Hypocaust

[7] Rooms intended to be the warmest were located nearest to the furnace below, the heat output of which was regulated by adjusting the amount of wood fed to the fire.

It was expensive and labour-intensive to run a hypocaust, as it required constant attention to the fire and a lot of fuel, so it was a feature usually encountered only in large villas and public baths.

Vitruvius describes their construction and operation in his work De architectura in about 15 BC, including details about how fuel could be conserved by building the hot room (caldarium) for men next to that for women, with both adjacent to the tepidarium, so as to run the public baths efficiently.

In 1984–1985, in the Georgian Soviet Socialist Republic, excavations in the ancient settlement of Dzalisi uncovered a large castle complex, featuring a well-preserved hypocaust built between 200 and 400 BC.

[8] Korean houses have traditionally used ondol to provide floor heating on similar principles as the hypocaust, drawing smoke from a wood fire typically used for cooking.

In colonial British North America, the house of Maryland governor Charles Calvert (now part of the Historic Inns of Annapolis) was constructed in the 1720s with a hypocaust to heat a greenhouse for growing tropical plants.