Radiant heating, as opposed to warm air systems (such as a forced air unit heaters), deliver the source of heat to the floor level, not the ceiling. And since warm air rises, heating the floors proves to be the most efficient means of heating living areas.
Radiant floor heating or radiant energy is the oldest form of heating used to provide comfort and is the basis for all heating systems. Radiant energy is totally pure radiation and is absorbed by an object without physical contact with the heat source or by heating the surrounding air, as is the case with convective, forced air systems.
Under floor heaters were first used by the Romans. Initially the preserve of the rich, under floor heating became increasingly commonplace in public buildings and villas, particularly in the colder regions of the Roman Empire. The Roman system was based on hypocausts, comprising ducts that underlay the floor (itself built on raised brick piles) and flues that were built into walls. Hot air or steam from fires circulated up through this system, warming the floor and walls, with heat passing into the rooms.
More specifically, the floor was laid out as series of concrete slabs acting as radiant heaters supported by columns of layered tiles, with a furnace at the bottom of one exterior wall. By placing the fire here, the draught would take the radiant heat under the floor, and up through the walls to radiant heater chimneys located in the corners of the room.
Today we recognize the brilliance of the Romans and Koreans as early adopters of radiant heating, as the technology is still a desired method for delivering comfortable and efficient heat in our homes. Now we have radiant heaters using electric resistance cables that are constructed of highly rated materials and feature manufacturer warranties of up to 25 years.