Caius Sergius Orata is credited, by Vitruvius, with inventing the hypocaust. The word, from the Latin hypocaustum, in a literal translation, means access from below. The hypocaust is a raised floor system on ceramic piles where, at one end, a furnace—where firewood is burned uninterruptedly—provides heat to the underground space, which rises through walls constructed of perforated bricks. Hypocausts heated, through the floor, some of the most opulent buildings of the Roman Empire (including some residences) and, above all, the famous Public Baths.
With a similar function, but in the East, there existed the ondol. It is estimated that it was developed during the Three Kingdoms of Korea (57 BC-668 AD), but researchers point out that the solution was used long before that. The system also manipulated the flow of smoke from agungi (rudimentary wood stoves), rather than trying to use fire as a direct heat source like most heating systems. It even caught the attention of Frank Lloyd Wright, as pointed out in this article, who adapted the system to use it in heating homes in the United States and in his important Imperial Hotel in Tokyo. How do radiant floor heating systems currently work?