Roman central heating

To most people, their knowledge of the Romans was that they 'invented central heating.' Not the type we know today, but a form of underfloor heating that also warmed the walls. There were no such items as radiators in the Iron Age, but they did manage to use a form of heating that was radical for its day. Up until the Romans arrived, the British only knew how to heat one room by using a fire. The danger from such a method of heating was not only from the materials in their homes, but also from the smoke that could become trapped and suffocate the dwellers through smoke inhalation.

To understand how the Roman system of heating worked, take a look at the photo left which is from the Roman villa at Newport, Isle of Wight. Here you can see where the floor was laid out as series of concrete slabs raised up on tiles, with a furnace at the bottom of one exterior wall. By placing the fire here, the draught would take the heat under the floor, and up through the walls to chimneys located in the corners of the room. The height of the stack of tiles was about 2ft (60 cm) as this was found to be the most efficient height for the air to travel through.

Once the air had passed under the floor, the air was drawn into the walls and up the flues by the action of the hot air already rising in the flues creating a partial vacuum and so pulling the air below into the walls.

The walls were very often made of bricks with two holes horizontally through them. This had the effect of passing the air through the walls and into the flues, thereby warming the walls also.

In the Roman baths, the furnace was placed next to the hottest room caludarium in which three walls of this room were heated so that the room reached a temperature of up to 120 degrees F (50 degrees C). The warm room tepidarium only had one wall heated which made this room cooler than the caludarium.

The heating system was a labour intensive device as it required constant attention to feed the fire and remove the ashes. As such it was the wealthy and those with influence that could afford to have it.

The furnace was the heating source of the system and this was placed on the outside of the house, below the floor that ran under the room that was to be the hottest room in the house. One room was always hotter than he rest, as the air flowing under the floor would naturally lose some of its heat as it was traveling under the floor.

The fire would need regular attention from a slave, or one of the household workers who would have to rake out the ashes with a long handled tool and use the same tool to push new fuel into the fire. The fuel was mainly small branches and twigs up to about 3 inches in diameter and up to two feet long which was placed 2-3 feet into the furnace opening. This was allow the air to be drawn in and around the wood and so make sure the air flowed freely. Logs were not used as these burned too slowly to be effective and too many would block the passage of air. The height of the fire was restricted to around half the height of the opening so that air could flow through the flames and so increase the heat output. This was essential in the baths were the maximum amount of heat had to be generated.