Air conditioning vs heat pump: same kit, different job

Most UK air conditioners are heat pumps: if a unit can heat as well as cool, it is an air-to-air heat pump. HMRC, Which? and the Energy Saving Trust all say so in their own words. The choice that matters is air-to-air (blown air, from about £1,900 for a room) against air-to-water (radiators and hot water, about £12,000). This guide compares air conditioning vs heat pump on cost, running cost, grants, planning and fit.

Quick answer: For one room or a few rooms cooled in summer and warmed in winter, a reversible split is the usual answer. To heat the whole house through radiators and make hot water, you need an air-to-water heat pump, a bigger and dearer job.

Last checked 10 October 2026. Prices, grant status and the energy price cap change, so confirm them on your own quote.

1. A reversible air conditioner and an air-to-air heat pump are the same hardware.
2. Air-to-air costs about £1,900 for a room and £3,700 for a three-bed semi. Air-to-water costs about £12,000 (Energy Saving Trust).
3. The £2,500 air-to-air grant is in law but nobody can claim it yet, and it would not cover a one-room unit.
4. Cooling-only units need planning permission. Heating-capable ones can be permitted development.
5. Ask for the F gas certificate number and the VAT rate in writing before you sign.

The short answer: is air conditioning a heat pump?

Yes, in most cases. A reversible air conditioner moves heat in both directions, which is what a heat pump does.

What the official sources say

Which? says: "In theory, there is little difference between an air conditioning system and an air-to-air heat pump." The same article (updated 17 July 2026) adds that a reversible unit can heat or cool, but not all units are reversible.

HMRC's VAT notice 708/6 says: "HMRC's understanding is that most air conditioning units are air source heat pumps." It adds that in cases of doubt it depends on the facts of each case. The Energy Saving Trust, on a page updated 11 September 2026, says air-to-air heat pumps are "sometimes referred to as air conditioning". Our air-to-air heat pump guide covers the same ground in more detail.

What Sussex installers call it

Installers sell the same kit under both names. Ernest Air Cooling in Shoreham-by-Sea says its systems are "reverse-cycle heat pumps". Eaglereach Mechanical in Hove lists air-to-air heat pumps "that cool in summer and heat in winter, all from the same indoor unit". Of the 39 installers we list, 11 record an air-to-air service (read 10 October 2026). Naming these firms is not a recommendation; it shows how the trade uses the words.

The one thing that is not a heat pump

A cooling-only unit. It has no reversing valve, so it cannot heat. MCS, the scheme that certifies heat pump installers, says "systems that only provide cooling are excluded from the MCS Scheme". Portable units sit outside this comparison. HMRC's notice says only permanently fixed air source heat pumps qualify for its VAT relief, not portable ones.

Air conditioning vs heat pump at a glance

Sources: Energy Saving Trust (11 and 23 September 2026), Ofgem, MCS, Which?, Planning Portal, all read 10 October 2026. The cost gap between cooling-only and reversible splits is small, but we found no sourced figure for it, so we give none.

How air conditioning heats, and what a heat pump is

A heat pump moves heat, it does not make it

A refrigerant circulates between an outdoor unit and an indoor unit. In cooling mode it carries heat out of the room. A reversing valve flips the direction in heating mode, so it carries heat in from outdoor air, even cold air. That is why the electricity drawn is smaller than the heat delivered. Eurovent-certified test data for one 3.5 kW Daikin unit shows 3.50 kW of cooling for 0.76 kW of electrical input. The rated kW is heat moved, not power drawn.

Air-to-air: the same kit as air conditioning

The indoor unit blows warm or cool air straight into the room. Which? says one outdoor unit can connect to up to five indoor units. For the single-room version, see our guide to split system air conditioning.

Air-to-water and ground source

An air-to-water heat pump uses the same outdoor heat but delivers it to water, which feeds radiators, underfloor pipes and a hot water cylinder. Ground source, which takes heat from buried pipes, is outside this guide.

