A method you can check
An air conditioner can be switched on for a long period without drawing its rated electrical input continuously. The compressor may cycle, or an inverter-driven system may vary speed to match the cooling load. The result depends on both the equipment and the room conditions.
Four inputs that matter
- Electrical input: use the watts or kW drawn from the electrical supply, not the cooling capacity.
- Available hours: how long the unit is on or expected to maintain the set temperature.
- Average load: a planning fraction that represents the share of rated input used on average.
- Electricity tariff: your charge per kWh, noting that some tariffs change by time or usage band.
Why the average load changes
Hotter outdoor temperatures, direct sunlight, air leaks, high humidity, an undersized unit, and a low thermostat setting can increase demand. Shading, suitable insulation, clean filters, closed doors, and correct equipment sizing can change the load. These factors are not captured by a fixed watt rating alone.
Use scenarios, not false precision
If you do not have measured data, calculate more than one scenario. A lower running fraction represents shorter or lighter compressor operation; a higher fraction represents more sustained operation. Keep all other inputs unchanged to see how sensitive the cost is to this assumption. Do not present a guessed running fraction as a measured efficiency.
Ways to compare operating patterns
Compare a typical day with a very hot day, or compare two schedules. Record the outdoor conditions and indoor setpoint if you want the comparison to remain interpretable. For a real assessment of equipment performance or sizing, use manufacturer data and a qualified HVAC professional.
The Air Conditioner Cost Estimator makes the running-fraction assumption explicit so it can be changed and discussed.
Related resources
Continue with the Electricity Cost Calculator, the Home Energy Planner, or the Appliance Comparison Calculator depending on the question you are trying to answer.
References and further reading
The U.S. Federal Trade Commission offers a consumer guide to heating and cooling costs, including what to consider when comparing equipment. The U.S. Department of Energy's home energy checklist includes basic maintenance steps such as following the manufacturer's filter instructions.
These guides do not predict the consumption of your specific unit. Use measured input energy or manufacturer data when available, and ask a qualified HVAC professional about equipment sizing or repair.