In response to Isayre's question on "coke button":
Coke button and FSI or Free Swelling Index are basically interchangable terms that not many understand, but, relay perhaps the most important quality a bituminous coal possesses for home heating use. Coal is basically heated in a dish in controlled conditions and the propensity of it to expand and "melt" is examined. It is then given a numerical rating based on the size of the coke left in the dish. The amount the coal expands is rated from 0 to 9. Nine is a strongly coking coal (highly expanding/melting) and 0 is a totally non-coking coal.
Most Eastern KY and some Southwestern WV coals will be 0-2 coke button which is ideal for home use. Most ohio and western PA coals will be 3-7 coke button coals, while most Maryland and Virginia coals will be 7-9. There is no other quality in coal which can definitively predict a low or high coke-button, some high volitile coals will be low, some will be high, and the same is mostly true for mid and low volitile coals, however, mid and low volitile bituminous coals will likely have mid to high coke buttons.
Interestingly enough, it is often the perception that certain eastern mid or low volitile coals are "good bituminous coals" because of their low volitile content and high btu's. This often creates so much confusion and frustration when trying to burn them because while they may be "good" as in "low smoke" bituminous coals, they are not "good" coals for home use because they fail in the very important area of caking/coking tendency. For home heating use, anything over 6 will be a pain and anything under 2 will be ideal.