These boiler ratings are called SEDBUK – Seasonal Efficiency of Domestic Boilers in the UK.
There are two SEDBUK boiler ratings systems, SEDBUK 2005 and the newly updated SEDBUK 2009. SEDBUK 2005 uses an A to G rating, A-rated boilers being more than 90% efficient. SEDBUK 2009 no longer uses the A-G rating but only displays the percentage efficiency.Under the new system a SEDBUK 2005 90% efficient A-rated boiler will be regarded as 88% efficient, according to SEDBUK 2009. This goes for gas, oil and LGP boilers. The 2% difference between SEDBUK 2005 and 2009 is mainly down to differences in efficiencies between using a boiler for space heating in the winter months and only using it for water heating in the summer months.
The A to G rating will still apply if the boiler was tested under SEDBUK 2005, and should be made clear under what test standards the boiler was tested.New minimum efficiencies for gas, oil & LPG replacement boilers in Great Britain.