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.



S2 70/90 Efficiency

SAP seasonal efficiency


Rating band

Band C


ManufacturerMistral Boilers
ModelS2 70/90
Fuel TypeOil
Flue TypeOpen or Room-Sealed
FanFan Assisted
Output (kW)20.5 - 26.4
Boiler ID
Manufactured From/To2006 - current


The Mistral S2 70/90 is a 'C' rated boiler with an efficiency of 85.7%.

The S2 70/90 is a Non-Condensing Conventional boiler with a maximum power output of 26.4kw that uses Oil as its fuel source.

Although a 'C' rated boiler is not as efficient as many other modern boilers it's still pretty good, only a marginal reduction in fuel bills and carbon dioxide emissions would be observed by replacing it.


Similar Mistral Boilers to the S2 70/90
(Non-Condensing Oil Conventional)

Results ordered by efficiency. Some models may be obsolete.

Mistral KUT4 120/150

85.7% Efficient

Mistral KUT3 90/120

85.7% Efficient

Mistral BH3 90/120

85.7% Efficient

Most Efficient Conventional Oil Boilers

Grant Vortex 36

97.0% Efficient