What the trial found
The best UK evidence is the Electrification of Heat Demonstration Project, run by Energy Systems Catapult for the government. It installed 742 heat pumps in a range of homes, monitored them, and reported in December 2024. 163 of the installations, 22% of the total, were in properties built before 1945. For the 428 air source heat pumps analysed, the report found no significant difference in seasonal performance by house type or age, concluding that where a trained installer recommends a heat pump for a property, house type or age should not affect performance.
Its 2021 findings said the same thing in broader terms: there is no property type or architectural era that is unsuitable for a heat pump (December 2021). The suggestion that some archetypes are unsuitable, in the project’s words, was not supported by its experience and data. That is a sound basis for dropping the blanket “heat pumps do not work in old houses” line.
It is not a case of no difficulty. The same trial said older homes presented a greater challenge in designing the system, and that is the part that matters if you own one.
The real hurdles
In the trial, pre-1919 properties, which the report notes are about 20.6% of UK homes, were more likely to have technical barriers than other property types. Mid-terraces more often hit practical barriers, mainly outdoor space and noise. For old houses, the usual difficulties are these:
- Higher heat loss, particularly with solid walls, single glazing or open chimneys, which means a larger unit and radiators or heat emitters than a newer house of the same size.
- Pipework and emitters. Old systems may have small-bore or awkward pipework, and rooms with limited wall space for larger radiators.
- Space for a hot water cylinder in a house that had a combi boiler and no airing cupboard. See the cylinder guide.
- Siting the outdoor unit in a terrace or on a street-facing wall. See planning permission.
- Variable results. The trial measured a median air source seasonal performance of 2.78 to 2.93, with a wide spread that the report links in part to design and installation quality. In an old house the design is where the work lies.
We have not found a robust, sourced figure separating the performance of solid-wall homes from the rest, so we do not quote one. The honest position is that the room-by-room heat-loss calculation is what handles this house by house.
Listed buildings and conservation areas change where an outdoor unit can go, so read heat pump planning permission before you agree a position with an installer.
Radiators and flow temperature
A heat pump is most efficient when the water it makes is not very hot. In the trial’s data, median COP was 3.5 when making 35°C flow, 2.38 at 55°C and 2.02 above 65°C. In a house with high heat loss, hitting a low flow temperature means larger radiators, some underfloor heating, or both, or improving the fabric so the radiators you have are enough. A good survey identifies room by room which radiators need to change and the quote itemises them. If the quote does not, ask. More detail is in the sizing and radiators guide.
Insulation and the grant
Insulation and draught-proofing help any heating system and shrink the heat pump you need to buy. But for the Boiler Upgrade Scheme in England and Wales they are not conditions: the insulation requirement was removed on 8 May 2024, and a valid EPC is no longer required (relaxed from 28 April 2026; the installer provides the EPC reference if one exists, otherwise other evidence). The grant is £7,500 for air-to-water and ground source, or £9,000 where the home has no mains gas and the heating being replaced is oil or LPG, for applications up to 31 March 2027. Some older rural homes are off the gas grid, and the £9,000 band also needs oil or LPG heating: see the £9,000 band. For all the tests, see eligibility.
The official median installed cost of an air source heat pump in 2026 Q3 was £12,826, which is about £5,326 after the £7,500 grant. An old house with a lot of emitter work may be above that median, so compare written quotes and see the cost page.
Listed and conservation properties
For air source heat pumps, England’s permitted development rights (Class G of the General Permitted Development Order) do not apply to listed buildings or their curtilage, so a unit there needs the local planning authority’s view on what consent is required. In a conservation area or World Heritage Site, the rules restrict a unit on a wall or roof fronting a highway. Other limits include a maximum of 2 units on a detached house and 1 otherwise, and a compressor unit volume of 1.5 cubic metres.
Ground source heat pumps have no outdoor unit and fall outside those air source limits, which makes them worth considering where there is garden or land and the budget: the median cost is higher, £34,630. Start any listed-building project with a conversation with the council’s conservation officer before spending on design. Scotland and Wales have their own planning rules and funding; see the country-by-country page.
What to do next
- Get a room-by-room heat-loss survey from an installer who is MCS certified. Ask for it in writing, with the design flow temperature.
- Ask which radiators change and what that adds to the price.
- Check planning status if the house is listed, in a conservation area or a terrace.
- Compare two or three quotes with the checklist.
- Decide fabric measures by cost and benefit, not because the grant demands them.
Doubts about heat pumps in older houses
“My house is Victorian and draughty. Surely it needs insulating first.”
Insulation and draught-proofing make any heating system cheaper to run and shrink the heat pump you need, so they are worth doing where they suit the building. But they are not a condition of the grant: the insulation requirement was removed on 8 May 2024, and a valid EPC is no longer required (relaxed from 28 April 2026; the installer provides the EPC reference if one exists, otherwise other evidence). The heat-loss calculation tells you how large the system must be as the house stands.
In a very leaky house, a sensible order may be fabric first, because the heat pump you would otherwise need is larger and costs more.
“A listed building will not be allowed one.”
Not necessarily, but the usual permitted development route for air source units does not apply to listed buildings or their curtilage, so you would need to check what permissions are required with the local planning authority. A ground source system is a different case and is described below.
Listed building consent can be slow and the answer varies by council and building. Ask the authority early, before you pay for a design.