Calculate cooling by the hour and season, then compare the same reversible system with direct electric heating through winter.
Free calculator
Use the electrical input on the unit or product sheet—not the advertised cooling output—to calculate your own hourly, daily and seasonal cost.
Instant result · no email requiredDefault electricity rate: 26.11p/kWh, the Ofgem average Direct Debit cap rate for 1 July–30 September 2026. Standing charges are excluded.
Based on 26.11p/kWh, Ofgem's average Direct Debit electricity cap rate for 1 July to 30 September 2026. Your region, tariff and payment method can differ. Real draw varies with outdoor temperature, insulation and thermostat setting — inverter units throttle down once the room reaches temperature.
| System | Typical draw (cooling) | Cost per hour | 8-hour hot day |
|---|---|---|---|
| Single split, small bedroom (2.0kW) | ~0.6kWh | 15–18p | ~£1.30 |
| Single split, living room (2.5–3.5kW) | ~0.7–1.0kWh | 19–27p | £1.50–£2.20 |
| Multi-split, 3 rooms running | ~1.8–2.4kWh | 49–65p | £3.90–£5.20 |
| Portable unit (for comparison) | ~1.2–1.6kWh | 32–43p | £2.60–£3.50 |
A realistic UK summer — roughly 40 days warranting cooling, 6–8 hours a day — puts a single cooled room at £60–£75 for the whole year's cooling. That's the number to weigh against £1,400–£3,200 installed: running it is not the expensive part. Full install prices in our UK cost guide.
Air to air heat pump running costs depend on electricity price, seasonal efficiency, outdoor temperature and which rooms are heated. Most current fixed split systems heat as well as cool. At a coefficient of performance of 3–4 in suitable conditions, 26.11p of electricity becomes roughly 7–9p per delivered kWh of heat before other losses. That changes the value case entirely:
| Heat source | Effective cost per kWh of heat |
|---|---|
| Electric radiator / panel heater | ~26p |
| Mains gas boiler (incl. efficiency losses) | ~8–10p |
| Air conditioning in heating mode (COP 3–4) | ~7–9p |
Source: Ofgem price-cap unit rates. Standing charges are excluded because the household pays them whether or not the air conditioner runs.
For homes off the gas grid, or rooms heated by plug-in electric heaters—home offices, loft conversions and garden rooms—the winter use can be as important as summer cooling. Run your own SCOP and tariff through the air-to-air heating cost calculator, compare installed prices and current grant rules, then see the wider cheapest way to heat a room and heat pump vs air conditioning trade-off.
The strongest winter opportunity is not a vague national saving claim. It is comparing the same delivered room heat: direct electric at roughly one unit of heat per electricity unit versus a heat pump at a model-specific seasonal COP. Our free calculator shows both costs without asking for an email.
Calculate my heating cost →Size it from a survey, not a guess. An undersized unit runs flat out forever; an oversized one short-cycles. Both burn money. Correct sizing is the single biggest running-cost decision, and it's made on install day.
Set 22–24°C, not 18°C. Every degree lower adds roughly 5–10% to consumption. 23°C in a 32°C heatwave feels glorious.
Keep filters clean. A clogged filter makes the fan work harder for less cooling — a two-minute rinse each month protects efficiency.
Shade and shut. Curtains closed on south-facing glass and doors shut to uncooled rooms cut the load the unit fights.
Use timers, not all-day running. Cooling the bedroom from 8pm beats running it from noon. Inverter units pull a room down fast.
A typical 2.5kW single-room split system might draw roughly 0.7–0.8kWh during steady cooling, which at the July–September 2026 Ofgem average Direct Debit cap rate of 26.11p/kWh works out to about 18–21p per hour at that input. Bigger multi-room systems use more; modern inverter units draw less when holding temperature than when first cooling a hot room.
Running one room for eight hours on a hot day costs roughly £1.50–£1.80. A typical UK summer — call it 40 genuinely hot days — lands around £60–£75 per cooled room per year. Whole-house multi-splits running several rooms daily through a hot spell can reach £4–£6 per day.
Fixed split systems are two to three times more efficient than portable units. A portable unit venting through a window draws more power for less cooling because it fights its own exhaust heat. If a portable costs 45p per hour for mediocre cooling, a properly sized split delivers better comfort at around 20p.
Often, yes. Modern units are heat pumps capable of producing roughly 3–4kWh of heat per 1kWh of electricity in suitable conditions. At 26.11p/kWh electricity that is about 7–9p per delivered kWh before other losses. Actual seasonal performance and your tariff determine the comparison with gas; it is far more efficient than a resistive electric radiator.
Undersized units running flat out, oversized units short-cycling, dirty filters, poor room insulation and setting 18°C when 23°C is comfortable. Correct sizing from a proper survey matters more than the brand badge — an inverter unit sized right for the room sips power holding temperature.
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