A hypocaust (Latin hypocaustum) is a system of central heating in a building that produces and circulates hot air below the floor of a room, and may also warm the walls with a series of pipes through which the hot air passes. This air can warm the upper floors as well. The word derives from the Ancient Greek hypo meaning "under" and caust-, meaning "burnt" (as in caustic). The earliest reference to such a system suggests that the temple of Ephesus in 350 BC was heated in this manner, althou Hyp...
