Update on cherry pits as heating fuel
At last, we're on the downhill side of winter. Or is it the uphill side? Anyway... it's finally warming up a bit, but over the course of this somewhat grueling winter, we've had plenty of opportunity to experiment with heating our house with cherry pits.
It's really interesting to see the differences in the various fuels. Well, okay, maybe not to everybody. But just in case others are in a similar position, I'll share what our experience has been....
Cherry pits don't produce the same grainy ash that corn does, nor the light fluffy ash of the wood pellets. They're somewhere in between. You don't get very much ash falling down into the ash pan, but you get quite a bit floating around and sticking to the walls of the burn chamber, and the exhaust vent. It varies from a grayish tan to a sooty black. A poor burn (i.e. not enough airflow) gets you something akin to creosote coating everything.
While mixing corn and wood pellets gets you the best of both worlds, mixing cherry pits and wood pellets gets you the worst of both worlds. (I didn't have a chance to try mixing cherry pits and corn.) The pellets plus cherry pits initially looked good, since there was almost no ash in the ash pan. I thought we were getting a more complete burn, amounting to higher efficiency. What was actually happening was that there wasn't less ash, it was just more airborne ash. More ash collected on the heat exchanges, in the air intake and exhaust ducts - basically in a lot of nooks and crannies, which meant the airflow was poor, which meant the efficiency was getting worse and worse over time.
It got bad enough that the air intake fan wouldn't turn any more (though I'm sure some of it was from the previous two winters). I had a service tech out to help troubleshoot. He showed me some new tricks for cleaning & maintaining the stove. But even with good airflow, I have to knock ash out of the exhaust duct about once every couple days to keep it from building up again. And it still builds up in hard to reach spots that are more suited for a spring cleaning project than a weekly maintenance task.
The other problem is that - contrary to what I'd heard - the cherry pits burn a little more slowly than pellets or corn, which, without getting into too much detail, means that we can't set our stove to it's highest setting. We can run wood pellets on 5 (the highest setting). We can run corn on 4 and get more heat than pellets on 5. If we run cherry pits on anything higher than 3, it will work for a while, but get worse over time. By the time 8 hours is up, the burn pot has filled up, the fire is partially smothered, the heat output is down, and there's smoke coming out of the exhaust vent - something that never, ever happens with corn, and rarely with pellets.
I wanted to like the cherry pits. And they were usable. Our heat stove just doesn't cope with them all that well. They don't produce noticeably more heat than wood pellets (unlike corn, which does produce noticeably more heat). They do produce noticeably more ash in the least convenient places.
Our first winter with this heat stove, we burned primarily corn. Last year we used about a 3:1 mixture of corn & pellets, but then straight pellets at the end of winter when the corn ran out. This year, we didn't use any corn. After bad experiments mixing corn & cherry pits, we went back to either/or. Next year, I'm going to say it's back to the corn/pellet mix. Each fuel has it's good and bad points, but the corn/pellet mix seems to result in the cleanest, hottest burn while staying on the low end in terms of cost and hassles.