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Comparison

Air-to-Air vs Air-to-Water Heat Pumps: Which Is Right for You?

Air conditioning, which heats and cools room by room, against an air-to-water heat pump that replaces your boiler

10 min read•Updated October 2026
Air conditioning indoor wall unit in a modern living room

Both take heat from the outdoor air. What they do with it is different. An air-to-air heat pump is air conditioning: indoor units blow warm air into the rooms they are in, and the same system cools in summer. An air-to-water heat pump heats water instead, for your radiators or underfloor heating and your hot water taps, so it takes the place of a boiler.

We fit air conditioning, the air-to-air kind: wall-mounted split, multi-split, ceiling cassette and ducted. We don’t fit air-to-water systems; those are a job for a specialist heating installer. This guide sets out the differences so you can tell which one you are after.

At a glance

Air-to-air and air-to-water heat pumps compared
Air-to-air (air conditioning) Air-to-water
Heats with Warm air from an indoor unit in each room Hot water through radiators or underfloor heating
Cooling YesNot through radiators
Hot water for taps and showers No: you keep what you have Yes, usually stored in a cylinder
Your boiler Stays, if you have oneUsually replaced
Who fits it An F-gas certified air conditioning installer, like us A specialist heating installer
Suits Heating and cooling the rooms you use most Replacing the boiler for the whole house

Air-to-air: air conditioning

How it works

An outdoor unit gathers heat from the outside air, and pipework carries it to indoor units, usually wall-mounted, that blow warm air into the room. Run the other way, the same system cools. It is the air conditioning you may know from offices and hotels, and GOV.UK notes that most air-to-air systems can both heat and cool. For the cycle step by step, see how air-to-air heat pumps work.

Good points

  • •
    Heating and cooling: one system does both, so there is nothing extra to buy for summer.
  • •
    Less building work: no new radiators, cylinder or plumbing; your existing heating stays as it is.
  • •
    Quick to warm a room: warm air reaches you within minutes.
  • •
    Room by room: each indoor unit has its own temperature, so you can heat or cool just the rooms you are using.
  • •
    Drier air: it takes moisture out when cooling, or in dry mode, which helps in a damp Manchester summer.

Drawbacks

  • •
    No hot water: it heats rooms, not water, so you keep your boiler, cylinder or immersion heater for taps and showers.
  • •
    Only rooms with a unit: rooms without an indoor unit are not heated by it.
  • •
    Visible indoor units: a wall-mounted unit is on show, though ceiling cassettes and ducted systems hide most of it.
  • •
    Air movement: some people notice the airflow and prefer the gentler warmth of a radiator.

Air-to-water: a boiler replacement

How it works

An air-to-water heat pump heats water, which is pumped round radiators or underfloor heating as a boiler’s would be. It takes its heat from the outdoor air rather than from burning gas, and it can heat your hot water too, usually stored in a cylinder.

Good points

  • •
    Heating and hot water: one system for the whole house, as a boiler is.
  • •
    Uses radiators: in some homes the existing radiators can stay; in others some need to be larger.
  • •
    Radiator warmth: many people prefer the steady warmth of radiators or underfloor heating.
  • •
    Nothing on the walls: no indoor units in the rooms.

Drawbacks

  • •
    No cooling through radiators: for summer you would need air conditioning as well.
  • •
    Slower to warm up: it runs radiators cooler than a boiler, so it suits steady, longer heating rather than quick bursts.
  • •
    More work to fit: usually a hot water cylinder, sometimes a buffer tank, depending on the design, and in some homes larger radiators or new pipework.
  • •
    Insulation matters: a poorly insulated home may need improving first.

Running costs

Both move heat rather than make it, so both give more heat than the electricity they use. The air conditioning we fit is typically rated at a seasonal heating efficiency of 400% or more (SCOP 4 or more). That is a lab figure over a standard season; on the coldest UK days real output is lower, so for costs we use GOV.UK’s figure for air-to-air systems, about three units of heat for every unit of electricity. At the Ofgem price cap for 1 October to 31 December 2026, paying by direct debit, as a Great Britain average, electricity is 26.32p per kWh (with no VAT on electricity from 1 October 2026 to 31 March 2027), so a kWh of heat from air conditioning costs about 8.8p.

That is about the same as heat from a gas boiler (7.97p per kWh of gas, including 5% VAT, through a boiler about 90% efficient: about 8.9p), and about a third of the cost of heat from a plug-in electric heater (26.3p). For a fuller comparison, see gas boiler vs electric heating vs air conditioning.

An air-to-water system’s figure depends on how hot its radiators have to run and on heating your hot water, so it varies from home to home; a heating installer’s design for your house will give one.

Which is right for you?

Air conditioning (air-to-air), if:

  • You want heating and cooling from one system
  • You want to heat and cool the rooms you use most, such as bedrooms
  • You want to keep your existing boiler and radiators
  • You want a room to warm up quickly
  • You are happy with indoor units on show

Air-to-water, if:

  • You are replacing your boiler and want one system for heating and hot water
  • You prefer warmth from radiators or underfloor heating
  • You are planning a major renovation or building new
  • You don’t need cooling, or will add air conditioning for it
  • You want nothing on the walls

For air-to-water, talk to a specialist heating installer: we fit air conditioning only.

Manchester homes

Weather

  • •
    Cold spells: both give less heat for each unit of electricity as it gets colder, so either should be sized for a cold day in your home, not an average one.
  • •
    Warmer summers: 2025 was the UK’s warmest summer on record, which makes cooling worth more than it used to be.
  • •
    Damp: air conditioning’s dry mode takes moisture out of a room that feels clammy.

Property types

  • •
    Victorian and Edwardian terraces: air conditioning can often be fitted without disturbing period features.
  • •
    Modern semis and detached houses: either can work; it comes down to whether you want whole-house heating and hot water, or heating and cooling room by room.
  • •
    Flats and apartments: air conditioning is often more practical, with less work inside and a temperature for each room. Check the lease and the building’s rules for an outdoor unit first.

Can you have both?

Yes. Some homes have an air-to-water heat pump for heating and hot water, then add air conditioning in the rooms that get too warm in summer, such as bedrooms and a home office. That gives you:

  • ✓
    Whole-house heating and hot water
  • ✓
    Cooling where you need it
  • ✓
    Quick heat in those rooms on a cold evening

The two are separate systems, fitted by different trades: the air-to-water heat pump by a heating installer, and the air conditioning by an installer like us.

Sources

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