Boiler Efficiency Ratings

Compare new boilers and assess whether your current boiler would be better off being replaced

Our boiler efficiency tables provided by SEDBUK (the seasonal efficiency of domestic boilers in the UK) provide a guide of how effective your boiler is at turning fuel into heat.

You can check your boilers rating by selecting it’s make and model below. Ratings are based on the SEDBUK Rating which is an indicator of its efficiency when used within an average domestic household, it’s a great benchmark for comparing new boilers and also assessing whether your current boiler would be better off being replaced due to low efficiencies.

For new boiler installations call British Gas Boilers on 0333 230 5216 for a no-obligation quote, alternatively visit Boiler Guide to request quotes from independent local and regional heating engineers.



RSF 21 E/3S Efficiency

SAP seasonal efficiency


Rating band

Band D


ManufacturerRadiant Boilers
ModelRSF 21 E/3S
Fuel TypeGas
Flue TypeRoom-Sealed
FanFan Assisted
Output (kW)26.6 - 26.6
Boiler IDCE 0694BL3003
Manufactured From/To2000 - current


The Radiant RSF 21 E/3S is a 'D' rated boiler with an efficiency of 80.3%.

The RSF 21 E/3S is a Non-Condensing Combi boiler with a maximum power output of 26.6kw that uses Gas as its fuel source.

Being a 'D' rated boiler it would be worthwhile replacing it with a higher efficiency 'A' rated boiler.


Similar Radiant Boilers to the RSF 21 E/3S
(Non-Condensing Gas Combi)

Results ordered by efficiency. Some models may be obsolete.

Radiant RBA CS 30/100

81.1% Efficient

Radiant RMAS 21 E/3S

80.9% Efficient

Radiant RBA CS 30

80.8% Efficient

Radiant RMAS 30 E

80.7% Efficient

Most Efficient Combi Gas Boilers

Alpha CD50

91.2% Efficient