The use of water as the heat move medium is known as hydronics. The system also contains either ductwork, for forced air systems, or steaming to distribute a warmed fluid and radiators to transfer this heat to the atmosphere. There are many different types of standard heating systems. Central heating is often used in cold climates to heat private houses and open public buildings. Such a system includes a boiler, furnace, or electric to heat water, vapor, or air, all in a central location such as a furnace space in a home or a mechanical room in a large building. The term radiator in this context is misleading since most warmth transfer from the heat exchanger is as simple as convection, not radiation. The radiators might be mounted on walls or hidden in the floor to give under-floor warmth.
In boiler fed or radiant heating systems, basically the simplest systems have a pump to circulate the water and ensure an equal supply of heat to all the radiators. The heated water may also be fed through another (supplementary) heat exchanger inside a storage tube to provide hot running drinking water.
Forced air systems send heated air through ductwork. Throughout warm weather the same ductwork may be used for air conditioning. The pressured air can also be filtered or put through air cleaners.
Heating can also be provided from electric, or resistance heating using a filament that becomes hot when electric current is caused to feed it. This type of heat can be found in electric baseboard heaters, portable electric heaters, and as backup or supplemental heating with regard to heat pump (or reverse heating) system.
The heating components (radiators or vents) should be found in the coldest part of the room, usually next to the windows to minimize condensation and offset the convective air current formed in the room due to the air next to the window getting negatively buoyant due to the cold cup. Devices that direct vents away from windows to prevent “wasted” warmth defeat this design intention. Cold air drafts can contribute significantly to subjectively sensation colder than the average space temperature. Therefore, it is important to control the air leaks from outside along with proper design of the heating system.
The invention of central heating is often credited to the ancient Romans, who installed a system of air ducts called a hypocaust within the walls and floors of public baths and private villas.