Heat pump for a 1930s semi: cost and running costs
The short answer
- £11,000 to £15,500 installed, with a median of £12,700, or £3,500 to £8,000 after the £7,500 grant
- About 9 kW for a 1930s semi with average insulation, falling to about 7.5 kW once well insulated
- £666 a year to run on an 18.7p heat pump tariff, against £877 for gas and £937 on a standard tariff
Updated 25 September 2026. Every figure on this page comes from our published model; see where our data comes from.
A typical 1930s semi is a 3 bed house, and many were built with cavity walls that have since been filled. With average insulation, a 1930s semi typically needs a heat pump of about 9 kW, falling to about 7.5 kW once it is well insulated. Installers recorded a typical cost of £11,000 to £15,500 for a heat pump of that size under the Boiler Upgrade Scheme, with a median of £12,700. After the £7,500 grant, most pay £3,500 to £8,000.
What it costs
Size, and so price, follows how much heat the home loses. These are the typical size and the recorded installed cost for a 1930s semi at each level of insulation. The installed cost is the whole job as installers reported it to the scheme: the heat pump, hot water cylinder, labour and VAT, before the grant. Some homes also need larger radiators, which can add to it; see radiator sizing.
| Insulation | Typical size | Median installed | Middle half of installs | Median after £7,500 grant |
|---|---|---|---|---|
| Poorly insulated | 10 kW | £13,300 | £11,500 to £16,000 | £5,800 |
| Average | 9 kW | £12,700 | £11,000 to £15,500 | £5,200 |
| Well insulated | 7.5 kW | £12,300 | £10,500 to £15,000 | £4,800 |
| Recently retrofitted | 5.5 kW | £11,700 | £10,000 to £14,000 | £4,200 |
Middle half of installs: the scheme's lower and upper quartile, scaled to each median. Homes replacing oil or LPG get £9,000 instead of £7,500 until March 2027.
What it costs to run
Running costs use the median efficiency measured across 428 heat pumps in the government's Electrification of Heat trial, at the Ofgem price cap for October to December 2026. The tariff matters more than almost anything else: see heat pump tariffs.
| Insulation | Gas boiler | Heat pump, standard rate | Heat pump tariff, 18.7p |
|---|---|---|---|
| Poorly insulated | £973 | £1,134 | £806 |
| Average | £877 | £937 | £666 |
| Well insulated | £745 | £726 | £516 |
| Recently retrofitted | £544 | £497 | £353 |
What to check in a 1930s semi first
Three things decide how well a heat pump works in a house of this age. First, the walls: if the cavity has never been filled, filling it is one of the biggest cuts in heat loss you can make, a median 12.0 per cent less gas in homes the government measured. Second, the floor: many 1930s houses have suspended timber floors that are draughty, which underfloor insulation and draught-proofing address. Third, the radiators: rooms such as a bay-fronted lounge may need a larger radiator to stay warm at the lower flow temperatures heat pumps run at. An MCS installer's room by room heat loss survey shows which rooms need what.
See also the EPC rating of a 1930s house.
Compared with similar homes
| Home, average insulation | Typical size | Installed, middle half | Heat pump tariff running cost |
|---|---|---|---|
| 3 bed semi | 9 kW | £11,000 to £15,500 | £666 |
| 3 bed end-terrace | 8.5 kW | £11,000 to £15,500 | £624 |
| 3 bed mid-terrace | 8 kW | £10,500 to £15,000 | £593 |
| 3 bed detached | 9.5 kW | £11,000 to £15,500 | £708 |
For your own figures, use the heat pump calculator, or build a retrofit plan that puts insulation first and sizes the heat pump for the home after it.
Frequently asked questions
How much does a heat pump cost for a 1930s semi?
Typically £11,000 to £15,500 installed for a 9 kW heat pump, with a median of £12,700, from what installers recorded under the Boiler Upgrade Scheme in 2025/26. After the £7,500 grant that is £3,500 to £8,000, or £2,000 to £6,500 if you are replacing oil or LPG.
Is a heat pump cheaper to run than gas in a 1930s semi?
On a 18.7p heat pump tariff, yes: about £666 a year against £877 for gas with average insulation. On a standard electricity tariff it costs about £937, a little more than gas. Both figures are energy only; gas also carries a £108 a year standing charge you save if you cap the supply.
What size heat pump does a 1930s semi need?
About 9 kW with average insulation, and less once it is well insulated. The exact size comes from the room by room heat loss calculation an MCS installer must do. See our guide to heat pump sizes.
Data sources
- DESNZ, Boiler Upgrade Scheme statistics, August 2026, Tables A1.3A and Q1.1A.
- Energy Systems Catapult for DESNZ, Electrification of Heat trial, heat pump performance report, December 2024.
- DESNZ, National Energy Efficiency Data-Framework 2026.
- Ofgem, energy price cap, October to December 2026.