The Performance Gap
Britain is buying Heat Pumps, Solar and Batteries on the strength of a promise. The Government's own data shows the promise and the delivered performance are rarely the same thing.
Sources checked 10 October 2026. Listed at the bottom of the page.
The Government's own field data
91.9% of the monitored Heat Pumps performed below their design rating.
The Electrification of Heat trial installed 742 Heat Pumps. 483 homes had enough data to compare in-use performance with the design figure, and 91.9% of them fell short.
Source: Energy Systems Catapult for DESNZ, Electrification of Heat report, December 2024. Dec 2024 report
Key facts, sourced
- 91.9% of the Heat Pumps compared ran below their design rating. On average they ran 0.66 below it, about 18% short (in-use SPF against the design SCOP).Energy Systems Catapult for DESNZ, Electrification of Heat: 483 of the trial's 742 homes. Dec 2024 report
- For air source Heat Pumps, the gap between design and in-use performance is widening in the most recent installations. The design figures have gone up; the measured performance has stayed about the same.rb&m, independent report funded by DESNZ, RECC and GSHPA: Ofgem RHI data 2017–2022, 1,717 systems. Sept 2024 report
- Estimate-based EPCs are being reformed. The Home Energy Model will replace SAP, and new certificates with four headline ratings, one of them for the heating system, are planned for the second half of 2027. The exact date isn't fixed yet.MHCLG, Reforms to the Energy Performance of Buildings regime. GOV.UK, updated 9 Mar 2026
The number the brochure leaves out
In the DESNZ / Energy Systems Catapult Electrification of Heat demonstration (742 Heat Pumps installed, 483 homes with enough data to compare, report published December 2024), 91.9% of properties recorded in-use performance (SPF) below the design figure (SCOP) — a mean shortfall of −0.66, about 18% below design on average. Independent analysis of more than 1,700 Heat Pumps under Ofgem's Renewable Heat Incentive found the gap between designed and actual performance widening for air source Heat Pumps in the most recent installations. This is not a survey of opinion. It is the Government measuring its own programme.
Why the gap persists
Every commercial party in the chain is paid on the sale, not on the outcome. Comparison sites and lead-generators are paid per introduction. Manufacturers see only their own hardware. Suppliers sell the kilowatt-hours that inefficiency wastes. There is a structural disincentive to publish a system under-delivering — so, largely, nobody does.
The direction of travel
The way home-Energy performance is certified is changing. The Standard Assessment Procedure behind today's estimate-based EPCs is being replaced by the Home Energy Model, and reformed, multi-metric certificates — including a heating-system rating — are planned for the second half of 2027, with the exact date still to be agreed. The new heating-system rating will still be a modelled figure, not a reading from your meter. The conversation is moving from what a system was promised to do, to what it actually does.
Forty years in high-hazard process Engineering teaches one habit above all: you do not assume performance, you measure it. A designed figure is a hypothesis. The meter is the truth. SavingEnergy.com exists to hold that line for the British homeowner — plainly, independently, and with no product to sell you.
Direct answers about the performance gap.
What is the performance gap?
The difference between how efficiently a Heat Pump was designed to run and how efficiently it actually runs in the home. In the Government's Electrification of Heat trial, 91.9% of the Heat Pumps that could be compared ran below their design figure, on average about 18% below.
Does that mean Heat Pumps don't work?
No. It's not because Heat Pumps don't work. It's because design, installation and settings get missed. That's exactly what an Engineer looks for.
How do I avoid it?
Ask for the design figures in writing, compare more than one quote, and put your questions to the installer before you commit.
More plain-English guides
Written by an Engineer with 40+ years on safety-critical systems. Free to read, sources checked and dated.
Sources
All checked 10 October 2026.
Energy Systems Catapult for DESNZ, Electrification of Heat Demonstration Project – Heat Pump Performance Data Analysis Report, December 2024 (section 1.4.5; tables 11.1 and 11.2) — es.catapult.org.uk
rb&m (Colin Meek and Jamie Newman), In-Situ Heat Pump Performance: Analysis of Ofgem Data 2017–2022, September 2024, an independent report funded by DESNZ, RECC and GSHPA — recc.org.uk
MHCLG, Reforms to the Energy Performance of Buildings regime, consultation page updated 9 March 2026 — gov.uk
GOV.UK guidance, Standard Assessment Procedure, updated 8 June 2026 — gov.uk
General information only. It isn't a Survey and doesn't replace your installer's design or MCS checks.