Image by USACE Europe District
Central heating systems provide warmth to an entire building or at least a portion of the building. The heating system by itself can be combined with ventilation and air conditioning systems to be jointly called a HVAC system. In the central heating system, the heating is done at a single or centralized location. This heat generation is usually done by burning a fossil fuel. The heat thus generated then gets distributed. The heat moves through ducts carrying forced air. Sometimes, heated water or even steam is circulated through the pipes.
Most modern houses in regions where the climate is not temperate in nature have built-in central heating systems. Even such houses use oil or gas to heat the boilers. Electrically heated systems are not very common. The fossil fuel heating systems heat space more efficiently than when there is combined electrical and fossil fuel heating systems in place in the home.
When water circulation is used for central heating systems, the boiler heats the water in a closed system. A pump is required to circulate the water in the closed system. There are also radiators that actually radiate the heat into the rooms. These are usually mounted on the walls of the rooms. This heated water is also used to heat water stored in a tank, through a heat exchanger system, to provide hot water for the purpose of washing, to flow out of taps for various domestic uses, and to service washing machines, etc.
Electric heating converts electricity to heat directly. The principle used is that of resistance heating. It is more expensive to produce heating in this method compared to that produced by combustion of fossil fuels. Heat generated by electrical resistance heating can be wall heaters, radiator heaters, etc.
Central heating systems work more efficiently when many rooms of a large building or house need to be heated. It is not efficient to heat a single room in isolation, as most of the heat is lost. In such cases, individual heaters would function much better.
District heating is a system that distributes heat generated from a centralized location. Here the heat is generated from a co-generation plant and they provide higher efficiencies and better pollution control than the conventional local boilers. A co-generation plant uses a heat engine or a power station to simultaneously generate electricity and useful heat. It is being increasingly used in the Scandinavian countries.