I have decided to buy a coal stoker boiler to replace my oil burner. My heating system is radiant floor and domestic hot water is via indirect water tank which pulls heat from the boiler primary loop. Chimney is class A, 6", 30'+ tall, drafts extremely well. I refuse to replace it.
The house - is 6 years old, 2,300 sq.ft., 2 floors with great room cathedral ceiling. Insulation is R-35 roof, R-28 walls, R-22 basement walls. The basement (1,400 sq.ft.) will eventually have radiant tubing under a raised subfloor. Backup heat is from 2 wood stoves, one in the basement, one in the living room. Either wood stove will heat the house OK. 3 different heat loss calculations are showing 63,000 - 83,000 BTU/hr which includes the basement. The boiler will be in a basement mechanical room so standby losses will at least heat the basement.
I just started doing research on coal stokers as well as reading this forum. I'm not set on any one brand or model yet. But, based on the physical size of the units, the space available for installing one, and my BTU requirements, I'm leaning towards a Keystoker KAA-2, KA-6, or Harman VF3000. At the risk of repeating questions that have already been answered a million times, here goes...
KAA-2 (76-90K BTU/$3650) - Seems big enough and would operate closer to it's rated capacity which is good for efficiency. I'm not too keen on the small 100 lb. hopper. The 6" breeching matches my chimney without an adapter. My dealer has an unhappy KAA-2 customer complaining that it doesn't heat his small ranch house properly. I would guess that it's not the stove but the rest of his system causing the problem. He is steering me towards the KA-6.
KA-6 (122-144K BTU/$4,5180) - Seems to be more BTU output than what I need but maybe that shouldn't heavily influence my decision? I like the large hopper/less frequent fill/empty cycles. Keystokers burn both rice and buckwheat, even when a bit wet. Dealer suggests a mix (Reading Anthracite). The 8" breeching would require an adapter to 6". Will this unit still perform well with a 6" chimney? Availability of the Keystokers is 10 - 12 weeks.
Harmon VF3000 (95K BTU/$4820) - looks well made, perhaps a notch above the Keystokers in appearance/fit & finish/design details (the pusher mechanism pivots on bronze bearings with oil cups and the cam arm has a ball bearing pushing on the yoke - that's nice! Keystoker is plain steel on steel). 7" breeching would require an adapter which I already have for my oiler's 7" breeching. Again, will the VF3k run well with a 6" chimney? Burns rice coal only! Buckwheat can jam the feeder. Availability - in stock. I can have one tomorrow.
Will the chimney gases/particulates damage my steel roof?
Do I need to run my primary loop at 180 - 190F like I do with my oiler and keep the return loop water above 140F?
I’m sure I’ll have more questions soon. Thanks to all for taking the time to respond.