Air source heat pumps: how they work, what they cost and whether one suits your home

How an air source heat pump heats your home, how the types compare, what one costs and which grants apply in England and Wales, Scotland and Northern Ireland, and the pros and cons worked through on one example home.

By the Heat Pump Report editorial team · Last updated: 30 October 2026 · Sources checked: 29 October 2026 · Reading time: 14 min

An air source heat pump takes warmth from the outside air and uses electricity to raise it to the temperature your radiators and hot water need, replacing a gas, oil or LPG boiler. In the government-funded Electrification of Heat trial, air source heat pumps delivered a median 2.78 units of heat for every unit of electricity over a year. Installed, one costs a median £12,826 in England and Wales (July to September 2026, before any grant); if your home qualifies, the £7,500 Boiler Upgrade Scheme grant there brings that to £5,326. In our example 1970s semi, a heat pump with a SCOP of 2.8 costs about the same to run as the existing gas boiler at the October to December 2026 price cap.

At a glance

Price. £12,826 median installed price in England and Wales before the grant (grants paid July to September 2026), or £5,326 after the £7,500 Boiler Upgrade Scheme grant if your home qualifies.
Grants by nation. England and Wales: £7,500, or £9,000 for off-gas-grid homes replacing oil or LPG (applications properly made 21 July 2026 to 31 March 2027). Scotland: a Home Energy Scotland grant and optional interest-free loan. Northern Ireland: no grant open to all homeowners.
Running costs. In our example home, about the same as the existing gas boiler at SCOP 2.8 on October to December 2026 prices; more below a SCOP of 2.81, less above it.
First step. A room-by-room heat-loss survey by an MCS-certified installer; then, in England and Wales, the installer applies for the grant before work starts, while in Scotland you apply to Home Energy Scotland and wait for its written offer.

What is an air source (air-to-water) heat pump?

An air source heat pump system is an outdoor unit with a fan, an indoor (hydraulic) unit and usually a hot-water cylinder. In the UK the term means an air-to-water heat pump: it heats water for your radiators or underfloor heating and your taps, as a boiler does. Air-to-water units account for 94,545 of the 96,611 Boiler Upgrade Scheme grants paid in England and Wales to the end of September 2026.

It works like a fridge, except that it uses the warm side. A refrigerant circulates in a sealed loop through four stages:

Evaporator. The fan draws outside air across a coil; the colder refrigerant inside absorbs its heat and turns into vapour.
Compressor. An electric compressor squeezes the vapour, raising its pressure and temperature.
Condenser. The hot vapour passes its heat to the water in your heating system and turns back into liquid.
Expansion valve. The pressure drops, the refrigerant cools, and the loop starts again.

Cutaway of an outdoor heat pump unit with its fan, coil and compressor, connected through the house wall to an indoor unit that feeds a radiator and underfloor heating pipes — The outdoor unit collects heat from the air, the refrigerant loop raises its temperature, and the heating water carries it to your radiators or underfloor heating.

The lower the flow temperature (the temperature of the water sent to the radiators), the less electricity each unit of heat takes, so the design of the whole system matters as much as the box outside. The cycle, defrosting and cold-weather running are explained in how does a heat pump work. The diagram shows where the heat in our example home comes from.

Where 8,075 kWh of heat a year comes from

Example home

The heat pump takes electricity from the grid and heat from the outside air and gives both to the home as heat.

Per 10 kWh of heat: 4 kWh electricity + 6 kWh from the air

our central case

Heat and electricity, month by month

kWh of heat a month; the line is the electricity at SCOP 2.8

1,101 kWh265 kWh

Heat
Electricity
Highest
Lowest

What the year takes

Space heating: 6,460 kWh
Hot water: 1,615 kWhabout 20%, our assumption
Share from the air: 64%5,191 kWh of 8,075 kWh

Example semi-detached house from the 1970s (our assumption), 97 m²: 8,075 kWh of useful heat a year, 1,615 kWh of it for hot water (about 20%, our assumption). Electricity = heat ÷ seasonal performance factor; the rest comes from the air, and the factor includes the whole system’s electricity. Months: room heat by the degree hours for Birmingham (PVGIS), hot water evenly, electricity by the COP at the month’s temperature, adding up to the year. No solar panels or battery.

How much electricity the heat pump in the example house uses, how much heat it takes from the outside air and how much heat comes out for heating and hot water.

