the romans were the first people to use underfloor radiant heating systems. these systems were based on hypocausts, and used warm air for heat. the floor was set on top of many brick piles, leaving room for the hot air and steam produced by a furnace to pass underneath the floor. the hot air then went up chimneys on the sides of the walls, so the hot air and steam never actually went into the living rooms. these systems were very expensive to build and maintain, so only the rich could afford them.