Underfloor
Underfloor heating uses a network of pipes, tubing or heating cables is buried in or attached beneath a floor to allow heat to rise into the room. Best results are had with conductive flooring materials such as tile. The large surface area of such room-sized radiators allows them to be kept just a few degrees above desired room temperature, minimizing convection. Underfloor heating is more expensive in new construction than less efficient systems. It also is generally difficult to retrofit into existing buildings.
The Roman hypocaust employed a similar principle of operation.
Read more about this topic: Radiator (heating), Types