A year: 2,884 kWh of electricity and 5,191 kWh of heat from the air give 8,075 kWh of heat, 6,460 kWh for heating and 1,615 kWh for hot water; 2.8 kWh of heat per kWh of electricity.

Which type of heat pump suits your home?

Air source is the usual choice for a whole house. The alternatives differ in what they heat, what they need and what support they get:

Type	Heats	Hot water	Grant	Median price	Needs
Air source (air-to-water)	radiators, underfloor	yes	£7,500	£12,826	space outside for the unit
Ground source	radiators, underfloor	yes	£7,500	£34,630	trenches or a borehole
Air-to-air	room air	no	£2,500	no official median	a separate way to heat water
Hybrid (with a boiler)	radiators, underfloor	yes	none	no official median	a boiler kept alongside

With only 1,603 ground-source grants paid in total, its median moves a lot between quarters; the median ground-source system behind it was 15 kW, against 8 kW for air source. A hybrid keeps a boiler for the coldest days and gets no Boiler Upgrade Scheme grant; in Scotland, Home Energy Scotland funds neither hybrids nor air-to-air.

Monobloc or split, and the refrigerant

The two designs differ in what passes through your wall:

What differs	Monobloc	Split
Through the wall	heating water	refrigerant pipes
Refrigerant loop	sealed in the outdoor unit	connected on site
Refrigerant work	none on site	F-gas qualification for F-gas refrigerants

Two house walls side by side: on the left an outdoor unit joined to an indoor unit by red and blue water pipes, on the right an outdoor unit joined to a wall-hung indoor unit by grey refrigerant pipes — Monobloc (left): only heating water crosses the wall. Split (right): refrigerant pipes link the outdoor and indoor units.

The UK is largely a monobloc market: 98,946 of the 102,258 air-to-water heat pumps sold in 2025 were monoblocs, according to the Heat Pump Association. How the main models compare is in best air source heat pumps.

Many monoblocs use R290 (propane), a natural refrigerant; Mitsubishi Electric's 8 kW Ecodan R290 contains 1.0 kg of it, with a global warming potential of 0.02. Propane is highly flammable, so the maker sets a protective zone for an outdoor installation: for this model, 1 m around the unit and 0.3 m high. No window, door, vent, light well, drain or socket may sit inside it, and it must not extend onto a neighbour's property, a footpath or a driveway. In a small garden or a narrow side return, that can decide where the unit goes.

Outdoor heat pump unit in front of a house wall with a blue-shaded zone marked on the ground around it; inside the zone on the left is a light well with a basement window — The shaded protective zone around an R290 unit must stay clear. Here a basement window sits inside the zone, so the unit could not stand in this spot.

A few models are made to stand indoors, drawing outside air in and out through ducts in the wall, so there is no outdoor unit.

Drawing of an indoor heat pump unit in a room, with two air ducts running to openings in the outside wall and arrows showing air drawn in and blown out — An indoor air source unit: outside air reaches it through ducts in the wall and leaves the same way.

Price and support by UK nation

For grants paid from July to September 2026, the median air source job in England and Wales cost £12,826, as reported by MCS installers under the Boiler Upgrade Scheme, VAT included and before the grant; the median system was 8 kW. If your home qualifies, the installer takes the £7,500 grant off, which leaves £5,326. Prices by size and the extras older homes need are in heat pump cost.

What is left after the grant depends on where you live:

Nation	Support	Before any work
England and Wales	Boiler Upgrade Scheme: £7,500; £9,000 for off-gas-grid homes replacing oil or LPG (applications properly made 21 July 2026 to 31 March 2027)	the installer applies; get the voucher before work starts
Scotland	Home Energy Scotland: grant up to £7,500, plus £1,500 for eligible rural and island homes, and an optional interest-free loan up to £7,500	you apply and wait for the written offer
Northern Ireland	no grant open to all homeowners; NISEP schemes fully fund a heat pump for some lower-income owner-occupiers	depends on the scheme

In England and Wales you never receive the grant as money: Ofgem pays the installer, who takes it off your invoice. For the Boiler Upgrade Scheme your old gas, oil or LPG heating has to be fully replaced, not kept as a backup; the rule is written about heating, so ask your installer before you plan to keep gas for cooking. Who may qualify is in heat pump grants, Scotland in Home Energy Scotland grants and loans, and the off-gas route in replacing an oil boiler with a heat pump. A heat pump supplied and installed in your home carries 0% VAT until 31 March 2027, then 5%.

