As I understand it, coal burns very differently than wood. It requires an enormous draft, much more than a wood fire. A modern, efficient wood stove would be unlikely to provide enough air unless you kept the door cracked open.

Every coal stove I've seen, ancient or modern, holds the coal on a massively heavy grate so the draft can swirl all around it and the ash can fall away.

Coal also creates a very intense spot of heat as it burns. (Think blacksmithing: coal + draft = nearly molten steel.) Modern wood stoves would be vulnerable to damage since neither the brick nor the metal below could take that intense heat.

I wouldn't consider using coal in a wood stove unless I added a couple extra layers of brick below and a heavy steel plate for the coals to sit on. I've been thinking about welding together an insert out of 1/4 inch plate steel, with a grate above. But I'm still not sure about the draft issue.

Even then, it would have to be a genuine emergency, as it would instantly void any warranty on the stove.

P.S. BobS, Congrats on your endless wood source. Nice. Free heat warms you from the inside as well as the outside.