I have the user manual online (http://cemrweb.cemr.wvu.edu/~mathews/boiler/
). In the manual it mentions only the use of anthracite coal, not bit. I have yet to obtain some anthracite coal to try (I'd love to have some), but the bit coal works very well. Its taken me most of the season so far to learn how to fire it properly--advice from others here was most helpful--but it just takes experience I think more than anything else.
I have a 6 inch chimney pipe and that's apparently too small--I clean it out every couple days to unclog the soot buildup. When the fire is really hot and burning well, you can put a load of bit far in the back and the soot/gases then mostly burn up as they travel to the front to get out. This can only go on so long though since the front coal will burn down and the back coals get too high. Using a tool to pull the hot coals up front helps some, but then the coals break up and fuse together causing the fire to cool down where the coals have been moved.
My best luck so far has been keeping the firebox pretty low (2 3 inches of glowing coals) and putting 1 to 2 shovel loads directly on top of that bed. This makes some smoke for a few minutes only, then burns quite cleanly. The hotter the fire when you load it, the less smoke goes up the stack. Where I get the most soot is when the water temps come up to the limit and the damper door closes. Then the coal bed 'stews' without much air and much soot is produced it seems. This happens at night when I really load the boiler up to try and last all nite--I get it really hot, then put in 3, 4, even 5 shovels of coal (30, 40 lbs). This all but smothers the fire and makes much smoke. What happens though is in about an hour the new coal is done swelling and then the fire coasts for several hours, thus getting me through most of the night.
I would think that if anthracite coal was used this would all be much easier, but then the grass is always greener . . .