It is used to regulate drafts and to prevent heat loss up the chimney, when the fireplace is not in use. The walls and back of the firebox are generally angled in to radiate heat back into the room. The inner hearth is made of firebrick or steel, and holds the burning fuel. The outer hearth protects the floor from heat and sparks. Two types of heat Fireplaces and stoves produce two different types of heat - radiant and convection.
Radiant heat is the transfer of heat to solid objects in a room.
Radiant heat does not heat air space, but just the objects themselves. Convection heat is produced by heating the air and circulating it around the room. Some convection fireplaces, known as heat circulating models, use a blower to circulate the warm air. Direct Vent Technology Direct Vent fireplaces have an air tight firebox that draws air for combustion from outside your home, never stealing the warm air from inside, yet radiates and convects heat into the room. These fireplaces can be vented either from the top or the rear.