Well, it is thought that the early Greeks were the first to develop such a system but it was the Romans who put it to practical use with their hypocaust system. In many Roman buildings, mosaic tile floors were supported by columns below, which created air spaces, or ducts. At a site central to all the rooms to be heated, charcoal, brushwood and in Britain, coal were burned and the hot gases traveled beneath the floors, warming them in the process. The hypocaust system disappeared with the decline of the Roman Empire and "central heating" was not reintroduced until some 1,500 years later. The Romans were not alone in their development however, the ancient Koreans had their own system of floor heating. With temperatures in winter dropping to as far as 20 degrees below zero there was obviously a great deal to be gained by developing a system to keep warm. Since the 5th century they have built their homes with an "ondol" (which translates as "warm stone") floor. While similar to the Roman hypocaust system the ondol relies on warm water. This system is used in Korea to this day! More..