Running air conditioning is far cheaper than most people expect. A modern 2.5kW inverter unit cooling a bedroom typically costs around 10–20p per hour to run once the room is up to temperature — because after the initial cool-down, an inverter unit draws only a fraction of its rated power to hold the temperature steady.
What determines the running cost?
Four things drive what you’ll actually pay:
- Unit size (kW output). A bigger unit cooling a bigger space uses more power.
- Efficiency rating. SEER measures cooling efficiency (aim for 7+, i.e. A++) and SCOP measures heating efficiency (aim for 4+). Higher is cheaper to run.
- Inverter vs on/off. Inverter compressors modulate their output to hold a steady temperature instead of blasting at full power and cycling on and off — the single biggest saving.
- How you use it. Cooling one room for a few hours costs pennies; running several units all day costs more.
Electricity prices come from the regulator’s cap — you can check the current rate on the Ofgem energy price cap unit rates page. The figures below use roughly 26p per kWh (the July–September 2026 cap).
| Unit / room | Rough running cost | Per 8-hour night/day |
|---|---|---|
| 2.5kW — bedroom | ~11–20p per hour | ~£0.90–£1.60 |
| 3.5kW — living room | ~20–32p per hour | ~£1.60–£2.60 |
| 5.0kW — open-plan space | ~34–52p per hour | ~£2.70–£4.20 |
Heating mode is even more efficient
In winter, the same unit works as a heat pump and can be one of the cheapest ways to warm a single room. Because it moves heat rather than generating it, a unit with a SCOP of 4 delivers about four times more heat than the electricity it uses — often cheaper per unit of heat than a plug-in electric heater. We explain this in detail in does air conditioning heat your home too?
How to keep running costs down
- Choose a correctly sized, high-efficiency inverter unit — see what size air conditioning unit you need.
- Set a sensible target temperature (around 24°C for cooling) rather than the coldest setting.
- Close windows and blinds on the sunny side while it runs.
- Use the timer and eco/sleep modes so it isn’t cooling an empty room.
- Keep filters clean — a clogged filter makes the unit work harder.
Want an efficient system that’s cheap to run?
We fit quiet, A++ inverter air conditioning across Sheffield & South Yorkshire.
Call 07534 793949 or see air conditioning installation in Sheffield.
Frequently asked questions
Is air conditioning expensive to run?
Not for most homes. A modern inverter bedroom unit costs roughly 11–20p an hour once the room is cool. Larger units and all-day use cost more, but efficient systems keep bills modest.
How much does it cost to run overnight?
A 2.5kW bedroom unit run for around eight hours typically costs about £0.90–£1.60, depending on the weather and your electricity rate.
Is it cheaper than a portable air conditioner?
Usually yes. Fixed inverter split systems are considerably more efficient than portable units, which draw more power for the same cooling.
Does an inverter unit really save money?
Yes. Inverter models modulate their output to hold temperature instead of running at full power and cycling on and off, which noticeably lowers running costs.
Running costs are estimates based on a c.26p/kWh electricity rate (July–September 2026 price cap) and vary with your tariff, weather, unit and usage.