I have an antique parlor stove that I've retrofitted for improved (wood burning) efficiency and safety. I've used it in modified form for quite a few years and am happy with its performance.
However, it has been a nasty winter here in SW Wisconsin, and my wood supply is running low. I am thinking - as an experiment - of trying to burn coal in the same stove, as a supplement to wood.
I don't as yet know what type of coal (if any) might be available locally.
Not too far from Madison is Pardeeville, where you will find an Amish community; which uses and sells coal. Since they use the gravity flow stoves, it might be the nut size of Anthracite. In Mukwonago along I-43 a business by the name of Horn Feeds Inc, located at 728 Claredon Ave. (262-363-7116) has the soft coal that would work best for your application. I know because I went and bagged some for myself and a farmer friend, who was correct that it starts easier and doesn't fall through the grates.