With central heating, the heat is generated in one central place which is considered the furnace or boiler by energy sources such as electricity, gas, oil or solar energy and then distributed throughout the home or building. There are two means for this, "forced air" or "forced water". With forced air the air is warmed by the energy source and then transported through duct work to all the rooms. With forced water the water is warmed by the energy source and then the water flows through pipes into radiators in each room which emit heat. The amount of heat is controlled by using a thermostat which regulates the temperature of the home or building..