Search for heat pumps and you will find two quite different products described with the same words. One is the wall-mounted split system most people think of as air conditioning. The other is the large outdoor unit that replaces a gas boiler and feeds radiators and a hot water cylinder. Both are heat pumps. What they heat, and how, is where they part company.
Understanding the difference saves a lot of confusion when you are deciding what to put in your home.
Why split air conditioning is a heat pump
Every heat pump moves heat rather than making it. Refrigerant circulates between an indoor and an outdoor unit, absorbing heat in one place and releasing it in another. In cooling mode, heat is taken out of the room and released outside. Reverse the cycle and heat is drawn from the outside air and released into the room, even on a cold day.
Modern split air conditioners are built to run in both directions, which is why they are also called air to air heat pumps or reverse cycle air conditioning. The name describes what goes in and what comes out: heat taken from outside air is delivered as warm or cool air in the room.
Air to air vs air to water at a glance
| Air to air (split air conditioning) | Air to water | |
|---|---|---|
| Delivers heat as | Warm or cool air from an indoor unit | Warm water to radiators or underfloor heating |
| Cooling | Yes | Not in typical UK domestic set-ups |
| Hot water | No | Yes, via a hot water cylinder |
| Replaces the boiler | Usually works alongside it | Designed to replace it |
| Room by room | Yes, one indoor unit per room or zone | Whole-house system |
| Disruption | Indoor unit, outdoor unit and pipe route | Larger outdoor unit, cylinder and often radiator changes |
Which suits which home
An air to air system suits homes that want cooling in summer and efficient heating in particular rooms: a south-facing bedroom, a loft conversion, a conservatory, a garden office or an extension the existing radiators never quite reach. It can go in without touching the boiler or the hot water, so it is a targeted upgrade rather than a change of heating system.
An air to water heat pump suits homeowners who want to replace their gas or oil boiler for the whole house. It typically needs a hot water cylinder, may need larger radiators, and works best in a well-insulated home. It does not normally provide cooling.
Our installations are air to air systems. If cooling, room-by-room comfort and keeping your current boiler matter most to you, that is the route we can help with.
Common mix-ups
- Is a home air conditioner the same as a heat pump?
- A modern split air conditioner that heats as well as cools is an air to air heat pump. Older or cooling-only units, and most portable units, are not designed for heating in the same way.
- Is a portable unit a heat pump?
- Most portable units are designed mainly for cooling and vent heat through a hose. A fixed split system is a different class of equipment.
Questions people ask
Can an air to air heat pump replace my boiler?
Not usually on its own. It heats the rooms it serves but does not heat hot water or feed radiators, so most homes keep the boiler and use the heat pump for specific rooms.
Does an air to air heat pump heat as well as cool?
Yes. The split systems we install are air to air heat pumps, so the same indoor unit cools in summer and heats in winter.
Which is quieter?
Both have an outdoor unit with a fan and compressor. Noise depends on the model, the output and where the outdoor unit is placed, so siting is part of every survey.
Who does the work
- Gas Safe registered engineers — registration 554328
- REFCOM registered for F-Gas refrigerant work
- Worcester Bosch accredited installer
- John The Plumb Ltd, company registration 10026483
Ask what you want the system to do — cool, heat a few rooms, or replace the boiler — and the right kind of heat pump usually becomes obvious.
Talk through an air to air system
REFCOM registered installers fitting Worcester Bosch, Mitsubishi, Daikin, Panasonic and more. Free in-home design and quote.