A commercial boiler is a pressurised system that burns combustible fuel to heat water. Some types of boiler distribute the hot water itself, whilst others use water that has been turned into steam. The hot water or steam is circulated via pipes and enters the radiators or other types of heater you have throughout your commercial property, keeping the spaces warm and comfortable for staff, clients or customers.

Natural gas is the fuel most commonly used within commercial boilers, though other types of boilers that burn fuel oil or bio-fuel, or produce heat using electric coils are available. In this article we’ll take a closer look at the main components that make up a commercial boiler.


The burner is the part of the boiler where air mixes with the fuel source and combusts. The hot combustion gases then enter the boiler, which serves as a heat exchanger. The right amount of combustion air is important for a clean and efficient combustion, so this is a component of your boiler that needs to be kept in good working order. Too little air won’t allow for complete combustion, whereas too much will allow for excess loss of exhaust gases.

Combustion Chamber

The combustion chamber is the component of the boiler where the fuel is burned to heat the water. The chamber contains the burners and is designed to provide a very safe area for high-temperature combustion of volatile fuel. It is usually made of steel or cast iron, or another heavy duty metal that can cope with temperatures reaching several hundred degrees. This is another part of the boiler that needs to be serviced on a regular basis, as older units can become corroded or cracked, which makes them unsafe.

Heat Exchanger

The heat exchanger is the component that transfers the heat produced by the burners within the combustion chamber to the water in the boiler. Heat exchangers can be made up of a variety of elements, including bundles of steel tubes, cast iron or copper lines. The elements need to be made of very sturdy material that is able to withstand high temperatures, last a long time and transfer heat efficiently.


The system controls allow the user to set water temperature, air and fuel supply mixtures, internal pressure and ignition. The controls regulate how often the burner fires, the quality of the mixture of fuel and oxygen, the rate at which the fuel is used, and how hot the water gets. The controls are also an important part of the safety system of your boiler.

Uncontrolled, high-pressure steam can be incredibly dangerous, and well-maintained system controls help to keep your boiler completely safe by making sure that the internal pressures within it don’t go too high, the water stays within a safe temperature range and the system continues to operate properly.

Supply Lines and Return Lines

Supply lines lead from the boiler and deliver the heated water or steam to distribution points around your building, such as radiators or heaters. When the water out at these points cools, or the steam cools and changes back to water, the return lines bring the water back to the boiler where it is reheated before being sent out again.

Circulator Pump

The circulator pump is the component that pushes the hot water out through the supply lines to the radiators or other distribution lines. It is also responsible for bringing it back through the return lines. The circulation pump plays a crucial role in the functioning of your boiler and must be well maintained to ensure the system is working as efficiently as possible.

Exhaust Stack

The exhaust stack – sometimes known as the chimney or flue – is designed to safely expel spent fuel away from the building’s exterior. An exhaust stack may look like a traditional brick built chimney, or it might be a series of metal pipes. The exhaust stack must be safely constructed so that dangerous gases such as carbon monoxide are diverted away from the interior of your property, as well as making sure it isn’t expelled near windows and doors. It’s also important that they are not constructed in such a way that could allow downdrafts of powerful winds to re-enter your commercial property.


The best way to keep your commercial boiler working as efficiently, and therefore as cheaply, as possible is to have it maintained on a regular basis. There are many components that need to be checked over by a qualified inspector to ensure they are in good condition and will not break down. It’s important to remember that boilers are volatile systems containing high pressure steam and very hot water, so it’s vital to make sure every element is clean and working properly, and that all safety systems are functional.