Subbituminous coal is a dull black coal with 35-45 percent carbon content and a heat value between 8,300 and 13,000 BTUs (British Thermal Unit). Reserves are located mainly in half-dozen Western states. Subbituminous heat value is lower, and it has lower sulfur content than other types of coal. Subbituminous makes it a cleaner burning coal. Subbituminous coal is mainly used for electricity and heating homes.