The short answer
About 15–25p per hour for a typical 2.5 kW split. That unit draws roughly 0.6–1.0 kWh per hour, and at a unit rate of around 25p/kWh the arithmetic gives 15–25p. Bigger or less-efficient units cost more per hour; a higher energy-rating model costs less. The figure also rises on very hot or very cold days because the unit has to work harder.
The per-hour cost is the simplest way to think about air conditioning, because it lets you scale to any run time. It is just power drawn multiplied by your unit rate. This page shows that single calculation, then explains the factors that nudge the figure up or down so you can estimate your own cost confidently.
Per-hour cost at a glance
- 2.5 kW split ~15–25p per hour
- Power drawn ~0.6–1.0 kWh/hour
- Unit rate used ~25p/kWh (Ofgem)
- Hotter days Higher draw, higher cost
- Efficient model Lower cost per hour
The one calculation you need
Cost per hour is power drawn multiplied by your unit rate. Nothing more. For a typical 2.5 kW split it comes out like this:
- Low end: 0.6 kWh × 25p = 15p per hour
- High end: 1.0 kWh × 25p = 25p per hour
Because it is a per-hour figure, you can scale it to any run time: two hours is 30–50p, four hours is 60p–£1.00, eight hours is £1.20–£2.00. The two inputs are the unit’s power draw (from its data sheet, in kWh per hour) and your unit rate (from your Ofgem-regulated tariff). Get those two numbers and the rest is multiplication. Remember to use the power input, not the cooling capacity in kW — the capacity is the heat moved, not the electricity consumed.
What moves the figure
The per-hour cost is not fixed even for one unit. It rises when the outside temperature is extreme, because the unit works harder to reject (or in heating mode, gather) heat. It rises for larger-capacity units, which draw more power. It falls for higher energy-rating models, which do the same cooling for less electricity. And it scales directly with your unit rate, so a cheaper tariff lowers every hour proportionally. The table below shows how the same draw lands at two different rates.
| Power drawn | Cost at 25p/kWh | Cost at 30p/kWh |
|---|---|---|
| 0.6 kWh/hr | 15p | 18p |
| 0.8 kWh/hr | 20p | 24p |
| 1.0 kWh/hr | 25p | 30p |
Portables and bigger units
A self-contained portable is generally less efficient than a fixed split, so its per-hour cost for the same cooling is usually higher even though it is cheaper to buy. A larger split — say 3.5 kW or 5 kW — draws more power and therefore costs more per hour, though it cools a bigger room faster and may run for fewer hours overall. Always work from the unit’s own power input rather than assuming the 2.5 kW figures, because a wrongly-sized unit can cost far more per hour than necessary. For sizing, see what size air con do I need.
- Portable — convenient but higher per-hour cost.
- Larger split — more power drawn, higher per-hour cost.
- Efficient inverter — lowest per-hour cost for its size.
Scaling to a day, week or season
Once you have the per-hour cost, the rest is multiplication: hours per day for a daily figure, then days for a weekly or seasonal total. That makes the per-hour number the most useful one to know, because everything else is built on it. For instance, four hours a day across a thirty-day hot spell at 20p per hour is roughly £24 for the month — modest for the comfort it buys. For the daily and seasonal view see running cost and the underlying kWh in electricity usage.
Why the per-hour figure is the one to trust
Headline claims about air conditioning “costing pennies” or “costing a fortune” are usually meaningless because they hide the run time. The per-hour figure cuts through that: it pins down the only two variables that matter — how much power the unit draws and what you pay per unit — and lets you decide for yourself how many hours you want to run it. A household that needs two hours of cooling before bed is in a completely different position from one cooling a home office for ten hours a day, yet both can plan accurately from the same per-hour number. It also makes tariff changes easy to absorb: if your unit rate rises, you simply re-multiply, and you instantly see the new per-hour cost without re-doing the whole calculation. Keep the per-hour figure in mind and no electricity bill involving air conditioning should ever catch you out.
These are typical 2026 estimates for guidance only; your real cost depends on your unit and tariff.
Know your per-hour number
Take your unit’s power draw, multiply by your unit rate, and you have a figure you can scale to any run time.
Frequently asked questions
How much is air con per hour in the UK?
About 15–25p per hour for a typical 2.5 kW split, based on it drawing 0.6–1.0 kWh and a unit rate of around 25p/kWh.
Does a bigger unit cost more per hour?
Yes. A larger-capacity unit draws more electrical power, so its per-hour cost is higher, although it cools a bigger room more quickly.
Why does the per-hour cost change with the weather?
On very hot or very cold days the unit works harder to move heat, so it draws more power per hour and the cost rises.
How do I get an exact per-hour figure?
Multiply your unit’s power draw (kWh per hour, from the data sheet) by your current unit rate from your bill. That gives the precise per-hour cost for your situation.
Sources & further reading
- Ofgem — typical domestic electricity unit rates
- Manufacturer technical data (e.g. Daikin, Mitsubishi Electric) — power input specifications
- Energy Saving Trust — running cost and efficiency guidance
- gov.uk — household energy efficiency information
This guide is general information, not a site-specific survey or a substitute for a quote from an F-Gas-certified installer. Installation, servicing and refrigerant handling are legally restricted to F-Gas-certified engineers.