The electrical input of a system changes as conditions change. A correctly sized inverter system normally adjusts its output after the room approaches the selected temperature. Actual cost therefore depends on the equipment, weather, building and way the system is used.
Worked running cost example
For an illustration, assume average electrical input of 0.8 kW, 6 hours of use each day for 30 days and an electricity tariff of 25p per kWh. The calculation is 0.8 x 6 x 30 x £0.25 = £36 for that month. If average input is 0.4 kW under the same assumptions, the result is £18. The tariff and electrical inputs here are examples, not promises of actual use or a quoted tariff.
Use the selected model electrical input and your current supplier tariff for a personal estimate. Cooling capacity, such as 2.5 kW, is not the same as electrical input. Inverter input changes with demand, and this example excludes any standing charge. Example prepared 8 October 2026.
Capacity and sizing
An undersized unit may run hard without achieving the required comfort. An oversized unit can cycle inefficiently and control temperature poorly. Proper sizing considers the room heat load rather than selecting equipment from floor area alone.
Efficiency ratings
SEER describes seasonal cooling efficiency and SCOP describes seasonal heating efficiency. Higher figures indicate that more useful cooling or heating is delivered for each unit of electricity under the rating conditions. Compare like for like models and capacities.
Room and building factors
Large windows, direct sun, weak insulation, open doors, high ceilings and internal equipment increase the load. Blinds, shading, sensible ventilation and reduced unwanted heat gain can lower the work required from the system.
Temperature settings
Very low cooling settings increase demand and may not improve comfort proportionally. A stable, sensible setting with doors and windows managed appropriately is usually more efficient than repeatedly switching between extremes.
Calculating an estimate
Find the unit electrical input in kilowatts, multiply it by the expected operating hours, then multiply by the electricity tariff. This gives a simple upper planning figure. Inverter operation means real consumption can be lower once the room reaches temperature.
Heating with a split system
Many split systems are reversible heat pumps. Their heating running cost depends on outdoor temperature, system efficiency, required room temperature and the performance of the building. Compare the expected use and current heating method rather than relying on one headline figure.
Electricity tariffs and operating conditions vary. Use current supplier prices and the selected model data when producing a personal estimate.