A central heating boiler is a closed vessel or appliance that heats water (or, less commonly, generates steam) for distribution through a network of pipes and emitters to provide space heating and domestic hot water throughout a building. It is the core component of most central heating systems in residential and commercial buildings.
Applications
Central heating boilers are among the most common building services installations in temperate and cold climates. They work by burning a fuel (natural gas, oil, LPG, or biomass) or by using electricity to heat water, which is then circulated through the building via pipes to radiators, underfloor heating loops, or convectors. The same boiler often also heats domestic hot water for taps and showers, either directly or through a separate hot water cylinder.
Modern boilers are categorized into several types based on their operating principle. Combi (combination) boilers heat water on demand for both space heating and domestic hot water, without the need for a separate storage tank. System boilers work with an external hot water cylinder, providing stored hot water at mains pressure. Regular (conventional) boilers require both a hot water cylinder and a cold water storage tank, and are typically found in older installations.
Condensing technology has become the standard in most countries. Condensing boilers recover heat from the exhaust flue gases by cooling them until the water vapor they contain condenses, releasing additional energy. This makes condensing boilers significantly more efficient than older non-condensing models, with typical efficiencies above 90 percent.
The choice and sizing of a boiler depends on the building’s heat demand, which is determined by factors such as floor area, insulation levels, climate, and the number of occupants. Proper installation, including correct flue routing, system design, and controls (thermostats, timers, zone valves), is essential for safe and efficient operation.
As the construction industry moves toward decarbonization, heat pumps are increasingly replacing boilers in new buildings, though boilers remain the dominant heating technology in the existing building stock.
Related terms
- Radiator
- Underfloor heating
- Heat pump
- Condensing boiler
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