Heat pump vs air conditioning: what's the difference?

Air conditioning is a heat pump

Every heat pump, and every air conditioner, works the same way. A refrigerant circuit and a compressor move heat from one place to another. An air conditioner that only cools moves heat out of your room. A heat pump moves heat in. Most split systems sold for homes today do both: a reversing valve switches the direction, so the same unit cools in summer and heats in winter.

That makes a heating-capable split system an air-to-air heat pump. It takes heat from the outside air and delivers it into the room as warm air. Planning law in England calls it an air source heat pump, and the government's Boiler Upgrade Scheme lists air-to-air as its own type of heat pump.

Air to air vs air to water heat pump

Both take heat from the outside air. The difference is what they put it into.

An air-to-air heat pump puts heat into the air of a room through an indoor unit on the wall or floor, or a ducted system in the ceiling. It heats and cools, room by room, but it doesn't touch your radiators or hot water.

An air-to-water heat pump puts heat into water. That water runs through radiators or underfloor heating, and through a hot water cylinder for your taps and showers. It replaces a boiler completely. It runs best at lower water temperatures than most boilers, so some radiators may need to be bigger. It usually doesn't cool through standard radiators.

Heat pump vs air conditioner: side by side

Air-to-water costs are government Boiler Upgrade Scheme statistics: what MCS installers reported for a median 8 kW system, including VAT and the grant value. Air-to-air costs are our own starting prices.

Heat pump vs air conditioner cost

To fit, air-to-air costs far less for a few rooms. Our starting prices run from £1,850 for one bedroom unit to £6,500 for four rooms on one outdoor unit, including VAT. The government's Boiler Upgrade Scheme statistics put the median air-to-water install at £12,908 for April to June 2026, before taking off the £7,500 grant.

Those two figures don't buy the same thing. Air-to-water heats the whole house and your hot water. Four air-to-air rooms heat and cool four rooms. For a fair comparison, price what you actually need heated, cooled and supplied with hot water.

Running costs: what each kWh of heat costs

Both run on electricity, so the cost of heat depends on efficiency (SCOP). Prices are the Ofgem cap for 1 October to 31 December 2026: 26.32p per kWh of electricity, 7.97p per kWh of gas.

Workings: 26.32p ÷ SCOP, and 7.97p ÷ 0.9 for gas. Air-to-air SCOPs are from Daikin and Panasonic spec sheets. Air-to-water efficiency depends heavily on the design and the water temperature, so ask your installer for the figure for your home.

Reading the running costs fairly

Air-to-air and air-to-water SCOPs are measured under different test conditions, so don't compare the numbers directly. An air-to-water heat pump heats water for radiators and taps, and the hotter the water it has to make, the lower its efficiency. The Boiler Upgrade Scheme rules require an air-to-water heat pump to have a SCOP of at least 2.8.

Either way, a well-designed heat pump costs less per kWh of heat than plug-in electric heating by a wide margin. Against gas, the result depends on the efficiency your system really achieves. Our running costs guide has the full workings for 2.5, 3.5 and 5 kW air-to-air units.

Choose air-to-air if

• You want cooling in summer as well as heating in winter
• You're heating particular rooms: a loft, extension, conservatory, garden room or home office
• You have electric panel or storage heaters and want lower bills
• You live in a flat with no space for a hot water cylinder
• You want each room controlled on its own
• You're happy to keep your boiler, cylinder or immersion for hot water

Choose air-to-water if

• You want to replace your boiler completely, hot water included
• You want to keep heating through radiators or underfloor heating
• You have room inside for a hot water cylinder and outside for the outdoor unit
• You want the £7,500 grant, which needs an MCS-certified installer
• You don't need cooling

Using both together

Some homes have an air-to-water heat pump for heating and hot water, and add air conditioning to the rooms that overheat in summer, often bedrooms and lofts. Others keep a gas boiler and add air-to-air for cooling and to heat the rooms the boiler struggles with.

Planning is the thing to check. Under Class G, a semi-detached or terraced house can have only one heat pump as permitted development, and a detached house two. If you already have an air-to-water heat pump on a semi or terrace, adding an air conditioning outdoor unit means a second heat pump, which needs planning permission. A multi-split, with several rooms on one outdoor unit, keeps the count down.

Grants: £7,500 and £2,500

The Boiler Upgrade Scheme in England and Wales gives £7,500 towards an air-to-water heat pump. Until March 2027, homes heated by oil or LPG with no mains gas connection can get an extra £1,500. The installer must be MCS certified and applies for you. You can't get a grant for a hybrid system that keeps a boiler for heating.

Since 28 April 2026 the scheme has also included £2,500 towards an air-to-air heat pump, but it can't be claimed yet. No installer can be MCS certified for air-to-air until the certification bodies are accredited, and government statistics show 145 applications by the end of August 2026 and no vouchers issued. When it opens it will need the system to heat the whole home and replace existing fossil fuel or electric heating.

Planning: the same rules for both

In England both are air source heat pumps under Class G of the permitted development rules. The outdoor unit must be no bigger than 1.5 m³ on a house, meet the MCS 020(a) noise limit of 37 dB(A) at neighbours' windows, and stay off pitched roofs and walls facing a highway in conservation areas. For air conditioning there's one extra rule: since 29 May 2025, a unit that only cools isn't covered. Our planning permission guide has every rule.

What air-to-air costs with us

Every home system on this list heats and cools. Prices include VAT. A free survey confirms the size and price.

• A bedroom or study

  2.5 kW wall unit, 5 m pipe, fitted in a day

  from£1,850inc. VAT

• A living room

  3.5 kW wall unit

  from£2,050inc. VAT

• Open plan or a loft

  5 kW wall unit

  from£2,450inc. VAT

• Two rooms, one outdoor unit

  Multi-split

  from£3,650inc. VAT

• Three rooms

  Multi-split

  from£5,100inc. VAT

• Four rooms

  Multi-split

  from£6,500inc. VAT

Heat pump or air conditioning: questions