What size heat pump do I need?
Updated 25 September 2026. Every figure on this page comes from our published model; see how accurate it is.
A typical 3 bed semi is fitted with a heat pump of about 9 kW, and a 4 bed detached house about 12 kW. Insulation matters too: the same 3 bed semi needs about 7.5 kW once it is well insulated. Across every home that got the government grant between April and June 2026, the median heat pump was 8 kW. The table below gives the typical size for your home, and what that size costs.
Typical heat pump size for your home
These are the sizes typically installed in homes like yours. They come from how much heat a home of each type and size uses in a year, from government meter data for 39,502 homes, and sit in line with the sizes installers fit under the Boiler Upgrade Scheme, where the median heat pump in April to June 2026 was 8 kW and the middle half were between 6 kW and 10.8 kW.
| Home | Poorly insulated | Average | Well insulated | Recently retrofitted |
|---|---|---|---|---|
| 1 bed flat | 5 kW | 4.5 kW | 4 kW | 4 kW |
| 2 bed flat | 6.5 kW | 6 kW | 5 kW | 4 kW |
| 2 bed mid-terrace | 6.5 kW | 5.5 kW | 5 kW | 4 kW |
| 3 bed mid-terrace | 9 kW | 8 kW | 7 kW | 5 kW |
| 3 bed end-terrace | 9.5 kW | 8.5 kW | 7 kW | 5 kW |
| 3 bed semi | 10 kW | 9 kW | 7.5 kW | 5.5 kW |
| 2 bed bungalow | 8.5 kW | 7.5 kW | 6.5 kW | 4.5 kW |
| 3 bed bungalow | 10.5 kW | 9.5 kW | 8 kW | 6 kW |
| 3 bed detached | 10.5 kW | 9.5 kW | 8 kW | 6 kW |
| 4 bed semi | 14 kW | 12.5 kW | 10.5 kW | 8 kW |
| 4 bed detached | 13.5 kW | 12 kW | 10 kW | 7.5 kW |
| 5 bed detached | 17.5 kW | 16 kW | 13.5 kW | 10 kW |
Poorly insulated means little loft or wall insulation. Recently retrofitted means insulated walls, a full loft and good glazing. See our methodology for how size follows heat demand.
Your installer decides the exact size
A table can tell you what homes like yours usually have. It cannot tell you what yours needs. For the Boiler Upgrade Scheme, an MCS certified installer has to calculate the heat lost from every room on a cold day and size the heat pump to cover it, plus hot water. Ask to see that calculation before you accept a quote. Two quotes that differ by several kW for the same house are a sign that one of them has not done it properly.
Bigger is not safer. An oversized heat pump costs more, and it switches on and off more often in mild weather, which can lower how efficiently it runs. The right size is the smallest that keeps your home warm on a cold day.
What each size costs
Price rises with size, but not in step with it: much of an installation is fixed cost, so a small heat pump is not much cheaper than a mid-sized one. These figures are the median recorded by installers under the Boiler Upgrade Scheme in 2025/26 for a heat pump of each size.
| Home, average insulation | Typical size | Median installed | Middle half of installs | Median after £7,500 grant |
|---|---|---|---|---|
| 2 bed flat | 6 kW | £11,800 | £10,000 to £14,500 | £4,300 |
| 3 bed mid-terrace | 8 kW | £12,400 | £10,500 to £15,000 | £4,900 |
| 3 bed semi | 9 kW | £12,700 | £11,000 to £15,500 | £5,200 |
| 4 bed detached | 12 kW | £14,700 | £12,500 to £18,000 | £7,200 |
| 5 bed detached | 16 kW | £16,100 | £14,000 to £19,500 | £8,600 |
Homes replacing oil or LPG get a £9,000 grant instead of £7,500 until March 2027. For your own home, use the heat pump calculator, or build a full retrofit plan that sizes the heat pump for your home after insulation.
How to need a smaller heat pump
Everything that cuts the heat your home loses also cuts the size of heat pump it needs. For a 3 bed semi, going from average to good insulation takes it from about 9 kW to about 7.5 kW. The measures that do most, measured in real homes by the government, are solid wall insulation (a median 17.3 per cent less gas) and cavity wall insulation (12.0 per cent). See whether cavity wall insulation is worth it and radiator sizing for heat pumps.
Get heat pump quotes for your home
Tell us about your property and we will pass your request to up to three MCS-certified heat pump installers covering your postcode. It is free and there is no obligation to go ahead.
- MCS-certified installers only
- £7,500 grant, or £9,000 replacing oil or LPG
- Free, with no obligation
Frequently asked questions
What size heat pump do I need for a 3 bed semi?
Most 3 bed semis with average insulation are fitted with a heat pump of about 9 kW. A well insulated one is nearer 7.5 kW and a poorly insulated one nearer 10 kW. The exact size comes from the room by room heat loss calculation your installer must do.
What size heat pump do I need for a 4 bedroom house?
A 4 bed detached house with average insulation typically has a heat pump of about 12 kW, and a 4 bed semi about 12.5 kW. Insulating first can bring that down, and a smaller unit costs less to buy.
Is a bigger heat pump better?
No. An oversized heat pump costs more to buy and switches on and off more often, which can lower its efficiency. The right size is the smallest that meets your home's heat loss on a cold day, which is what the installer's heat loss calculation works out.
How is heat pump size worked out?
An MCS certified installer calculates the heat lost from each room on a cold design day, from its size, walls, windows, floor and roof, and sizes the heat pump to cover that plus hot water. That calculation is required for the Boiler Upgrade Scheme grant.
Data sources
- DESNZ, Boiler Upgrade Scheme statistics, August 2026, Tables A1.3A and Q1.1A.
- DESNZ, National Energy Efficiency Data-Framework 2026, consumption data and impact of measures tables.
- MCS, find a certified installer.