What it costs to run

Our example home is a 1970s semi-detached house in England with 97 m² of floor space, radiators and a gas combi boiler. It uses 9,500 kWh of gas a year, Ofgem's typical medium use, and we assume the existing boiler turns 85% of that into heat. On unit rates alone:

Heat needed: 9,500 kWh × 85% = 8,075 kWh a year.
Heat pump: 8,075 kWh ÷ SCOP 2.5 / 2.8 / 3.1 = 3,230 / 2,884 / 2,605 kWh of electricity × 26.32p = £850 / £759 / £686 a year.
Existing gas boiler: 9,500 kWh × 7.97p = £757 a year, so the break-even SCOP is 0.85 × 26.32 ÷ 7.97 = 2.81.

SCOP is the heat delivered for each unit of electricity over a year; we use 2.8, close to the trial median (see heat pump efficiency). Rates are the Ofgem price cap, GB average, direct debit, 1 October to 31 December 2026, standing charges left out. In Great Britain electricity carries no VAT until 31 March 2027 while gas carries 5%; with 5% VAT on electricity the break-even would be about 2.95 instead of 2.81. Your own result depends on the house, the installation and your tariff.

Energy cost a year, our example home

Heating	Gas boiler	Heat pump
Existing gas boiler	£757
Heat pump, SCOP 2.5		£850
Heat pump, SCOP 2.8		£759
Heat pump, SCOP 3.1		£686

Our example home: 8,075 kWh of heat a year, existing boiler at 85% (our assumption), unit rates from the Ofgem price cap for 1 October to 31 December 2026 (GB average, direct debit), standing charges and servicing left out.

The full calculation is in heat pump running costs, whether the switch pays for itself, including against a new boiler, in heat pump vs gas boiler, off-peak rates in heat pump tariffs, and pairing one with solar panels in heat pumps and solar panels.

What your home needs: heat loss, radiators and a cylinder

An older house doesn't rule one out: the Electrification of Heat trial found no statistically significant difference in performance by house type or age, although every home in it had first been judged suitable by trained designers. Three things decide it:

Heat loss, room by room. Under the MCS design standard MIS 3005-D, the installer calculates each room's heat loss, picks a heat pump that covers all of it without the backup electric heater, and gives you the room heat losses, design flow temperature and expected SCOP in writing before installation.
Radiators. A radiator sold as 1,500 W gives roughly 578 W when its water averages 45 °C in a 21 °C room (worked out with the manufacturer's correction factor), so some rooms may need a larger one. In England, a fully replaced wet heating system should be designed for a flow temperature of 55 °C or lower under Building Regulations guidance.
Space for hot water. A combi home needs room for a hot-water cylinder. In England an unvented cylinder is notifiable building work unless the installer self-certifies through a competent person scheme.

How to check your own home is in is my home suitable for a heat pump.

Where it goes: noise and planning

The outdoor unit needs a firm, level base, free airflow and a drain for the water that drips from it. In England and Wales it is usually permitted development if it passes the MCS 020(a) noise test (37 dB(A) at a neighbour's window) and the size and siting conditions, but not on a listed building, and conservation areas restrict where the unit can go. Scotland and Northern Ireland have their own rules: see heat pump planning permission and check with your local planning authority.

Air source heat pump pros and cons: are they any good?

Designed and installed well, yes: it heats your home and hot water on electricity alone, and in our example home it costs less to run than the existing gas boiler above a SCOP of 2.81 (October to December 2026 cap rates). In its favour:

One system for heating and hot water. It replaces the boiler for both, and some models can also cool (see the FAQ).
No fuel burned at home. No flue, no gas needed for heating and no oil deliveries.

The drawbacks, and what helps:

Drawback	In our example home	What helps
Upfront price	£5,326 after the grant at the median (England and Wales), against about £3,500 for a new gas boiler (government estimate)	the grant before work starts; like-for-like quotes
Efficiency depends on design	below SCOP 2.81 it costs more to run than the existing gas boiler	a room-by-room survey and the lowest workable flow temperature
Electricity prices	your bill follows the unit rate; no VAT on electricity in Great Britain only until 31 March 2027	a heat-pump or time-of-use tariff
Space	an outdoor unit, and a cylinder in a combi home	settle both positions at the survey
Noise and siting	37 dB(A) test at a neighbour's window (England and Wales)	distance, a solid barrier

"They don't work when it's freezing"

They do, though they use more electricity as the air gets colder. An MCS design has to keep every room at its target temperature on the coldest day the standard sets for your area (−3.0 °C in London and −5.9 °C in Glasgow on its colder values) and through repeated defrosts. The 8 kW R290 model above is rated to run down to −25 °C.

