Tepidarium vs. Caldarium — What's the Difference?

The tepidarium was the warm (tepidus) bathroom of the Roman baths heated by a hypocaust or underfloor heating system. The speciality of a tepidarium is the pleasant feeling of constant radiant heat which directly affects the human body from the walls and floor.

A caldarium (also called a calidarium, cella caldaria or cella coctilium) was a room with a hot plunge bath, used in a Roman bath complex. This was a very hot and steamy room heated by a hypocaust, an underfloor heating system using tunnels with hot air, heated by a furnace tended by slaves.

(historical) A warm room in a Roman baths that was usually heated by a hypocaust.

In Roman baths, the hottest room, with a plunge-pool. It preceded the tepidarium and frigidarium.

(historical) A boiler in which the water was heated.

In modern spas, a room with a hot floor.

Any room containing a warm bath.