Reality · Aggregate · Published trial

What 742 UK homes told us about heat pumps.

Between 2020 and 2023, Nesta's Electrification of Heat demonstration installed heat pumps in a representative sample of British housing across three regions. It is the closest thing we have to an honest national field test; here is what the published findings show, and, just as importantly, what they don't.

The headline you can trust.

The trial recruited a mixed sample deliberately: pre-war terraces alongside 1970s semis and modern flats, across the North East, South East and Wales. Every home received either an air source, ground source or high-temperature heat pump, sized by the installer to the property as-found. There was no requirement to pre-insulate or to change radiators unless the design demanded it. The point was to see what a normal British home does when you fit a heat pump to it.

The published seasonal performance factor across the fleet came in at roughly 2.8 for air source systems and 3.4 for ground source, measured over a full heating season with metered inputs and outputs. That is below the marketing figures manufacturers quote against ideal conditions and well within the range that makes a heat pump cost-competitive with a gas boiler on current tariffs, provided the electricity price is on a heat-pump-friendly plan.

Every property archetype in the trial ended the winter warm. Not a single home was left uncomfortable by the technology itself.

Where the trial got interesting.

The distribution mattered more than the average. High-temperature heat pumps in unimproved Victorian and Edwardian properties delivered a seasonal performance factor around 2.4 to 2.6, comfortably above the break-even point but noticeably below the fleet mean. Standard air source units in well-insulated 1990s and later homes cleared 3.0 without difficulty. The pattern is the one the physics predicts: fabric quality is the biggest single variable, and it swings the running cost more than the choice of unit.

Installer variation was the other significant finding. Homes served by installers with prior heat pump experience saw markedly higher measured performance than those served by first-time installers, controlling for property type. The takeaway is not that heat pumps are hard; it is that commissioning, flow temperature setting and control setup are the parts that decide the final number, and they reward experience.

Comfort feedback was overwhelmingly positive across the sample, with a small minority of homes reporting the shift from short bursts of very hot radiator surfaces to steady lower-temperature output took a few weeks to get used to. Noise complaints were rare and, where they occurred, concentrated in installations where the outdoor unit sat close to a bedroom window; a siting decision, not a product one.

The trial did not price the installation itself; that is a separate policy question. It measured what the systems did once installed.

What the trial explicitly doesn't tell us.

The demonstration ran during a period of unusually volatile electricity pricing and did not attempt a controlled tariff comparison. Running-cost claims derived from it need to be read alongside a current tariff, not extrapolated as a fixed pence-per-kilowatt figure. The Cost Decision Engine on this site handles that separately.

It also sampled installer quality across only three regions, and cannot answer whether a good installer is available in every UK postcode. It is evidence that heat pumps work in British homes when installed well; it is not evidence that installation quality is uniform across the country.

Why we think thisOpen

Reasoning

Nesta led the Electrification of Heat project on behalf of the Department for Energy Security and Net Zero (formerly BEIS). The final report and supporting datasets were published in 2023 and are publicly available; the seasonal performance figures cited here are the fleet-level averages from that publication, not aggregated third-party interpretations.

Installer-variation findings are from the project's own analysis of measured versus modelled performance across the participating installers, published as a supplementary technical note.

Assumptions

742 UK homes across three regions (North East, South East, Wales), 2020 to 2023.
Seasonal performance factor measured with metered heat output and electrical input over full heating seasons.
Fleet-level averages; individual homes span a wider range and the distribution is the story more than the mean.

Sources

Electrification of Heat demonstration project: final report — Nesta / Department for Energy Security and Net Zero (2023)
Primary publication; the source for the 2.8 (ASHP) and 3.4 (GSHP) seasonal performance factors used above.
Electrification of Heat: interim findings on installer variation — Nesta / DESNZ technical note
The evidence base for the installer-quality observations; measured versus modelled performance across participating installers.
Heat Pump Association: heat pump installer statistics (annual) — Heat Pump Association
Independent trade body data used to sense-check the trial's installer capacity findings against the wider market.

If this were our house

If this were our house, we'd treat this trial as the floor of what is possible, not the ceiling.

1
Read the fabric first. A pre-heat-pump insulation and airtightness review moves the seasonal performance figure more than any product choice. The trial's own distribution is the argument for this.
2
Pick the installer before the unit. The trial's installer-variation finding is the single most actionable takeaway; a strong installer with a modest unit will outperform a weak installer with a premium one.
3
Model the tariff separately. Trial averages are performance evidence; running cost is a live tariff question that changes every few months. Don't let one substitute for the other.

This is aggregate evidence, not a case study of your house. Use it to set expectations, then run the Heating decision for the specific archetype you're in.

Questions this page hasn't answered.

Does the trial say heat pumps work in every UK home?

It says they worked in every archetype in the sample, warmly, over full winters. It does not say they are the cheapest choice in every home on every tariff; running cost is a separate calculation that depends on the current price of electricity and gas.

What about hybrid systems?

Hybrid gas-plus-heat-pump installations were a small part of the trial and are outside the fleet averages quoted here. They remain an option worth costing separately in homes where a full heat pump swap is disruptive.

When will there be a single-home entry in this layer?

When we have a home with measured before-and-after data, a named tariff, and the homeowner's consent to publish the raw numbers. Not before.

Evidence apparatus

Last reviewed: 4 July 2026
Evidence quality: High· Named primary source with a documented methodology and published dataset.

Primary sources

Electrification of Heat demonstration project: final report · Nesta / DESNZ (2023)Primary publication for the fleet-level seasonal performance figures used above.
Electrification of Heat: installer variation technical note · Nesta / DESNZMeasured versus modelled performance across participating installers.
Heat Pump Association annual installer statistics · Heat Pump AssociationIndependent trade-body data used to sense-check installer-capacity findings.

Assumptions

742 UK homes across three regions (North East, South East, Wales), 2020 to 2023.
Seasonal performance measured with metered heat output and electrical input over full heating seasons.
Fleet-level averages; individual homes span a wider range and the distribution is the story more than the mean.

Related evidence

Changelog

4 July 2026First publication of the Reality layer entry.