Hypocaust, heating of the rooms

The hypocaust was a type of central heating used in ancient Rome that used the circulation of hot air, produced in the praefurnium (a large furnace fired up by slaves), inside empty spaces specifically constructed in the floor or walls of the rooms to be heated.
The floors were called suspensurae because they were suspended on brick pillars that allowed heat to circulate underneath. It was possible to control the temperature of the rooms by adjusting the power of the fire, while special pipes removed the smoke.