Rome's hypocaust heating

In wealthy homes and public bathhouses of ancient Rome, builders used the hypocaust, a form of underfloor heating. A raised floor rested on brick pillars, allowing hot air from a furnace to circulate beneath it; in some buildings, it also rose through channels in the walls. The system required a maintained fire and a steady fuel supply. It was an advanced way to heat rooms for its time, but it was neither inexpensive nor efficient by modern standards.