How does central heating work

asks paulmac

A. Wel,l to make things complicated there are various types of system. In the UK, most households use a hot water system.

In a hot water system, a boiler heats water and circulates it through pipes. The pipes supply radiators with hot water and return the cool water to the boiler. Water is pumped through the pipes using a circulator.

In some older central heating systems water is circulated through the radiators by gravity rather than by a pump. When the water is heated it expands becoming less dense and lighter than cold water. The cold water sinks down the return pipe forcing the lighter hot water up the flow pipe and around the radiators.

Q. Does the water from the hot tap come from the radiators

A. No, they're two separate systems.

Q. How is the temperature and time controlled

A. The boiler is switched on automatically at chosen times using a programmer.

Temperature is controlled using a thermostatic control, known as a 'roomstat'. The roomstat is placed in a room, which typically has a relatively stable temperature, for example the living room, where it monitors any change in temperature. The roomstat then maintains the temperature at a set level by switching on or off a pump or motorised valve, which allows water heated by the boiler to flow through pipes to the radiators.

The same water flows around the system until the desired temperature is reached after which the roomstat shuts down the pump or valve.

Q. What other types of central heating system are there

A. The other main type is called 'forced air' heating.

Q. How does forced air heating work

A. This system uses ducts and an air blower to circulate warm air. The blower pushes the air through the ducts into the rooms. The cooled air is then pulled back to the furnace through return ducts, warmed again, and then returned to the room once more.

An advantage of a forced air system is that a central air conditioning system can be attached.

Q. How are central heating systems powered

A. In the UK, usually by a boiler running on either gas or oil. Other sources of power include furnaces, using gas, oil or electric and electric heat pumps.

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by Lisa Cardy