Ondol

Ondol is a traditional Korean underfloor heating system that channels heat and smoke from a wood-burning firebox, called an agungi, beneath a raised masonry floor through a network of horizontal flues before venting it out a freestanding chimney on the far wall, warming the floor slab itself rather than the air above it. Evidence of the underlying gudeul flue technique reaches back to a Neolithic dwelling in Sonbong dated to around 5000 BC, and a possible early example survives at a site in Unggi dated to roughly 1000 BC, though the oldest ondol installations that can be dated with documentary confidence are from the twelfth and thirteenth centuries AD. What began as a heating method for a single room expanded by the eleventh century to warm entire floors of a home, and the system became especially widespread during the cold sixteenth and seventeenth centuries, spreading to ordinary households by the late Joseon dynasty; coal briquettes replaced wood fuel from the 1960s, and by the late 1970s modern hydronic systems circulating hot water through the floor had largely replaced the traditional hot-air flues.