Church of England orders parish to rip out brand new gas boilers

I’m no kind of expert, just assumed that what companies quote is the standard metric, which maybe it isn’t. Well, almost certainly isn’t, from your reply. So I asked Grok and got a great deal more confused! This is what Grok said:

**Typical efficiency of modern condensing boilers in the UK**

As of 2026, virtually all new gas boilers installed in the UK are condensing models, and they typically achieve efficiencies of **90-94%**, with top models reaching up to **98%**. Manufacturers commonly advertise figures around 92-94% for most standard models, while premium ones (e.g., from Viessmann or Worcester Bosch) often hit 94-98%. In real-world conditions, efficiencies can be lower if the system isn’t optimised (e.g., due to high flow temperatures preventing full condensation).

**Legal standards for new boilers**

Yes, there are strict legal requirements:

– Since 2005, nearly all new or replacement domestic gas boilers must be condensing types (with rare exemptions for impractical installations).
– Under the Boiler Plus legislation (introduced in 2018 and still in force), all new gas combi boilers in England must achieve a minimum ErP (Energy-related Products) efficiency rating of **92%** (equivalent to an A-rated label). This applies UK-wide through ecodesign regulations.
– Additional measures like time/temperature controls are mandatory, and for combi boilers, features such as weather/load compensation or smart controls are often required to maximise efficiency.

No major changes to the 92% minimum have been implemented by 2026, though consultations have explored higher standards or hydrogen-ready requirements.

**How efficiency is calculated**

Boiler efficiency in the UK is primarily measured using the **ErP rating** (since 2015), which replaced the older SEDBUK system for most purposes:

– **ErP (Energy-related Products)**: This EU-derived directive rates boilers from A+++ to G based on seasonal space heating efficiency. It’s calculated using standardised laboratory tests that simulate typical annual usage, including full-load, part-load, standby losses, and auxiliary energy use. The test accounts for the boiler’s ability to condense (recover latent heat from flue gases). A minimum of 92% is required for new gas boilers, meaning at least 92% of the fuel’s energy is converted to useful heat under test conditions.
– **SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK)**: The older UK-specific system (still referenced for some calculations like EPCs) uses similar lab tests but adjusts for typical UK weather, usage patterns, and factors like boiler type or ignition. Modern boilers typically score 89-90% under SEDBUK, even if ErP is 92-94% (due to slight methodological differences).

In practice, condensing efficiency improves when return water temperatures are low (below ~55°C), allowing more heat recovery from vapour condensation—adding up to 10-11% extra over non-condensing designs.

I have been quoted a new boiler, rather expensive, with a 30 year guarantee on the stainless heat exchanger, which promises in the high nineties efficiency. Though I don’t know how that is measured.

A friend has his efficiency tested by the local engineer every annual maintenance. Again, not sure how he does it, but this is a non-condensing boiler about 20 years old, and he gets quoted readings of 85%.

But maybe they are not measuring the same thing as what you quote?

Either way of course your main point, the idiocy of converting gas to electricity and running a heat pump, still applies.