Air-to-air vs air-to-water heat pump: the differences that matter

Cost to buy and install

The Energy Saving Trust puts air-to-air at about £1,900 for one room and about £3,700 for a three-bed semi-detached house. For air-to-water it gives a typical £12,000 before any grant. Three price guides we read give £1,500 to £3,500 for one installed room: Trade2Base £1,800 to £3,500, Heatable £2,000 to £3,500 and Airtasker £1,500 to £3,000. Two Sussex installers publish single-room prices of £1,350 to £2,500 (Eaglereach) and £1,899 to £2,500 (Ernest). All were checked on 10 October 2026. These are published prices, not quotes. Our air conditioning cost guide sets out the full ranges, including multi-split and ducted.

Cost to run: October to December 2026

Ofgem's cap from 1 October to 31 December 2026 is 26.32p per kWh for electricity and 7.97p per kWh for gas. The Energy Saving Trust says there is "currently not much data on how air-to-air systems perform in the UK", and we found no peer-reviewed UK field trial. So the table below is our arithmetic on cap prices, not a forecast of your bill.

Our arithmetic from Ofgem's cap rates (standing charges excluded). The 90% boiler efficiency is our assumption for a modern condensing boiler; an older boiler will do worse.

A heat pump breaks even with gas at a SCOP of about 3. Electricity costs about 3.3 times as much as gas per kWh at this cap, which is why a bill can rise if a heat pump replaces gas and performs poorly. Which? says air-to-air heat pumps are "much more efficient to run than a direct electric heating system".

For a real unit, Eurovent-certified lab data for a Daikin RXM35A with FTXM35A shows 4.00 kW of heat for 0.88 kW of input (COP 4.55) at standard conditions, and a SCOP of 5.20. At 26.32p, 0.88 kW costs about 23p an hour at full load. That is lab data, not a home result. At minus 10C the same certificate lists a COP of 3.15, so output per unit of electricity falls as it gets colder. Our running costs guide and the running costs calculator let you test your own numbers.

Hot water and radiators

Most air-to-air systems do not make hot water, says the Energy Saving Trust. MCS says the same. Some can connect to a hot water tank, according to Which?, but not all do. Heating water with an immersion heater gives about 1 kWh of heat per kWh of electricity, which is 26.3p per kWh at the cap, so hot water can narrow the running cost gap between the two heat pump types. Air-to-water suits a house that already has radiators. If you have none, air-to-air avoids the work of fitting any.

Comfort, noise and cooling

The Energy Saving Trust says "indoor units can be noisier than other heat pumps" and that air-to-air recirculates room air, so you still need to ventilate. Daikin's product profile lists its smallest Perfera indoor unit at 19, 25 and 41 dBA on silent, low and high in cooling mode. Check the figures for the model you are quoted.

Cooling is where air-to-water is weaker. Which? says only some air-to-water heat pumps can cool. The National Energy Foundation, a registered charity, says cooling through radiators can cause condensation and is slow to bring a room down. It dates that page July 2025.

Which?, the Energy Saving Trust and the Energy and Climate Intelligence Unit all put passive measures such as shading first. Which? also warns that using a heat pump for cooling when you had none "will considerably add to your annual energy usage".

Sizing: ask for a heat loss figure, not just a cooling load

Cooling load and heat loss are different numbers. One homeowner in a YouTube account described having about 18 kW of heat output installed against a house heat loss of about 7 kW, with the units cycling in mild months. That is one account, not a finding. MCS has published a new methodology and tool aimed at air-to-air heat pumps (MCS 031 b). Ask the installer how they sized the unit and for the heat loss figure. Our BTU calculator gives a starting point for a single room.

The £2,500 grant: where it stands on 10 October 2026

What is on the books

The Boiler Upgrade Scheme in England and Wales lists "£2,500 off the cost and installation of air-to-air heat pumps for residential properties only" on Ofgem's page. Air-to-water and ground source are £7,500, or £9,000 in eligible off-gas-grid properties until 31 March 2027. The regulations for air-to-air came into force on 28 April 2026, and the scheme is extended to 2030 (Ofgem installer guidance V5, MCS).

