Coal choices are like trucks. Everyone has a favorite. I find it hard to believe anyone is going to sell poor quality coal for any length of time before going out of business. Coal is like a good dinner. If you like it you tell some people, if you hate it you tell everyone. With stokers coal quality is a concern but not nearly as much as a hand fed. I ran a Buderus hand fed for 27 years and fought with coal I bought from time to time. I now have a Keystoker 90 top vent and Coal-trol and it is coal burning on cruise control! Yes some coal falls off the grate in chunks known as clinkers and some other is like powder. White ash and red ash are the types of coal you will deal with. White ash produces a fair amount of fly ash, which requires you to monitor your exhaust passage ways a little more than red ash. If you research white ash and red ash many will have opinions either way. Take a look at the posts and you will be able to make your own judgements. Good luck and may the "heat be with you".