Hypocaust System

The ancient Roman hypocaust system

The hypocaust system (hypocaustum in Latin) was a heating system used in (wealthy) Roman houses and Roman baths, and the closest thing to central heating today. The hypocaust was a system that circulated hot air under the floor and surrounding walls. A furnace would heat the air. The floor was raised above the ground by pillars that were called pilae, so that hot air could circulate under it. There were also flues under the walls that circulated the hot air which escaped from the roof.

The floor consisted of a layer of tiles then a layer of concrete and then another layer of tiles. The walls had ceramic tiles in them in order to maintain the heat. The Romans made sure that the hot air and smokes didn't leak from the floor and the walls which was quite a feat of engineering considering the materials used at the time. A leaking floor was very dangerous and could even cause death as CO2 is odorless and toxic.

Rooms that required the most heat were placed close the furnace. For the baths this room was called the caldarium. The heat could be increased by adding more wood. It is worth noting that operating a hypocaust was quite expensive. It required labor and wood to maintain the fire. Labor usually consisted of slaves that would monitor the fire.

Only wealthy Romans could afford to have such a system in their home! Firstly, building a hypocaust was expensive and required skilled engineering. Secondly, it required slave labor to fuel and monitor the furnace for hours. Thirdly, there were probably maintenance and repair costs which were also expensive. But it is worth noting that most Romans could experience the joys of such a heating system by visiting the thermae or the Roman hot baths where walls and floors were heated. The Pompeii Old Baths is a good example of such public baths.

Interesting facts about the hypocaust system
  • The word hypocaust comes from the Greek words "hypo" which means "under" and "caust" which means "burnt".
  • After the demise of the Western Roman Empire, central heating in homes in Western Europe did not exist until the 20th century!
  • Historians have tried to build hypocausts using the Romans' materials and techniques and have found it very difficult to build walls that did not leak.
  • The hypocaust was invented by a man named Sergius Orata.

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