Efficiency Comparison Calculator

Your room

Enter input power in kW for the most accurate result (from the spec sheet or energy label). Alternatively, enter cooling capacity in BTU and the unit's EER rating. Use SEER only where seasonal performance figures are appropriate (inverter units).

Unit A

Input power (kW) optional

Cooling capacity (BTU) optional

EER rating optional

Purchase price (£) optional

Used to calculate payback period if units differ in price.

Unit B

Input power (kW) optional

Cooling capacity (BTU) optional

EER rating optional

Purchase price (£) optional

Used to calculate payback period if units differ in price.

Hours used per year

Typical UK usage: 300–500 hours per year.

Electricity rate (p/kWh)

Pre-filled with the current Ofgem price-cap rate. Adjust if you're on a different tariff.

Result

Enter power details for both units to compare running costs.

How we calculated this

Annual cost formula: Input power (kW) × hours per year × rate (£/kWh)

When input power is not available, it is estimated from cooling capacity and EER: Input power = Cooling capacity (W) ÷ EER.

If purchase prices are provided, the payback period is: Price difference ÷ Annual savings. If the more efficient unit is also cheaper upfront, no payback is needed.

Based on the Ofgem cap for 2026-04-01–2026-06-30, last checked 2026-05-29. Source: https://www.ofgem.gov.uk/energy-price-cap

Higher EER or lower input power means lower running costs — but a more efficient unit often costs more upfront. This calculator shows the annual saving and how long it takes for a more efficient unit to pay back its extra cost.

Not sure what size unit you need? Use the BTU calculator. Want to estimate costs for a single unit? Use the running cost calculator.