How it is calculated
Capacity is first converted to watts (1 BTU/h = 0.293 W; 1 frigoría/h = 1.163 W). Electrical power is capacity ÷ EER: a 12,000 BTU/h (3.5 kW) unit with an EER of 3.5 draws about 1,000 W when the compressor runs flat out.
Because the compressor is not always at full load, a load factor is applied. Energy (kWh) = power (W) × factor × hours ÷ 1,000. Cost is energy times your price per kWh.
Worked example
Using the calculator’s example values:
- What do you know about the unit?: Cooling capacity in kW
- Cooling capacity: 3.5 kW
- Efficiency EER / SEER: 3.2
- Hours of use per day: 6 h/day
- Days of use per month: 30 days/month
- Average load factor: 70%
- Months of use per year: 3 months/year
- Electricity price: $0.15/kWh
Result: Estimated monthly cost — $20.67 (monthly consumption: 137.81 kWh; cost per day of use: $0.69; cost per hour: $0.11).
Money-saving tips
- Every degree higher on the thermostat reduces compressor work; try 77–79 °F (25–26 °C) in summer.
- Clean the filters: a clogged filter makes the unit work harder for the same comfort.
- Close blinds and awnings during sunny hours to cut the heat load.
Frequently asked questions
How many BTU do I need per square foot?
It depends on insulation, orientation and ceiling height, so any fixed figure is only a rough guide. For reliable sizing ask an installer for a heat-load calculation.
What is the difference between EER and SEER?
EER measures efficiency at one specific test condition; SEER is seasonal and better reflects real use over a summer. If you have SEER use it, and be cautious about lowering the load factor further.
Does an inverter unit use more?
No: an inverter adjusts compressor speed and avoids constant stop-start cycles, so its average load factor is usually lower than a fixed-speed unit’s.
How we calculate and the limits of the results: Methodology.