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We explain central heating and tell you how to find out more


Central heating systems

Central heating is provided by one main heat source, or boiler, which then shares the heat it creates around the house. This is usually done by heating water, that is then piped to radiators, or underfloor heating systems. However sometimes the boiler heats air that is then fed through vents in each room.

Most central heating systems will also heat the domestic hot water, but it is possible to have a domestic water heating system that only heats the hot water and does not give central heating.

One of the most common forms of central heating is the Indirect Boiler System, which heats radiators and domestic hot water for the home using gas, oil, coal or wood as the fuel.

Indirect Boiler System
The indirect system is an efficient use of energy which heats water for both the heating system and the domestic hot water. This indirect system takes advantage of Thermal Dynamics – which is the technical term for heat rising. In this way warm water can continue to be drawn out of the top of the hot water tank, or cylinder, while cold water is fed into the bottom of the tank where it is warmed and rises to the top of the cylinder.

Domestic Hot Water
Cold water comes into the building from the mains, and is stored in a tank called a cold water storage tank (usually placed in the loft). The cold water is fed down from this tank, using gravity, into the bottom of the hot water cylinder. The flow of water into the hot water system is controlled by a ballcock valve in the cold water storage tank. When hot water is drawn off the hot water tank the pressure drops, this causes the ballcock valve to open in the cold water storage tank, and fill the hot water cylinder up from the bottom.

Water also comes from the cold water storage tank into the boiler, where it is heated and sent through the hot water tank in ‘spring shaped’ pipes, or coils. These are called Primary Flow and and Return Pipes. They form a loop inside the hot water cylinder, which allows the boiler-heated water to transfer its heat to the cold water in the hot water tank. When there is a demand for hot water it is drawn off the top of the cylinder, because this is where the water is warmest.

Space Heating or Room Heating
The boiler can also heat water in a loop of pipes that is pumped around the radiators (or underfloor heating pipes) in the house. Water is heated by the boiler and then pumped around the central heating system heating the radiators or under floor pipes. Then it returns to the boiler as it cools to be reheated by the boiler and sent back around the system. When the thermostat tells the system that the room temperature and/or water temperature is warm enough it signals the boiler to stop heating the water.

Once the temperature drops in the rooms, or the hot water cylinder, then the thermostat will signal the boiler to start heating, and the pump to start sending that hot water back around the system again.

If you want to read more about domestic hot water heating please visit our Domestic Hot Water Systems project page on our main site. This gives further information on direct and indirect boiler systems, stored hot water, unvented systems, thermal store systems, single and multi point water heaters, and combination or “combi” boilers.

If you want to know more about central heating boilers then can we suggest you visit our Central Heating Boilers project page.

There is also loads more about central heating on the main website – just go to our Project index page which lists all our projects alphabetically, and search for the subject you are interested in.

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