If his OWB is setup with grates and any kind of an ashpan/underfire air he will be able to use coal in it "as-is". However, using coal dierecly in an outdoor boiler will produce smoke, it will be relatively inefficient (i've seen flames three feet high from their stacks when burning coal and the fan kicks on) and he'll still have to do a lot of shoveling. There's something I forgot to mention in my last post- the ideal thing would be for him to sell his boiler and install the "coal-man" outdoor stoker boiler- it's a package unit that's simple to operate and is very, very nice. there's a member: outdoorcoalboilersofky that sells them, he may be able to offer you a price. The only caveat with his boilers is that unlike a traditional underfeed stoker, his are self-ashing w/ a rotating ring and require a low coke-button coal, in Western pa this means paying around $80-$90/ton to find a coal w/ 4 cokebutton or less.