Debunking boiler buzzwords

Steven Evans explains the boiler jargon

School facilities managers work closely with heating engineers to ensure heating systems are maintained. But when the boiler jargon comes out, it can seem like they are speaking another language – which is frustrating on both sides. To cut through the tech talk, Potterton Commercial’s national sales manager, Steven Evans, has compiled a glossary of some commonly used terms.  

Heat exchanger

The heat exchanger is one of the most important components in a boiler. It consists of a series of coiled pipework containing water or a cast block of aluminium with water passing through it. The heat exchanger is designed to pick up the maximum amount of heat. When the boiler burns gas, it generates heat as a product of combustion. This is then passed over the heat exchanger and the thermal energy is transferred to the water, which is then circulated around the system.


Condensing boilers are one of the greatest innovations of recent years. They are much more efficient and produce lower levels of carbon dioxide than non-condensing models, making them cheaper to run and better for the environment.

With a non-condensing boiler, the warm waste gases travel through the boiler’s flue and escape into the outside atmosphere, taking valuable heat with them. However, in a condensing boiler, the heat that would have otherwise been lost are recovered and recycled to warm up the cool water that returns from the radiators as it enters the boiler. The gases travel through a heat exchanger during this process, which cools and condenses them back into a liquid known as condensate (hence the name).


When discussing the lifetime cost of a boiler, a heating engineer may mention its modulation capabilities. But what does this mean? In simple terms, a boiler’s modulation range is the difference between its maximum and minimum output, generally expressed as a ratio. As an example, Potterton Commercial’s Sirius two boilers have a modulation ratio of 9:1, which means that the 90kW model can modulate down to 10kW. In general, the wider the ratio, the better as it offers more flexibility to meet fluctuating heat demand, and prevents the boiler from constantly turning on and off which can damage the parts.


A cascade is an arrangement of two or more linked boilers in the same heating system. This increases the overall output without compromising on efficiency, as individual boilers can be turned on/off according to demand. Rather than installing one 400kW boiler, a contractor may choose to cascade four 100kW boilers to provide the same output but with greater flexibility.

Weather compensation

Weather compensation is a piece of technology that monitors the outdoor temperature via a sensor and modulates the boiler output accordingly. This is because when it is mild outside, the room temperature is likely to be close to the set point already, so less power is needed to achieve the desired temperature.

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