How much does it cost to install an air source heat pump in a flat?

That gap matters, because a flat is not simply a small house. The cost of the job is set by the heat loss of the property, the emitters that have to be changed, and the route the outdoor unit takes to the outside wall. In a block, two further costs sit outside the installer's control: the freeholder's consent and, where permitted development does not apply, a planning application.

What a heat pump costs in a flat: the figures that exist

The headline numbers are national averages across all property types, and they disagree with each other by a margin that reflects different samples and different dates. The average cost of installing an air source heat pump is around £13,000¹. The Energy Saving Trust puts the typical cost at around £12,000², and a separate Energy Saving Trust estimate cited by Which? puts it at around £14,000³. MCS data gives an average of around £13,300 in 2025⁷. Citizens Advice recorded an average of around £13,000 in 2024⁸.

None of these is a flat figure. The nearest thing to one is the Scottish Government's retrofit work on multiple-ownership and mixed-use buildings, which modelled a heat pump cost of £8,000 for flats in 2030, alongside £7,500 for a bio-hybrid alternative⁹. The same body's small home and apartment case estimated around £6,000 to £8,000 combined with installation, depending on whether any radiators need to be replaced⁴. That is a modelled figure for a small property, not a quoted market price, and it predates the current grant levels.

What drives the spread is what the installer has to do beyond hanging the box. Cost includes one-off installation costs and some home retrofit costs such as replacing radiators¹⁰. Access to the ground, trenches or boreholes, brand, model and size of heat pump, property size and heat need, new build or existing property, and radiator or underfloor heating upgrades all move the number¹¹. In a flat, the last of those is often the largest single line.

Why flats often cost less than houses

A flat has less external envelope per square metre of floor than a house, so the heat loss is usually lower and the heat pump smaller. A smaller unit costs less, needs less refrigerant, and takes less time to commission. Air-to-air systems, which are more often installed in smaller properties such as flats and park homes, have outdoor units typically smaller than air-to-water heat pumps¹².

The counterweight is that flats often have less room for the work. A wet system needs somewhere for a cylinder if hot water is to come from the heat pump, and internal space is the constraint that most often decides the system type. Air-to-air heat pumps are particularly well suited to smaller homes and flats and can take up less wall space than traditional radiators¹³, which removes the cylinder question entirely but also removes the hot water.

There is also a running-cost caveat that applies to any property, flat or house. If the home is not well insulated, installing a heat pump may increase energy bills instead of reducing them, because electricity is more expensive than gas¹⁴. Air source heat pump efficiencies are higher in warmer parts of the country, making it easier for them to be cheaper than gas there¹⁵. Where a suitable time-of-use tariff is available, air source heat pumps should cost no more to run than a gas boiler and, in the right home, can be considerably cheaper¹⁶. Tariffs of this kind offer a set, cheaper rate per kWh regardless of where you live, or a discount against the region's standard tariff¹⁷.

For a household, the independence question is straightforward: a heat pump moves space and water heating off gas and onto electricity, which can be generated at home or bought on a tariff of your choosing. It does not remove dependence on the grid, and in a flat it does not remove dependence on the freeholder.

Air-to-air or air-to-water: which system fits a flat

Air source heat pumps are classified as air-to-air or air-to-water depending on whether the heat distribution system in the building uses air or water¹⁸. Both absorb heat from the outside or surrounding air and transfer it into usable heat in the home for space or water heating, or both¹⁹. An air-to-water unit transfers heat drawn from surrounding air to water in a wet central heating system²⁰.

The choice usually turns on hot water. An air-to-water system can serve both heating and hot water, which is why it carries the larger grant. An air-to-air system heats air only, so a separate source of hot water is needed, and it attracts £2,500 rather than £7,500⁵. Air source heat pumps are easier and cheaper to install than ground source because they do not use buried pipes²¹, and in a flat with no garden that is not a choice at all.

Planning permission and freeholder consent: the flat-specific hurdles

Permitted development rights allow air source heat pumps to be installed on detached houses or blocks of flats without a planning application²². The rights apply to the installation, alteration or replacement of an air source heat pump on a house or block of flats, or within the curtilage of a house or block of flats, including on a building within that curtilage²³. But permitted development rules for air source heat pumps are more restricted for flats and shared buildings, and planning permission is more likely to be required²⁴.

Several conditions decide whether the rights apply. Planning permission is needed if the unit is on a pitched roof or less than 1m from the edge of a flat roof⁶. It is needed if the volume of the unit including housing exceeds 1.5 cubic metres within the curtilage of a dwelling house, or 0.6 cubic metres within the curtilage of a block of flats⁶. It is needed where there is an existing air source heat pump on a non-detached dwelling or block of flats, or two existing units on a detached dwelling house⁶. More than one air source heat pump on a non-detached property or a block of flats requires permission²⁵. The unit must be located within your property and meet the size and location limits²⁴.

For leasehold flats in England and Wales, the freeholder's approval is required for the installation of a heat pump on any part of the building or land for which they own or share the freehold²⁸. Leaseholders will usually require freeholder consent to install an air-to-air heat pump, because of either structural changes or external additions to the building²⁹. That consent is a private legal matter between leaseholder and freeholder, separate from the planning system, and it is the step most likely to delay a flat installation.

Grants: what the £7,500 BUS support means for flat owners

The Boiler Upgrade Scheme provides property owners with up to £7,500, or £9,000 for owners with properties heated by oil and liquid petroleum gas³⁰. The £7,500 applies to air-to-water heat pumps and ground source heat pumps⁵. From 21 July 2026 the grant value for an air-to-water heat pump in an off-gas-grid property replacing an oil or LPG heating system is £9,000⁵. Air-to-air heat pumps attract £2,500 in residential properties only⁵. In Wales, grants of £7,500 are available for air source and ground source heat pumps under the fossil fuel heating replacement scheme³¹.

The scheme has been at £7,500 for air source heat pumps since 23 October 2023³². The grant is not paid to the household: it is a voucher the installer redeems, and the amount is deducted from the quoted price. That means the figure a flat owner sees is the installer's price minus the grant, and the installer's price is the variable.

For a flat, the practical effect is that an air-to-water installation is supported at £7,500 while an air-to-air installation is supported at £2,500. Where a flat cannot take a wet system, the lower grant is the one that applies, and the difference of £5,000 is a real part of the cost comparison.

Retrofit challenges in blocks: shared decisions and technical complexity

The Heat Pump Ready Programme identified the barriers that hold back domestic heat pump uptake: the capital cost of heat pump system hardware and components, the in-property changes required, the internal and external space requirement, and the time taken for a heat pump install from accepted quote³³. Every one of those is sharper in a block of flats.

Space is the first constraint. A wet system needs a cylinder, and a flat may not have a cupboard to spare. The outdoor unit needs a wall, a balcony or a roof position that satisfies the 0.6 cubic metre curtilage limit for blocks and the 1m flat-roof edge rule⁶. Where the block is listed, consent adds a further stage²⁷.

Shared decisions are the second. The freeholder's approval is required for leasehold flats²⁸, and in a block the freeholder may be a residents' management company or a landlord with other priorities. Where more than one unit is proposed, planning permission is required²⁵, which turns an individual purchase into a collective process.

Cost is the third. The general retrofit figure for an air source heat pump in a semi-detached home is £12,000³⁴, and the modelled flat figure is £8,000 for 2030⁹. The difference between those two numbers is the reason a flat can be the cheaper job, but only where the flat can take the system at all. Suitability depends on space, budget and efficiency³⁵, and in a block the first of those is usually the binding one.