Last edited 15 Nov 2025

Seasonal Efficiency of Domestic Boilers UK SEDBUK

Seasonal Efficiency of Domestic Boilers (SEDBUK) is a rating system that is used to measure and compare the energy efficiency of boiler systems in the UK. It was effectively superseded as the accepted efficiency labelling system by Energy-related Product (ErP) assessments when the EU Ecodesign Directive was introduced. ErP assessments cover similar issues but across a broader EU range of products, setting minimum performance standards, and establishing the ErP compliant labelling system. SEDBUK may still be given on some products, along with an ErP rating because it has a higher level of granularity giving percentage performance as opposed to letter grading under the EU Ecodesign Directive. .

The initial SEDBUK rating system was introduced in 1999 and had two iterations, SEDBUK 2005 which used a letter rating system from A (most efficient) to G (least efficient), similar to the EU ErP system, then 2009 this was changed to give a higher percentage score for better performance (SEDBUK 2009) which was deemed to be more accurate than the first version. SEDBUK assessments measured the efficiency of a specific boiler system when performing over an entire heating season, as opposed to under ideal conditions by measuring energy losses during standby mode, boiler cycling losses, as well as heat losses through the flue.

The ErP (Energy-related Products) directive, which was introduced in 2015 under the EU Ecodesign Directive uses a letter rating (A+++ to G) for a broader range of energy-related products across the whole of Europe. Whist the requirement for products to adhere to the ErP and EU Ecodesign Directive applied to all UK products, SEDBUK ratings were often still used because of their percentage outcomes and continued use for the UK Standard Assessment Procedure (SAP). Many of the EU Ecodesign measures were transposed into UK law before the end of the Brexit transition period, because market ties with the EU remained close even after Brexit. SEDBUK ratings are still used in specific contexts, such as for SAP (Standard Assessment Procedure) calculations for new build homes.

The Product Characteristics Database (PCDB) is a support tool which used for the Standard Assessment Procedure (SAP) along with SAP Appendix Q database, both are provide by the BRE. Both list the performance data for a wide range of different products which includes boilers, aswell as heat pumps, mechanical ventilation, micro CHPs, Flue gas recovery systems, waste water recovery systems, compensating boiler controls and Time and Temperature Zone Control, high heat retention storage units, community heat networks and heat interface units.

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