A grate sized for the type of coal to be used is
necessary to support the fire and supply draft. More
draft (pressure required to move air) is needed to
burn coal because air is drawn through the tightly
packed ash layer and bed. A larger or taller chimney
may be needed or, in the case of high output units, a
forced draft can be used. The draft control system on
the heating unit should be designed to supply most
of the air as primary air below the grate, just the
opposite of the wood unit. One advantage to coal
as compared to wood is that no creosote is formed,
eliminating the potential for chimney fires