hypocaust
noun
°An underfloor space or flue through which heat from a furnace passes to heat the floor of a room or a bath, as illustrated by the ancient Roman hypocaustum, and the traditional Korean ondol (온돌, ).
°An underfloor heating system, even without such an underfloor space or flue, as adapted to the modern housing, east and west.
synonyms: hippocaust, floor, heating, underfloor