Older than you think!
Once very unusual in the UK, underfloor heating in now commonplace, particularly in new builds. However, it was first used by the Romans - the picture on the left is an example from Hadrian's wall. They used stone pillars with slabs to create gaps through which warm air was circulated, heating the room above.
So how does Underfloor Heating work?
Today's underfloor heating systems use plastic pipes embedded within the floor make-up. Low temperature water is circulated through the pipes which in turn gives off heat to the floor, warming the room.
Each room will have one or more circuits of pipe depending on it's size. These circuits are connected back to a central manifold, with each circuit of pipe controlled individually to give the level of control required. A typical underfloor heating system will allow for separate temperature control in each room using individual room thermostats, which control the flow of water using thermal actuators, which are connected to each circuit of pipe.