Gas boilers in the UK are rated under the EU Energy-related Products (ErP) Directive, displayed as a colour-coded scale from A++ (most efficient) to G (least efficient). Here's what it all means.
The ErP rating scale
- A++ or A+: 94%+ efficiency — top-tier modern condensing boilers
- A: 90–94% efficiency — most modern condensing boilers
- B: 86–90% efficiency — older or budget condensing boilers
- C–G: Below 86% — older non-condensing boilers (pre-2005)
What SEDBUK was
Before ErP, UK boilers used the SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) rating, also expressed as A–G. Most people still refer to boiler efficiency as "A-rated" — meaning 90%+ efficiency. The ErP and SEDBUK A-bands broadly overlap.
How much does efficiency matter?
The difference between an A-rated (92%) and A++ rated (96%) boiler is relatively small in annual savings — around £60–£80/year. The bigger efficiency gains come from replacing old G-rated boilers (70–75% efficiency) with any modern A-rated boiler.
Seasonal efficiency vs test efficiency
Real-world efficiency is always slightly lower than the lab rating because condensing boilers only achieve maximum efficiency at low-return water temperatures. Modern weather-compensation controls can help get closer to the rated efficiency in real conditions.