in korea, radiant underfloor heating has been in use for about 2000 years. ondol, which means "warm stone," involves the use of stones and underground ducts to help transport warm air from the kitchen to the rooms in the house. most homes and buildings in korea still use ondol, although they now use hot water and electric systems. the american architect frank lloyd wright discovered ondol in the early 1900s and used it in many of his building designs. wright also invented hot water underfloor systems.