Ancient Rome heated some floors with air from underground furnaces beneath the rooms.

The longer version

Rooms were raised on short pillars of brick or stone, leaving a hollow space beneath the floor. A furnace fed hot air and smoke into that cavity, and the warmth rose through the floor slabs and up flues built into the walls, so the room heated from the ground and the walls at once.

Such systems burned large amounts of fuel and needed constant attention, so they appeared mainly in bathhouses and the richer rooms of villas. Tiles and mortar conducted and stored heat well, which meant the temperature stayed fairly even long after the fire died down.

Where this entry sits

This set looks at ancient civilizations, old inventions, trade routes, calendars, and the ordinary objects people once used every day. Nothing here is advice or opinion, just short notes about how daily life used to be organised long ago. The full list sits on the History page, where every entry is listed in order.