cat went out first year on the buck , been burning without cat last 2 years , didnt seem it helped much with heat output , maybe just cleaner chimney , having 3 different people run the stove didn't help the life of the cat,
I found that with the cat, I could run low, maybe a little flame in the box, but the cat would be blazing on the smoke and I couldn't hold my hand in front of the blower outlet for more than a couple seconds. When cruising the stove, I had the shotgun air (left slider) closed and the right slider pulled out maybe1/8-1/4". You should get more heat out of each load that way. The slower the air is moving through the stove, the more heat it can extract from the exhaust.
And yeah, the chimney didn't get very dirty with the cat working. I miss that stove.
My problem was, I didn't have enough control over the air, and cat temp would be pushing 1800. The cat won't last long when you run 'em that hot. I liked to see between 1100 and 1500 on that cat probe dial.
One problem was air leaking at the ash pan gasket. You can tell that's happening when the coals over the ash dump lid are glowing more brightly than the other coals in that area. I had to re-do the gasket to make sure it hit the ash pan housing squarely, and that there was no gap where the ends of the gasket came together.
The other source of too much air was that the plates on the right-side air control slider weren't sealing off the openings tightly. Another Buck 91 user had the idea of removing the plates from the rod, taking the rod out, and bowing it up slightly in the center, so that it holds the plates closer to the openings. I heard that idea too late for my time with the stove. But I did put some shims in the rod holders, which raised the plates closer to the holes.
Now, if you get the plates sealing off the holes better, there's a risk that you might crash the cat if you cut the air too far. You need to know what you are doing to run the stove well..took me a while to figure it out.
I was trying to heat my MIL's house with the stove not centrally located, 9.5' ceilings, and no wall insulation. I had the second story blocked off with a curtain across the doorway.
Sounds like you may need a wood furnace or boiler in that place, though..