Hypocaust

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.[1] 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,[2] although Vitruvius attributes its invention to Sergius Orata in c. 80 BC.[3] Its invention improved the hygiene and living conditions of citizens, and was a forerunner of modern central heating.

Hypocaust under the floor in a Roman villa in Vieux-la-Romaine, near Caen, France