Calculate energy use, running cost and CO₂ emissions for any air conditioner.
Capacity unit
Divide the cooling capacity (kW) by the COP to get the electrical power draw (kW). Multiply power draw by hours of use to get kWh. Then multiply by your electricity rate. For example: a 3.5 kW AC with COP 3.5 draws 1 kW, costs $0.16/hr at $0.16/kWh.
Modern central AC units require a minimum SEER of 14-15 in the US. A SEER of 18-25 is considered high efficiency. Mini-split units can reach SEER 30+. Higher SEER means lower running costs but a higher purchase price.
SEER (Seasonal Energy Efficiency Ratio) is measured in BTU/Wh and covers seasonal performance. COP (Coefficient of Performance) is a dimensionless ratio. To convert: COP ≈ SEER / 3.412. A SEER 16 unit has a COP of about 4.7.
Set the thermostat 2-3°F higher, use ceiling fans to spread cool air, seal air leaks, service the AC filter monthly, keep blinds closed during peak sun, and consider upgrading to a unit with SEER 20+ if your unit is over 10 years old.
This calculator uses the US average grid emissions factor of 0.4 kg CO₂ per kWh (EPA 2023). A typical 3.5 kW AC running 8 hours a day for 90 days emits around 400-600 kg CO₂/season, depending on SEER rating and local grid mix.
Air conditioners are typically one of the largest electricity consumers in a home — often accounting for 20-50% of summer electricity bills. The running cost depends on three factors: how much cooling you need (capacity), how efficiently the unit converts electricity into cooling (SEER/COP), and how long you run it.
A common misconception is that a larger AC automatically costs more to run. A 5 kW unit with COP 5 actually draws the same electrical power (1 kW) as a 3.5 kW unit with COP 3.5. What matters is the ratio: capacity ÷ COP = electrical power draw.
| AC Unit | Capacity | SEER | COP | Power draw | Cost/hr at $0.16 |
|---|---|---|---|---|---|
| Basic window unit | 6,000 BTU | 10 | 2.9 | 0.61 kW | $0.10 |
| Mid-range central AC | 24,000 BTU | 16 | 4.7 | 1.46 kW | $0.23 |
| Efficient mini-split | 18,000 BTU | 25 | 7.3 | 0.72 kW | $0.12 |
| High-end inverter unit | 24,000 BTU | 30 | 8.8 | 0.80 kW | $0.13 |
Costs at $0.16/kWh US average. Actual rates and performance vary.
This calculator estimates CO₂ using the US average grid emissions intensity of 0.4 kg CO₂ per kWh (US EPA eGRID 2023 national average: 0.386 kg/kWh). If you are on a renewable energy tariff your actual emissions may be significantly lower. European grids vary from about 0.05 kg/kWh (Norway, hydropower) to 0.60 kg/kWh (Poland, coal-heavy).