Harman Hot Air SF-3500-A Furnace

Does anyone use a Harman SF-3500-A and if he or she does could I get some remarks on the performance and a comment on the brochure on how it says it can go from being a wood burner to a coal burner in one easy switch. My fathers got one of these and he is gonna buy some coal for it, he's been burning wood for the past 9 years in it. and I want make sure I know something about this unit before I go over there and explain to him about not messing with it when he tries to get the coal going. thanks .