How to Check Boiler Efficiency Ratings

Boiler efficiency is expressed as a percentage — how much of the gas burned is converted to useful heat. Here's how to find and compare these figures.

Where to find efficiency ratings

Two main sources:

1. The ErP energy label: Displayed on all new boilers. The letter grade (A++ to G) and the percentage figure below it are the seasonal space heating efficiency.
2. The PCDB (Product Characteristics Database): The official UK database at pcdb.org.uk lists every registered boiler's efficiency figures. Searchable by brand and model.

Understanding the percentage

A 94% ErP boiler converts 94p of every £1 of gas into heat. The remaining 6p is lost through the flue. All modern condensing boilers score 90%+. Top performers reach 97–98%.

Net vs gross efficiency

Some older sources quote "net" efficiency; newer ones quote "gross." Net figures appear higher (e.g., "93% net" vs "82% gross" are the same boiler). The ErP label always uses gross calorific value. Compare like-for-like when researching.

What the difference means in practice

Going from 94% to 97% ErP efficiency saves approximately 3% on your gas bill. On a £1,200/year gas bill, that's £36/year. Over 12 years: £432 in savings — often less than the price premium between models. Focus more on reliability and warranty than the last 1–2 percentage points of efficiency.

A-rated minimum

Only ever consider A-rated boilers (90%+ ErP) for new installations. B-rated and below boilers are rarely sold for new installations — if you see one, ask why.