English

Etymology

Latin hypocaustum, from Greek hypo "underneath" + kaiein "to light a fire, burn"

Noun

1. an underfloor space or flue through which heat from a furnace passes to heat the floor of a room or a bath, as illustrated by the ancient Roman hypocaustum, and the traditional Korean ondol (온돌, 溫突).
2. an underfloor heating system, even without such an underfloor space or flue, as adapted to the modern housing, east and west.

Synonyms

• floor heating
• underfloor heating

A hypocaust is an ancient Roman system of central heating. The word literally means "heat from below", from the Greek hypo meaning below or underneath, and kaiein, to burn or light a fire. They are traditionally considered to have been invented by Sergius Orata, though this is not fully confirmed.

Operation

Hypocausts were used for heating public baths and private houses. The floor was raised off the ground by pillars, called pilae stacks, and spaces were left inside the walls so that the hot air and smoke from the furnace (praefurnium) would pass through these enclosed areas and out of flues in the roof, thereby heating but not polluting the interior of the room. Rooms requiring the most heat were placed closest to the furnace, whose heat could be increased by adding more wood. It was labour-intensive to run a hypocaust as it required constant attention to tend the fire, and expensive in fuel, so it was a feature of the villa and public baths.

Vitruvius describes their construction and operation in his work De Architectura in about 25 BC, adding details about how fuel could be conserved by designing the hot room or caldarium for men and women should be built next to one another, adjacent to the tepidarium so as to run the public baths efficiently. He also describes a device for adjusting the heat by a bronze ventilator in the domed ceiling.

The hypocaust is generally regarded as a major Roman invention which improved the hygiene and living conditions of citizens, and was a forerunner of modern central heating.

After the Romans

A derivation of hypocaust, the gloria, had been in use in Castile until the arrival of modern heating. After the fuel (mainly wood) has been reduced to ashes, the air intake is closed to keep hot air inside and slow combustion.

Korean traditional houses use an Ondol which is similar to a hypocaust, drawing smoke from a wood fire typically used for cooking.

See also

• De Architectura
• Roman engineering
• Roman technology
• Ondol
• Gloria in the Spanish Wikipedia.
• Kachelofen in the German Wikipedia.
• Kang bed-stove
• Vitruvius

External links

• About Roman baths (referring to Sergius Orata), by William Smith.
• Disputing the priority of Sergius Orata Garrett G. Fagan's paper "Sergius Orata: Inventor of the Hypocaust?" published in Phoenix, Vol. 50, No. 1 (Spring, 1996), pp. 56-66
• Hypocaust heating Wordreference.com
• Roman central heating: the hypocaust
• Diagram of a Roman hypocaust system
• Hypocaust
• How to build your own hypocaust Channel 4 Time Team project