I burned coal for heat for a couple years, before my chainsaw addiction took over. My furnace that I have now will burn coal, only done it a couple times. My other coal stove was a stoker, that was a handy device for sure. My dad used to burn both a coal stove and a coal boiler at his business Used to have to tend the stove, hated carrying bucket after bucket of coal up the stairs.
As others have said, the bottom draft is crucial when burning coal. A stove designed for coal is essential, anthracite really can throw heat. I just got tired of dealing with cinders all the time, and a lot of them at that.
Also keep in mind that coal doesn't make much of a draft, and higher outdoor temps make it worse. You should never burn coal over 55F outdoor temps, won't be enough temp. difference to produce draft. My aunt and uncle almost died this way, they'd been burning coal for 50+ years. CO detectors are much more likely to activate while burning coal, just because of the low flue temps and draft. No creosote, though it will eat black pipe in a year or two. Make sure your pipe is rated for all fuel or coal.
Coal can throw lots of heat if burnt correctly, or it can fill your stove with hot stinky rocks that you have to dig out. There is a steep learning curve, but it is well worth learning if you want to heat this way.
A few chunks on a wood fire shouldn't hurt anything, though.