Run-of-mine is different depending on how the coal is mined, the initial crusher, and the particulars of the coal itself. Some ROM has lots of fines and small sizes, some doesn't. With bit coal the largest sizes you can easily fit in your boiler are the best sizes to burn. When ROM is burned, often there are too many smaller sizes that pack around the larger ones thus obstructing air flow and causing very poor burns with certain coal. If you want to buy ROM and then pick out only the larger chunks (baseball size and larger) to burn in your boiler, you will probably be alright.