I've had a C-28 since 1987. That unit was bigger than required by the sq footage of my house, but had a 24" deep firebox....better for wood, and allowed for a future addition and/or heating the garage. Burned wood, six chords of white & red oak each winter for first 5 or 6 years....I over-sized the baseboards by an additional 50% (if room needed 12', I installed 18'). Consequently I had to burn a 'cold' fire, running water at only 140deg or got chased out from the heat. Note that I don't have electric zone valves. I use manually adjusted gate valves. I got too old and lazy to mess with that much wood, so for the last 20 yrs I burn wood in spring and fall, and coal all winter.
I only burn Bit coal, especially after seeing the aftermath of unattended or poorly attended boilers and anthracite coal. A friend of mine TOTALLY MELTED 3 cast iron grates when he inadvertently neglected to tightly close the bottom door after removing ash. The worst that ever happened to me from that nishap was popping-off the pressure valve.
I have burned too many different types of coal to mention, but I will tell you this. If you can find a coal-yard or private individual with an open strip on his property that is what is referred to as Nine-Foot Pittsburgh coal, you will get maximum heat, minimal ash, little or no 'grate clogging' slag or slate, and it is CHEAP !!.. as of winter 2013/2014, 'private' 9' goes for $60/ton, and 'coal-yard' price is $70. Nine ft run-o-mine with about a 50/50 mix (half slack (fine) coal and the rest from gravel to lump) is what you want. Do not let the appearance fool you. It looks horrible....like a dirt-filled mistake with yellow sulfur stains and thin flaky layers, but it will burn you out of the house. Very little soot in the pipes and chimney, and the ash is about 1/3 of the coal. That 'pretty' bright, shiny screened, 'nut' coal looks nice, but it is all about performance.....isn't it?
I live in the PA mountains about 20 miles from the highest point in PA (Mt Davis).... It has been between zero and 13 BELOW ZERO for the past 3 days and I burned an average of three and a half (3 1/2) 5 gallon buckets per 24 hrs. In typical winter temps (teens to 30's) I burn 2 to 2 1/2 buckets per 24 hrs. Coal is in a bin outside and I bring in buckets as necessary. FYI, the perfect 'loader' for the Chappee is NOT a shovel. It is a rectangular plastic kitchen trash can cut on a 45 degree angle with a utility knife. It holds one 5 gal bucket of coal, fits perfectly in width of the small Chappee door, and loads the firebox on an angle from front to back in one quick shot....perfect 'banking' to burn all day and again all night. The door is only open for a few seconds, so if any smoke blows back it is minimal. A 'commercial' 8" dia. kitchen exhaust fan with a cable operated trap door outside takes care of the rest. Home centers have them. Don't burn coal without one. I never close the trap door.... I enclosed the boiler in a seperate space w/ cement-board walls and steel tile ceiling, and the open fan pipe supplies air for the boiler w/o pulling it thru every leaky door and window in the house.
Pgh 9'.... light it up.