The short answer
A typical 2.5 kW split draws roughly 0.6–1.0 kWh of electricity per hour while cooling. Over an eight-hour day that is about 4.8–8.0 kWh. The key is that capacity (kW of heat moved) is not the same as consumption (kWh used): a good inverter unit moves several times more heat than the electricity it draws, which is why its kWh figure is lower than its capacity implies.
Electricity usage is the foundation of every running-cost estimate, so it pays to get the units right. This page separates cooling capacity from electrical consumption, shows how to read your unit’s power input in kWh, and works through realistic daily totals so you can convert usage into pounds using your own tariff.
Electricity usage at a glance
- Power drawn (2.5 kW split) ~0.6–1.0 kWh/hour
- Eight-hour day ~4.8–8.0 kWh
- Capacity vs consumption kW moved ≠ kWh used
- Reading the spec Look for power input (W/kW)
- Cost link kWh × unit rate = cost
Capacity is not consumption
The single most important point is this: a unit’s headline kW is its cooling capacity — the amount of heat it can move out of a room — not the electricity it consumes. A 2.5 kW split moves 2.5 kW of heat but typically draws only 0.6–1.0 kWh per hour of electrical power. That gap is the entire point of a heat pump: it shifts heat from inside to outside rather than generating it, so it delivers far more cooling than the power it uses. Confusing the two is the most common reason people overestimate their bills.
- Capacity (kW) — the heat the unit can move.
- Power input (kW) — the electricity it actually draws.
- Consumption (kWh) — power input multiplied by hours run.
Worked daily totals
To find consumption, multiply the power input by the hours you run the unit. For a 2.5 kW split drawing about 0.8 kWh per hour, the totals look like this:
| Run time | Electricity used | Cost at 25p/kWh |
|---|---|---|
| 1 hour | 0.8 kWh | ~20p |
| 4 hours | 3.2 kWh | ~80p |
| 8 hours | 6.4 kWh | ~£1.60 |
| 12 hours | 9.6 kWh | ~£2.40 |
Use the high end (1.0 kWh/hour) on very hot days when the unit works hardest, and the low end (0.6 kWh/hour) when it is merely holding an already-comfortable room. Your own figure will sit somewhere in that band depending on the weather and how well the room holds its temperature.
Where to find your unit’s figure
Manufacturers publish the power input on the technical data sheet, usually in watts or kilowatts, alongside the energy rating. Treat that as factual specification rather than marketing. A higher energy-rating model has a lower power input for the same cooling, which directly lowers its kWh and therefore your bill, so the rating is worth checking before you buy. If you cannot find the figure, an in-line plug-in energy monitor on a portable, or your smart meter for a fixed unit, will show the real draw. See energy ratings explained and most energy-efficient air con.
- Check the power input (not the capacity) on the data sheet.
- Compare energy ratings between models before buying.
- Multiply power input by your real run hours for the total.
From usage to cost
Once you know the kWh, the cost is simply kWh multiplied by your Ofgem-tariff unit rate. That is the bridge between this page and your bill: total energy used over a period times the rate you pay gives the pounds. Keep the usage down — through correct sizing, an efficient model and sensible run times — and the cost follows. For the cost side see running cost; to drive usage down read the cheapest way to run air con.
Why efficiency ratings move your kWh
Two units with the same 2.5 kW cooling capacity can have noticeably different power inputs, and that difference is exactly what the energy rating captures. A model that does the job for 0.6 kWh per hour rather than 0.9 kWh uses a third less electricity for the same cooling, which over a full summer of regular use is a real saving. This is why the rating is worth more attention than the headline capacity when you buy: capacity tells you whether the unit can cool the room, but the power input tells you what it will cost to do so every hour for the next decade. Inverter-driven units, which modulate their compressor speed rather than cycling fully on and off, tend to post the lowest real-world consumption because they spend most of their time ticking over gently once the room is at temperature, instead of repeatedly drawing the high power of a cold start.
These are typical 2026 figures for guidance. Your actual usage depends on your unit’s power input, the weather and how long you run it.
Turn kWh into your real bill
Find your unit’s power input, multiply by the hours you run it, then by your unit rate — that is your true electricity cost.
Frequently asked questions
How many kWh does air con use per hour?
A typical 2.5 kW split draws roughly 0.6–1.0 kWh per hour. Larger or less-efficient units draw more; check the power input on the data sheet.
Does a 2.5 kW air con use 2.5 kWh per hour?
No. 2.5 kW is the cooling capacity (heat moved), not the electricity used. The unit typically draws only 0.6–1.0 kWh per hour.
How do I work out my daily electricity usage?
Multiply the unit’s power input (kWh per hour) by the hours you run it. Eight hours at 0.8 kWh is 6.4 kWh; multiply by your unit rate for the cost.
Do efficient models really use less electricity?
Yes. A higher energy-rating model has a lower power input for the same cooling, so it consumes fewer kWh and costs less to run.
Sources & further reading
- Manufacturer technical data (e.g. Daikin, Mitsubishi Electric) — power input specifications
- Energy Saving Trust — efficiency and energy-use guidance
- Ofgem — typical domestic electricity unit rates
- gov.uk — energy labelling and 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.