The terms heat pump and air conditioning are used inconsistently in the UK market — sometimes to mean completely different things, sometimes to mean essentially the same thing. This causes genuine confusion when homeowners are trying to work out what they actually need. Here is a clear explanation of how the technologies relate, what the differences are, and which is right for your situation.
The Short Answer
A modern inverter air conditioning system and a modern air source heat pump use identical technology. Both work by moving heat from one place to another using a refrigerant circuit. The difference is primarily in how they are marketed and what they are primarily used for — air conditioning units are marketed as cooling devices that can also heat, while heat pumps are marketed as heating devices that can also cool.
How Both Work
Both systems work on the refrigeration cycle. A compressor pumps refrigerant around a circuit. At one end (the evaporator), the refrigerant absorbs heat from the surrounding air. At the other end (the condenser), it releases that heat. In a fridge, the evaporator is inside the fridge cabinet absorbing heat from the food, and the condenser releases heat into your kitchen (which is why the back of a fridge is warm). In an air conditioning or heat pump system, one heat exchanger is inside the building and one is outside.
In cooling mode: the indoor unit acts as the evaporator (absorbing heat from the room), the outdoor unit acts as the condenser (rejecting heat outside). This cools the room. In heating mode: the process reverses. The outdoor unit absorbs heat from outside air (even in winter down to around -15°C), and the indoor unit rejects that heat into the room. This heats the room.
Where They Differ in Practice
Air Conditioning Units (Split Systems)
Wall-mounted split systems — the Mitsubishi Electric, Daikin, Samsung and LG units that most people picture when they think of air conditioning — are primarily designed for room-by-room climate control. They heat and cool individual rooms or zones. They do not heat water. They are not connected to the central heating circuit or radiators. They provide immediate air temperature control in the rooms where they are installed.
Air Source Heat Pumps (ASHP)
Air source heat pumps marketed as heating replacements — Vaillant, Viessmann, Mitsubishi Ecodan, Daikin Altherma — are designed to replace a gas boiler. They produce hot water that circulates through underfloor heating or radiators (which may need to be upgraded to larger low-temperature radiators for optimal efficiency). They may or may not provide active cooling. They typically heat the whole house through the existing heating distribution system rather than individual rooms.
Which Do You Need?
You want to cool one or more rooms in summer and possibly use them for supplementary heating: A split system air conditioning installation is what you want. Mitsubishi Electric, Daikin, Samsung or LG wall-mounted units installed in the rooms you want to control. This is what AirCon Doctor installs most frequently.
You want to replace your gas boiler with a low-carbon heating system: An air source heat pump (ASHP) connected to your heating circuit is what you want. This is a more complex, more expensive installation typically costing £8,000-16,000, but the £7,500 BUS grant reduces this significantly.
You want both whole-house heating and individual room cooling: Some modern systems — particularly Mitsubishi Ecodan and Daikin Altherma with optional indoor units — can do both. This is a growing category and worth discussing if you are considering a full heating system replacement.
The BUS Grant
The Boiler Upgrade Scheme (BUS) provides a £7,500 grant towards the cost of a qualifying air source heat pump installation. This applies to heat pumps installed as boiler replacements — not to standard domestic air conditioning split systems. The installation must be by an MCS-certified installer. AirCon Doctor hold MCS certification for heat pump installations.
Our Advice
If you primarily want cooling with some supplementary heating benefit, a standard split system air conditioning installation is significantly cheaper (£1,200-5,000 vs £8,000-16,000 for an ASHP), simpler to install, and does not require any changes to your existing heating system. If you are planning to replace your boiler in the next few years and want to move away from gas, an ASHP investigation is worth having.
We install both split systems and qualifying heat pumps. Call 07833 053749 or contact us online for an honest discussion of which is right for your property.