Ondol heating - The ondol floor was made from packed earth covered in paper. Hot smoke was then passed along channels beneath the floor to heat the room. Ondol floors were used in rooms of the main living quarters. Every private residence of traditional Korea, no matter how humble, was equipped with a heated ondol floor and a kitchen for cooking, which was essential during Korea's cold winters. Kang bed-stove heating - The Kang is a traditional long (2 meters or more) sleeping platform made of bricks or other forms of fired clay and more recently of concrete in some locations. Its interior cavity, leading to a flue, channels the exhaust from a wood or coal stove. Typically, a kang occupies one-third to one half the area the room, and is used for sleeping at night and for other activities during the day. A kang which covers the entire floor is called a dikang, di meaning "floor". Hypocaust heating - A hypocaust was an ancient Roman system of underfloor heating, used to heat houses with hot air. Many examples of such hypocausts exist in villa and house foundations in Roman centres in Germany and England. The usual custom was to lead the hot air from a hypocaust into a single vertical flue in the wall of the room to be heated, through which the hot air and smoke escaped into the open air. Where greater warmth was desired, several flues would lead up from the hypocaust in the side walls of the room; at times these wall flues consisted of hollow, oblong tiles, set close together, entirely around the room. Requirements: - Not solely associated with baths - Constructed before 750 AD