The hypocaust heating system

Roman central heating
In any list of Roman achievements, the invention of central heating usually comes somewhere near the top. Although the Romans were not the first to develop underfloor heating systems (examples have been found in the remains of a number of earlier civilisations), they did spread the idea far more widely than previously, warming the feet of citizens throughout the empire with their hypocaust heating systems. This ingenious heating system was at first a status symbol of the rich and wealthy, but later became a standard design in many public facilities and prominent houses.

At Whitestaunton, Time Team decided to recreate a hypocaust for the reconstruction cameo. 'Before we came to this site we knew that some bits of box tile flue had been found and that gave us some pointers,' says Melisa Akdogan, the cameo producer. We decided to build a reconstruction of a hypocaust system so that we could show how these things were engineered. I'm really pleased that the project has worked. Three days is not very long for this type of building project but we've had some good builders and Bob Swain, our engineer, has been brilliant. The local suppliers have also been very good to us.'

Bob the builder
Fire technology expert Dr Bob Swain has studied hypocaust systems for years and understands how they should be built. 'The basic system is fairly simple really,' says Bob. 'You have a floor that is suspended on pillars made of layered terracotta tile about 2 feet (60cm) high. This creates a hollow void underground. Leading into this is a furnace at fairly low level which burns wood to create the heat. The underground void also has flues at regular spaces which are built into the walls to channel the heat throughout the system. The result is a nice hot floor and walls in whichever structure the system is based.'

By tapping the tops of the flues it is possible to draw the heat to different areas of the floor and from this Bob deduced that a relatively small furnace could be used to heat several large rooms. Another interesting feature of the experiment is that it was found that constant stoking of the furnace wasn't necessary. After the stonework had reached the right temperature, it just needed to be kept ticking over.

A good burn
Bob continues: 'You can imagine that the stoker would have had to get a good burn going to get the stone nicely heated. They would then need to dampen down various flues to circulate the heat properly, a bit like playing a tune. However, the stone holds the heat very well, so after the building was comfortable they could sit back a bit, just stoking when necessary. This way a room could still be warm in the morning after it had been left all night.'

By the end of Day Three most of the Team had taken off their boots and socks and enjoyed the cosy feeling of walking around on the Roman technological wonder.

See also How to build your own hypocaust

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