How central heating works
A good central heating system provides heat and hot water as and when they are needed, This chapter looks at wet (radiator) heating. The following chapter covers electric storage heating and gas-powered and plug-in fires.
A typical wet (radiator) system can be timed to come on early in the morning for the rush to work and school, go off during the day, then warm up again in the early evening. Modern, sophisticated controls add to the efficiency of the system, allowing different settings for each day and varying heat levels.
Less popular forms of central heating are warm air and underfloor systems. Because they are complicated to fit, they are mainly installed only in new buildings. In a warm air system, a fan draws air across a heater then circulates warmth via ducts hidden in the walls. The heated air enters the rooms through grilles. Underfloor heating comes from cables, set into either the floor or ceiling. It is slow to heat up and cool down. Both of these systems are slow to heat up and cool down, difficult to control and quite expensive to run.
A wet central heating system has four main parts: the boiler, the radiators (or other heaters), the connecting pipework and tanks and the controls. The boiler Fuelled by gas, oil, solid fuel or electricity, the boiler heats water which is circulated by a pump through pipes and radiators.
The type of boiler and its heating capacity should be worked out bearing in mind the size of the house, the amount of heat loss from rooms, the amount of hot water needed and the number and size of radiators required, Boiler size is measured in kilowatts (kW). Working out the size of boiler is best tackled by a qualified central heating engineer. Boiler on and off times are controlled by a programmer. Pipework Most central heating systems connect to radiators through copper piping. Thin, flexible piping, known as microbore, is unobtrusive. The pump Hot water is circulated around the system by an electrically-operated pump, usually situated near the boiler. In most systems, there are two tanks – the hot water cylinder, which provides hot water to the hot taps in the house and a feed-and-expansion tank. The feed and expansion tank has two sections – one to hold cold water to top up the system and the other to contain overspill from the system as the water heats and expands. The feed-and-expansion tank is usualy situated in a loft.
