DrP - is your coal furnace dirty and a PITA to clean? I am seriously considering switching to a pellet or coal boiler/furnace. Coal is a cheaper option, but I've heard it can be a chore to keep clean. The new pellet furnaces are pretty clean and mostly hands off, but they are a LOT more money.
Actually, we have a pellet stove in the garage, but didn't use it this winter. I found the pellet stove to require a bit more maintenance than the coal stove. With that, about every other week, it had to be shut down & vacuumed out to keep things clean inside. With the coal stove, I usually shut it down around mid-winter, vacuum out underneath where the fire is, clean the fans, and pull the stove pipe out of the chimney to clean out any ash that's accumulating there. Takes me 15-30 minutes to clean. It's my wife's job to empty out the ash pan - if she forgets, and it overflows, then we get quite a bit of fine dust in the house when she takes it out of the coal stove.
From outside the house, there's no sign that we're using coal - no smoke or anything like that. Since the coal is dampened prior to bagging, there's no dust at all when the coal is dumped into the hopper. There's some annual maintenance, but it's not that difficult. As easy as it is, I was just considering grabbing a discounted pellet stove that's on sale for only $1200ish. Or rather, my wife was considering having me do that. I can pick up coal by the ton only about 1/2 mile from my house, so it's convenient.
When we first started burning coal about 8 years ago, it was around $120 per ton. This year, it's $260 per ton. (anthracite) Last year, it was $290 per ton. So, it costs around $10 per million BTUs. Hardwood pellets, on the other hand, if purchased off season, are around $180 per ton; roughly $14-$15 per million BTUs. So, coal is still more economical than pellets, but not by nearly as much as it was a few years ago. On the other hand, when compared to electricity... at 10 cents per kilowatt hour, that's just shy of $30 per million BTUs. Oil and propane are both well into the $20's per million BTUs. So, $2 or $3 really isn't that much. Firewood is actually cheaper per million BTUs. However, once you factor in the efficiency of the coal stoves and pellet stoves, compared to the efficiency of wood stoves, (iirc), coal still beats firewood, though not by as much as it did 7 or 8 years ago. Back then, when I was shopping for a wood stove, I was quickly convinced to get a coal stove by doing the math that realized that I could still cut all my own firewood, but then, sell the firewood, buy the coal with the profits, and have money left over for a couple nice dinners out with my wife. Of course, wood stoves are cheaper than coal stoves, so it would take longer for it to pay for itself. AND, most importantly, wood stoves have to be stoked quite frequently. The coal stove, if I turn it back a lot, can run for about 3 days on a hopper of coal. Ditto the pellet stove (maybe even 4 days for the pellet stove.) But, I can store the coal anywhere - rain or snow isn't going to destroy them. Pellets have to be stored where the environment is controlled. Wood - can't go away for 2 or 3 days and have the wood keep the house warm.