or Black Locust burn and gas slower, so are less of a problem in that regard.
With your new cat, was there interam gasket supplied, that wrapped around the cat? Is it an OEM cat? Some cats are wrapped in interam, then a stainless band is wrapped on top to hold the interam gasket in place. I'd guess the cat was made by Firecat (Applied Ceramics)...?


Yeah, but you're BK guys. You're commanded to keep your hands off things like stove air control/cat temps (no numbers on the probe dial,) let the stove run itself, and not worry your pretty little heads about such things. 😏 Unless you have a probe in your stoves, cat temps are a moot point for you.

I keep a medium flame, but only now that I'm having this issue. I used to keep it hotter. Flames COULD be the problem. My new cat did not come with a gasket. The only gasket is between the cat housing and the top of the firebox. There's no gasket on the vertical sides of the cat. I can't recall the brand name, but no its not OEM. But it fits perfectly and is same dimension as the one I replaced. 7" diam x 2" high. It's made of steel.

A cat burn at 1200 - 1600 is fine. But I like to stoke it higher and leave it be for 4 - 5 hours. But then it gets hotter, over 1600. My wood is good and dry. Mostly its doug fir, about 1/3 is black oak. A few piece of pine and cedar here and there.

Stove gets a good draw for stoking and starting. But, ya never known, there might be something stuck in my chimney. There is currently an honest 5 feet of snow on my roof, Nor Cal at 4500' elev. So I'll have to check that later.

 

[Ashful]

Not sure if Ashful runs a cat probe, but I don't think so...?? You'd think he would, nerd that he is.. 🤓

My experience with overheating, distorting, and even flat-out melting cat combustors all comes from the three Jotul Firelight 12's I owned before the present pair of BK's. They were horribly unreliable and finnicky early up-draft cat stoves, designed in the late 1980's and sold roughly 1990 - 2000. They were outfitted with thermocouple probes fed into digital recording meters, so yeah... usual nerd stuff.

I saw many cat temps over 2000F on those old Jotuls, and often even up to 2200F. I think the record high I ever recorded was a one-time excursion above 2600F, when the thermocouple probe melted and failed, so no one really knows how high it went after that. The entire back of the stove was glowing for a few hours, despite having 3/4" of refractory insulation board between the combustor and stove back. I stopped using the Jotuls for any serious heating, and placed an order for the present BK's, the day after that event.

But you are also right about the BK's, they're simplicity at it's finest. I see no need for such rigorous monitoring of a well-designed stove, they truly take care of themselves.