hypocaust

Floor raised on tile piers, heated by hot air circulating beneath it. It was first used by the Romans for baths about 100 BC, and was later introduced to private houses.

Hypocausts were a common feature of stone houses in the colder parts of the Roman empire, but could not be used in timber-framed buildings. Typically the house of a wealthy person would have one furnace heating several rooms. In larger houses there might be several such furnaces, and during the 1st century AD channels were built into walls and roofs in order to distribute heat more evenly around the building.