Many modern split air conditioners are air-to-air heat pumps because they can reverse the refrigeration cycle to provide both cooling and warm air. The useful distinction is therefore often reversible heating and cooling versus cooling-only equipment, not two completely separate technologies. Passive cooling should come first, and any heating claim should be assessed alongside the home's existing system, insulation and hot-water needs.
The terminology in plain English
An air conditioner moves heat from indoors to outdoors when cooling. A reversible air-to-air heat pump can change direction and move heat indoors for space heating. Both commonly use indoor fan units and an outdoor unit linked by refrigerant pipework.
Air-to-air systems heat air rather than water. They do not normally supply domestic hot water and do not directly feed wet radiators. That makes them different from the air-to-water heat pumps often discussed for whole-home heating.
When reversible operation is useful
Reversible operation can suit a garden office, loft room, extension or other zone that needs both summer cooling and responsive winter heating. In a larger home it may complement, rather than automatically replace, the existing heating system.
Ask for a design based on local winter conditions and the actual room heat loss. Rated outputs and seasonal efficiencies are not guarantees of performance in every building, and comfort depends on unit position, airflow, controls and maintenance.
Cooling should follow the hierarchy
London Plan Policy SI 4 asks development to minimise internal heat generation, reduce heat entering the building, manage heat within it and use passive ventilation before relying on active cooling. Existing households can apply the same practical order even when the policy does not directly determine a small installation.
External shading, appropriate glazing treatment, roof insulation, secure ventilation and lower equipment loads can reduce overheating. These steps may allow a smaller system or make active cooling unnecessary for much of the year.
What to check before choosing
Compare the service you actually need: cooling only, zoned heating and cooling, or a broader home-heating replacement. Confirm whether the proposed system can meet the relevant room loads, how condensate will drain and where both indoor and outdoor noise will go.
Planning permission and property consent are separate questions. Check the installation against current planning rules and obtain freeholder, landlord or listed-building advice where relevant. Refrigerant systems must be installed and serviced by competent professionals.
- Confirm whether hot water must be provided by another system.
- Request heating and cooling design loads, not a floor-area guess.
- Review seasonal energy information and controls.
- Check defrost, condensate and cold-weather operation with the installer.
Frequently asked questions
Is every air conditioner an air-to-air heat pump?
No. Cooling-only air conditioners exist. A reversible model that can transfer heat in either direction is commonly described as an air-to-air heat pump.
Can an air-to-air heat pump heat radiators or water?
Normally no. It delivers heated air through indoor units. Domestic hot water and wet radiators usually need a separate solution.
Does reversible heating make cooling free?
No. Cooling and heating both use electricity. The benefit is that one installed system can provide both functions efficiently under suitable conditions.
Is it suitable for a whole London house?
It can be, but that requires a whole-home design covering room heat losses, airflow, indoor-unit locations, hot water and backup needs. A single room installation should not be assumed to replace the full heating system.
Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.