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Heat pumpsWhich homes suit a heat pump, and which need work first
The usual advice is that heat pumps suit new, well insulated homes and nothing else. The largest British field trial to date says otherwise. What separates a good outcome from a bad one is not the house, it is what the designer does with it.
Updated 4 August 2026 · written by the Clearline guidance team
What the trial actually found
The government funded Electrification of Heat demonstration project installed 742 heat pumps across a deliberately broad spread of British housing: Victorian terraces, 1960s flats, pre-war semis and everything in between. Its published conclusion was that there is no property type or architectural era unsuitable for a heat pump.
That is a stronger statement than most sales literature makes, and it is worth reading precisely. It does not say every house performs identically. It says no house is off the table. The median in situ seasonal performance factor across the air source systems monitored was 2.80, and performance varied widely between installations.
The variation is the finding
The gap between the best and worst performing installations in that trial was larger than the gap between property types. A well designed system in a Victorian terrace beats a badly designed one in a modern semi. Which means the survey and the designer matter more than the year your house was built.
What genuinely makes a house easier or harder
Age is a poor predictor. These five things are much better ones, and every one of them is measurable rather than a matter of opinion.
| Factor | Easier | Harder | Why it matters |
|---|---|---|---|
| Heat loss | Lower calculated heat loss per room | High heat loss from solid walls or large single glazed areas | Sets the kW size of the unit and the size of every radiator |
| Existing emitters | Oversized radiators or underfloor heating | Small single panel radiators sized tight to a boiler | Decides how low the flow temperature can go, which drives running cost |
| Outdoor space | Rear or side wall with airflow and a route for pipework | No rear elevation, shared access, tight terraced yard | The unit needs a compliant location under permitted development |
| Cylinder space | Existing airing cupboard or old cylinder position | Combi boiler with the cupboard converted years ago | A heat pump stores hot water rather than heating on demand |
| Neighbour proximity | Detached or generous side return | Terraced with habitable room windows close by | The MCS 020 (a) sound calculation must pass at 37 dB(A) or lower |
None of these five rules a property out on its own. They change the specification and the cost, which is exactly what a survey exists to establish.
Older and solid walled homes
Solid walled Victorian and Edwardian housing is the case people worry about most, and it was explicitly in the trial. The honest position is that a solid walled house has a higher calculated heat loss, so it needs a bigger unit and larger emitters to hold the same room temperature at heat pump flow temperatures. That is a cost question, not a feasibility question.
There is also a genuine lever available in older homes that is often missed. Current R290 flagship units reach 70 to 75C flow, so a house that cannot economically get to 45C flow across every room is not stranded. It runs warmer and less efficiently, which is a worse outcome than a low temperature design but still a working system. Daikin's Altherma 3 H HT high temperature range is built specifically for that case, quoting flow up to 70C and outputs of roughly 11 to 13 kW across three classes.
Not sure which category your house falls into? The free remote design call works it out from your actual property, on video, with nothing to sign.
Get your free quote →Flats and terraces
Permitted development in England allows up to two air source units on a detached house or bungalow and one on anything else, including flats and terraced houses. The volume limit is 1.5 cubic metres per unit on houses and 0.6 cubic metres on blocks of flats. For a flat or a mid terrace the constraint is usually location and the sound calculation rather than the kit itself.
In a conservation area the unit has to sit on the rear elevation and must not face a highway. Listed buildings need both planning permission and listed building consent. Those rules are set out in full in heat pump noise and planning rules.
The case that performs worst
The trial gives one clear warning, and it is not about a property type. Hybrid systems, a heat pump paired with a retained gas boiler, performed worse than heat pump only systems, with a median heat pump efficiency of 2.37 against 2.80 for full heat pump installations. Hybrids are also excluded from the Boiler Upgrade Scheme, so the grant and the performance data point the same way.
Insulation first, but not insulation only
Reducing heat loss lowers the size of the unit and the size of the radiators, so it reduces both the install cost and the running cost. It is a good idea. What it is not is a legal or scheme requirement: the GOV.UK Boiler Upgrade Scheme eligibility page carries no EPC condition and no insulation condition.
What to do before you commit
- Get a room by room heat loss calculation, which the MCS design standard requires before any certified installation anyway.
- Ask for the design flow temperature in writing, because that number drives your bills for the next twenty years.
- Ask which specific radiators are being changed and why, room by room, not as a package price.
- Confirm where the outdoor unit will sit and that the MCS 020 (a) sound calculation passes at that position.
- Check the hot water plan, including where the cylinder goes and whether the immersion is needed for legionella cycles.
Local factors change the picture too, from typical property stock to installation team availability. Every county page on this site carries a local calculator, so start with our coverage map. The full heat pumps guide sits alongside it, and if you are considering solar panels at the same time, the electrical load a heat pump adds is worth planning into that decision rather than bolting on later.
Clearline gives independent guidance and does not install. Installations are carried out by an MCS-certified installation team for your area.
Property questions, answered
Is my house too old for a heat pump?
The Electrification of Heat demonstration project installed 742 heat pumps across all housing types and eras and concluded no property type is unsuitable. Older solid walled homes have higher heat loss, so they need larger units and larger emitters, which raises the install cost. It changes the specification rather than the answer.
Do I have to insulate before I can get a heat pump?
Not as a condition. The GOV.UK Boiler Upgrade Scheme eligibility page contains no EPC or insulation requirement. Insulation still lowers your heat loss, which lets you fit a smaller unit at a lower flow temperature, so it usually pays for itself twice over in a heat pump project.
Can I have a heat pump in a flat?
Permitted development in England allows one air source unit on a block of flats, with a volume limit of 0.6 cubic metres, against 1.5 cubic metres on a house. The practical barriers are usually finding a compliant location, passing the MCS 020 (a) sound calculation, and getting freeholder consent, which is a separate matter from planning.
Is a hybrid heat pump plus gas boiler a safer bet?
The trial data does not support it. Hybrid systems recorded a median heat pump efficiency of 2.37 against 2.80 for full heat pump systems. Hybrids are also excluded from the Boiler Upgrade Scheme, so you would be paying more for a system that performed worse in monitoring.
What if I only have a combi boiler and no cylinder?
You will need to find space for a hot water cylinder, because a heat pump heats water to a store rather than instantly at the tap. Old airing cupboards, loft space and utility rooms are the usual answers. It is one of the first things a survey looks at.
Does a listed building rule out a heat pump?
No, but it changes the process. A listed building needs planning permission and listed building consent rather than relying on permitted development. In a conservation area the unit must be on the rear elevation and must not face a highway.
See the numbers next: Tesla Powerwall 3, installed, or what a battery costs.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- Energy Systems Catapult, Electrification of Heat demonstration project: 742 installations, all housing types finding, median air source SPF 2.80, hybrid median 2.37, performance variation between installations es.catapult.org.uk
- The Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2025, SI 2025/560, in force 29 May 2025: Class G unit counts and volume limits legislation.gov.uk
- MCS 020 (a), Air Source Heat Pump Sound Calculation for Permitted Development Installations, Issue 1.0, July 2025 mcscertified.com
- GOV.UK, Boiler Upgrade Scheme: check if you are eligible, and what you can get gov.uk
- Daikin, Altherma 3 H HT product page and installer brochure: 70C flow, output classes, SCOP 4.71 at 35C daikin.co.uk
- MCS, MIS 3005-D Heat Pump Design Standard 2025 V1.0: room by room heat loss calculation requirement mcscertified.com
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