Condensing Boilers

A Condensing type boiler is one that can have an increased efficiency over the more traditional boiler. The efficiency of a typical non-condensing boiler is around 75%, whereas with condensing boilers it can be over 87%.

The increased efficiency of a condensing type boiler is due to the extraction of heat from the otherwise wasted flue gases. Most boilers have a single combustion chamber enclosed by the waterways of the heat exchanger through which the hot gases can pass. These gases are eventually expelled through the flue, located at the top of the boiler, at high temperatures.

Condensing boilers allow the heat to pass through the primary heat exchanger and the gases are then passed over a secondary heat exchanger. During this process, this process reduces the flue gases to about 55°C. The reduction in temperature causes the water vapour to condense and collect, hence a condensing type boiler. The remaining gases are expelled to the outside environment through a fan-assisted balanced flue.

Although SEDBUK is expressed as a percentage, an A to G scale of percentage bands was also in use until October 2010. This has been withdrawn to avoid confusion with the proposed European energy label using similar ratings based on different principles.