What Does It Cost to Run Air Conditioning?

Less than most people assume, and the reason is efficiency rather than optimism.

The principle

A modern wall-mounted system doesn't generate heat or cold. It moves it. That means each unit of electricity you put in shifts several units of heat, which is why these systems run so much more cheaply than direct electric heating or old-fashioned portable air conditioners.

Portable units are the comparison most people have in their heads, and they're the worst possible benchmark. A portable unit vents hot air through a hose in a partly open window, which pulls warm air back into the room the whole time it runs. A properly installed fixed system doesn't have that problem, and uses far less electricity for a much better result.

What actually drives your bill

How long it runs. A modern inverter system works hardest when it starts, then throttles back to maintain the temperature. Long, steady running at a sensible setting is cheaper than repeatedly blasting a room cold and switching off.

The temperature you set. Every degree matters. Setting 24°C rather than 19°C in summer, or 20°C rather than 24°C in winter, makes a substantial difference over a season.

How well the room holds temperature. An uninsulated conservatory with single glazing will cost more to keep comfortable than a well-insulated bedroom. The system can only do so much about a room that leaks.

Whether it's serviced. A clogged filter or a dirty coil makes the system work harder for the same result. This is the running cost people forget.

Summer versus winter

Summer use in the UK is genuinely occasional — a few weeks of real demand, and hours rather than days at a time. For most households the summer cost is smaller than expected simply because the running hours are low.

Winter is where the numbers get interesting, because you're comparing against your existing heating. Heating one room with a heat pump, rather than firing the whole central heating system to warm a home office, is often the cheaper option — and it's a genuine saving rather than an additional cost.

That's the framing most people miss. Judged as a summer luxury it looks like an expense. Judged as year-round room heating, it can pay for part of itself.

Getting the best from it

• Set it and leave it, rather than switching on and off
• Use a moderate temperature rather than an extreme one
• Keep doors closed in the room you're conditioning
• Close blinds or curtains on sun-facing windows in summer
• Keep filters clean and have it serviced annually