Outdoor heat pump unit standing in snow with frost on its fins and vapour rising from it, while meltwater drips into a gravel bed below — In frosty weather the unit melts ice off its coil automatically; the vapour and dripping water are part of normal running.

"You need underfloor heating"

It helps, because it runs cool, but radiators work if each is large enough for its room at the design flow temperature; the survey shows which need replacing.

"Gas boilers are being banned"

There is no ban on keeping or repairing a gas boiler in an existing home. The Future Homes Standard applies to new homes in England from 24 March 2027.

Checklist: your route to an air source heat pump

From first look to switch-on

Find your yearly gas or oil use on your bills.
Note where an outdoor unit and, in a combi home, a cylinder could go.
Book a room-by-room heat-loss survey with an MCS-certified installer.
Get more than one quote for the same scope.
In England and Wales, start work only once the grant voucher is issued; in Scotland, wait for Home Energy Scotland's written offer.
Ask the installer to confirm the unit meets permitted development, or whether you need planning permission.
After switch-on, compare tariffs that suit how your heat pump runs.

How to compare installers and their quotes is in choosing an MCS installer, and each stage from survey to switch-on in heat pump installation.

Figures that change

What	Value	Applies
Air source heat pump, installed	median £12,826	grants paid July–September 2026, England and Wales, before the grant
Ground source heat pump, installed	median £34,630	grants paid July–September 2026, England and Wales, before the grant
Boiler Upgrade Scheme grant	£7,500 air source or ground source; £2,500 air-to-air	England and Wales; air-to-air from 28 April 2026
Off-gas grant	£9,000	England and Wales; oil or LPG homes off the gas grid, applications properly made 21 July 2026 to 31 March 2027
Home Energy Scotland	grant up to £7,500 (+£1,500 eligible rural and island homes), interest-free loan up to £7,500	Scotland, 2026/27, budget-limited
VAT on installed heat pumps	0%, then 5%	0% until 31 March 2027
New gas boiler, government estimate	about £3,500, VAT included	DESNZ, Boiler Upgrade Scheme business case 2026
Electricity unit rate	26.32p/kWh	price cap, GB average, direct debit, 1 October to 31 December 2026, no VAT in Great Britain
Gas unit rate	7.97p/kWh	same period, 5% VAT included

How we worked this out

Our figures use our example home (1970s gas semi, 97 m², 9,500 kWh of gas, 85% efficiency for its existing boiler as our assumption), the median price for grants paid July–September 2026, the October–December 2026 cap rates and SCOP 2.5 / 2.8 / 3.1; standing charges, servicing and finance are left out. More in our editorial method.

Frequently asked questions

Is a heat pump electric or gas?

Electric. It uses electricity to run a compressor and fan and takes the rest of its heat from the outside air, so it needs no gas supply. If you claim the Boiler Upgrade Scheme in England and Wales, ask your installer whether you can keep gas for cooking.

Is an air source heat pump the same as air conditioning?

No. In the UK an air source heat pump heats water for your radiators, underfloor heating and taps. Units that blow warm air into rooms are air-to-air heat pumps, which work much like air-conditioning units and don't heat water; see air-to-air heat pumps.

Can an air source heat pump cool my house?

Some can, by running the refrigerant cycle in reverse: Mitsubishi Electric's service manual for its Ecodan R290 outdoor units, for example, gives operating ranges for both heating and cooling. It depends on the model and how the system is set up, so ask for cooling in the quote if you want it. In England, permitted development doesn't cover a heat pump used solely for cooling.

Do I need planning permission for an air source heat pump?

Usually not for a house in England or Wales, if the unit passes the MCS 020(a) noise calculation and meets the size and siting conditions. Permitted development doesn't cover listed buildings, conservation areas restrict where the unit goes, and Scotland and Northern Ireland have their own rules, so check with your local planning authority.