Hydronic Heat
There are three main components in any given hydronic heat system.
First and most importantly - there is the heat source. This is used to heat the water in the system. Boilers and hot water heaters are most common, but heat pumps and even solar panels can be used to supply heat to a radiant system.
Secondly, there has to be some kind of control system. This would include items like pumps, valves, fittings and adapters. Essentially, you need a way to control the distribution of the heated water to the various zones. A thermostat sends a signal calling for heat. This can open a valve or valves and/or turn a pump on - sending hot water to the zone that is calling for heat.
Third, you need a piping to distribute that heat - a distribution system. A competent radiant designer can draw up a customized tubing layout plan. When followed, this tubing will become the means by which heat is transfered from the heat source into your home.
Typically, a thermostat will call for heat in a given zone. This will cause a valve or valves to open and a pump will begin circulating hot water to the piping in that zone. The piping will transfer heat into the floor, gently warming the room. Once the thermostat is satisfied, the valves will close and the pump will shut off.
The heat source can be powered by natural gas, electricity, oil, propane - sometimes wood or even solar. For more information about hydronic heat and proper
radiant design <- just follow that link.