This term refers to any type of ‘wet’ heating system (wetted due to the circulation of water), whether it is a gas boiler, oil boiler, electric boiler, or an energy source such as a heat pump or biomass boiler. Therefore, electric heaters and gas fires are not classified as central heating systems.

A central heating system consists of a boiler (oil, gas, electric, biomass, or heat pump), radiators or underfloor heating, pipework, and heating controls. Pumps are used for all central heating systems, either directly on the boiler or outside the boiler.

Heating the water and pumping it around radiators and/or underfloor heating pipes in the home is done by a boiler or heat pump. A thermostat (also referred to as a heating control) initiates the boiler/heat pump’s operation and keeps it running until the desired temperature is reached.

The boiler may operate differently depending on how the system is set up for on/off and continuous heating. A heating system’s efficiency can be greatly impacted by this.

A central heating system was originally open-ventilated, which meant air could escape at the top point, usually in the loft. Most systems today are ‘sealed’, which means air cannot escape on an ongoing basis, so air first must be removed from it. Nowadays most boilers are for sealed systems, but some are available for open venting (OV). Read our Guide to open vented and sealed systems first if you have an open vented system and are considering changing it.

A condensing boiler is more efficient than a traditional boiler. In the home, efficiency drops from 92-94% on-the-box to closer to 80% without condensing. In order to maximize efficiency, condensing gas or oil boilers should run at a lower temperature for a longer period of time.

Condensing does not occur in electric boilers or most biomass boilers. There is no need for a flue on an electric boiler, and a chimney is used instead of a flue on a biomass boiler. As such, electric and biomass heating systems can run at higher temperatures; however, there could be a concern about increased wear and tear if the boiler switches on and off all the time rather than running at a lower output for a longer period.

How does balancing work? The key to the efficient use of older gas and oil boilers, as well as heat pumps, electric boilers, and biomass boilers is to ensure that all the radiators are heated. Unless it is made to go around all of the radiators, water will just follow the route of least resistance.

Radiators should be restricted from being accessed near the boiler (using thermostatic radiator valves or TRVs) and allowed free access farther away in order to balance the system. So, the hot water is circulated throughout the whole system. There are many types of Radiator valves.