Why you cannot claim it yet

MCS's consumer page, read 10 October 2026, says: "At the moment, no installers are yet certified to install air-to-air heat pumps." MCS says installers can only extend their scope once certification bodies have UKAS accreditation. The Energy Saving Trust, updated 11 September 2026, says "Not yet, but there will be." The Energy and Climate Intelligence Unit reported on 10 July 2026 that 45 air-to-air heat pumps were supported under the scheme in May and that no installations had taken place. We found no start date. Do not sign on the strength of a grant until the installer shows written proof of certification.

Why a one-room split would not qualify anyway

MCS says air-to-air systems must be "optimised to provide heating to your whole property". Ofgem's guidance says the grant-funded heat pump must have "sufficient kilowatt thermal capacity to meet the full space heating demands of a property on its own". It must replace a fossil fuel system or an electric heating system without a heat pump. Hybrids with a boiler are not eligible, and Which? says you cannot use the grant to add one alongside a gas or oil boiler. So a bedroom unit gets nothing. Our air-to-air heat pump grant guide tracks the status.

Planning, F gas and VAT: three checks before you sign

This is general information for England. Check with your council or a solicitor for your own case.

Planning

The Planning Portal says permitted development rights for air source heat pumps apply only if the system has a heating function. If a unit only cools, "an application for planning permission will be required". A 2025 order (SI 2025/560, in force 29 May 2025) added the condition that the unit is not used solely for cooling. Other limits include an outdoor unit volume of no more than 1.5 cubic metres on a house or 0.6 on a block of flats, no pitched roof, and no wall or roof fronting a highway in a conservation area. The noise limit is 37 dB LAeq,5mins under MCS 020 a). Listed buildings are excluded.

Brighton and Hove City Council says where permission is required, an air source heat pump is acceptable in heritage terms with a large front garden and little visibility, and "unlikely to be acceptable" for terraces with small front gardens where the equipment is prominent from the road. See our Brighton and Hove planning guide.

F gas

A company, including a sole trader, must be certified by an approved body to install or service stationary air conditioning for others. Approved bodies are REFCOM, the F-Gas Register (Quidos) and Bureau Veritas. Each engineer needs a personal qualification too. Working without it is against the law, according to GOV.UK. Of the 39 Sussex installers we list, 38 were found on a public F gas register on 10 October 2026. Registers have gaps, so "not found" does not mean "not certified". Our F gas register guide shows how to search. For the grant, the MCS technical supervisor on an air-to-air job must hold refrigeration, air conditioning and heat pump competence at Level 3 or above (MCS, 13 April 2026).

Seven listed firms claim MCS for heat pumps, and none shows a certificate number we could check. Ask for the number.

VAT

HMRC's notice 708/6 gives a zero rate for installing certain energy-saving materials from 1 May 2023 to 31 March 2027, and 5% from 1 April 2027. Fixed air source heat pumps qualify, and HMRC says most air conditioning units are air source heat pumps. Local installer pages disagree: Eaglereach says 0% on qualifying installs, while A J Taylor Electrical in Brighton says 5%. Ask for the VAT rate printed on the quote.

Which should you buy?

The Climate Change Committee said on 20 May 2026 that "we need to plan for more active cooling (such as air conditioning)" because of longer and hotter heatwaves. The table is our reading of the evidence, not a recommendation of any product or installer.

Decision table by situation

Our view

Most readers asking this should buy a reversible split from an F gas certified installer and not wait for the grant. It is the cheaper job, it cools, and it needs no new pipework through the house. If you have working gas radiators, keep the boiler and treat a split as a cooling and single-room heating add-on; the grant will not pay for one beside a boiler. This is our reading of the evidence, not a promise of savings.

Our guide to heating a home with air conditioning covers when a split suits heating, and when it does not.

Next, get three itemised quotes naming the system type, kW rating and pipe run, with the F gas certificate number, VAT rate and any grant claim in writing.

Our heat pump installers page shows what we found for each Brighton and Hove firm, including where we found nothing.

our Brighton and Hove installer directory