Ondol is a uniquely Korean heating system that can be traced back to the ancient kingdom of Goguryeo. Unlike Western heaters that generally warm the air, ondol heats the floor of a room. Invented by ancient Koreans, the original system worked by heating a large stone under a living space: Smoke from a fire just outside the dwelling was forced under the stone and exited on the other side. The system survives today in modern houses and apartments where water heated in gas or electric boilers is circulated through pipes encased in cement floors.
