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SEDBUK Rating and Condensing - what do they mean?

Sedbuk.jpg SEDBUK is an acronym for 'Seasonal Efficiency of a Domestic Boiler in the UK'. The system was developed under the UK Government's energy efficiency best practice programme with the co-operation of boiler manufacturers and provides a basis for fair comparison of different models of boilers.

The SEDBUK rating is the average annual efficiency achieved in typical domestic situations, making sensible assumptions about climate, control, pattern of usage and other similar factors. The rating is calculated from laboratory tests together with other important factors such as boiler type, fuel used, ignition type, UK climate, boiler water content and typical domestic usage patterns. For estimating annual fuel running costs SEDBUK is a better guide than laboratory test results alone.


To establish the foundation calculations for SEDBUK test work took place over three years during which a theoretical seasonal efficiency model was developed. Experimental data was obtained from over 20 different boilers, supported by data collected from field trials in 99 homes to support these theoretical assumptions. This allowed fuel usage data (termed 'signature') to be related to efficiency test results supplied by manufacturers.

The boiler's performance is then scored which enables the boiler to be placed in a banding system using a scale from "A" to "G." "A" banded boilers being the most efficient and usually termed 'condensing' boilers.


The term 'condensing' is derived from the creation of condensation within the heat exchanger or flue. This liquid will need to be conveyed away to a drain via a plastic discharge pipe run by the installing engineer. When combustion of any kind takes place water vapour is always produced. In a 'standard efficiency' boiler the flue gas temperature is kept relatively high to avoid condensation and its related issues. But in a high efficiency boiler, so much of the heat produced in the combustion process is absorbed by the heat exchanger into the heating water and very little is wasted to the atmosphere via the flue, hence less fuel is burned to achieve the same results but the consequence is condensation which is dealt with in the appropriate manner.



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