Underfloor heating is a building technology which achieves indoor climate control primarily by circulating heated water or by electric cable, mesh, or film heaters.
In pre-Roman times underfloor heating was a rare and somewhat radical technology in a world that typically relied on open fireplaces. But not only were fireplaces inefficient in warming an entire room, they were dangerous as well from the risk of fire and smoke inhalation.
Underfloor heating was used by the Romans but was invented by the Koreans in the Bronze Age. Initially the preserve of the rich, underfloor heating became increasingly commonplace in public buildings and villas, particularly in the colder regions of the Roman Empire.
The Roman system was based on hypocausts, comprising ducts that underlay the floor (itself built on raised brick piles), and flues that were built into walls. Hot air or steam from fires circulated up through this system, warming the floor and walls, with heat passing into the rooms.
The hypocaust continued to be used in the Mediterranean region during late Antiquity and by the Umayyad caliphate. By the 12th century, Muslim engineers in Syria introduced an improved central heating system, where heat travelled through underfloor pipes from the furnace room, rather than through a hypocaust. This central heating system was widely used in bath-houses throughout themedieval Islamic world.
Castile in the Middle Ages
The gloria was inspired by the hypocaust and continued to be used in Castile until recent times.
In contrast to the eventual disappearance of the Roman underfloor hypocausts, underfloor heating has remained in use for millennia in Korea, where it is known as ondol. It is thought that the ondol system dates back to the Koguryo or Three Kingdoms (37 BC-AD 668) period when excess heat from stoves were used to warm homes.
The continuing legacy of ondol
In the early 1900s, when the American architect Frank Lloyd Wright was building the Imperial Hotel in Japan, he was invited to the home of a Japanese nobleman. There Wright found a room that was different from typical Japanese rooms, with a warm floor covered with yellow paper—a Korean ondol room. The Japanese gentleman had experienced ondol in Korea and, once back in Japan, had an ondol room built in his house. “The indescribable comfort of being warmed from below” impressed Wright.
Wright decided then and there that ondol was the ideal heating system and began incorporating it in his buildings. Wright invented radiant floor heating, using hot water running through pipes instead of hot air through flues. In Korea, ondol has likewise been adapted to modern technologies and changes in fuel. Modern Korean homes and apartments are built with heating pipes embedded in floors that are typically concrete covered with vinyl or oiled papers. Heated water circulating through the pipes, warmed by a gas or oil boiler, has replaced heated air, minimizing the danger of carbon monoxide poisoning or burns.
With its modernization, ondol has received international recognition and has become increasingly popular abroad, particularly throughout Asia.
Modern underfloor heating systems are generally either warm water systems or electric systems. Systems can be poured into a masonry mix (called a poured floor system or a wet system) or fasteneddirectly to the sub floor (called a sub floor system or dry system). The Roman hypocausts (see below) used heated air.
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