Most people shopping for air conditioning believe they are buying a cooling machine. What they are almost always buying, whether the brochure says so or not, is a heat pump. Nearly every split system sold for homes in the UK is an air-to-air heat pump, and the same box that cools your living room in July will heat it in January if you press a different button on the remote.
The same machine, run in reverse
An air conditioner works by moving heat from inside the house to the outside. A reversing valve lets it run the other way, gathering warmth from the outdoor air, even cold outdoor air, and releasing it indoors. Because the machine is moving heat rather than generating it, each unit of electricity it consumes typically delivers several units of heat into the room. A plain electric heater can never do better than one for one. That gap is the whole running-costs argument, and it is why the heating side of these systems deserves more attention than it gets.
Where the running-costs logic lands
Against electric radiators, panel heaters or a fan heater in the home office, the air-to-air heat pump wins comfortably, delivering the same warmth for a fraction of the electricity. Against mains gas the sums are tighter, because gas is cheap per unit, but the heat pump has a habit of winning in the rooms gas serves badly: the converted loft, the garden office, the extension the radiators never quite reach. Heating one occupied room with a heat pump instead of firing the whole boiler for it is where owners tend to notice the difference on the bill.
What it will not do
An air-to-air system heats air, and only air. It will not warm your radiators or your hot water tank, so it does not replace a boiler in the way an air-to-water heat pump aims to. Think of it instead as precise, inexpensive heating for the rooms you live in most, layered on top of whatever heats the rest of the house. Owners in the shoulder months of spring and autumn often find the heat pump covers the house alone, and the boiler stays off for weeks longer than it used to.
The question to ask at the survey
When quotes arrive, ask each installer for the unit's heating capacity at a low outdoor temperature, not just the headline cooling figure, and ask which models hold their output best in a cold snap. It is one question, it takes a minute, and it sorts the firms who understand heat pumps from the ones who only sell cooling. Among the 996 air conditioning companies listed here, plenty talk about heating as readily as cooling, and their listings show it. Compare companies near you, or describe the rooms you want to heat and cool and gather quotes. Then check what you currently spend heating the one room you use most. That figure is the benchmark your new system has to beat, and it usually does.
