Calculate an AC-only electricity-use scenario
Air-conditioner size is often described in tons of cooling capacity, with one ton equal to 12,000 Btu per hour of cooling output. That capacity does not mean the unit draws a fixed number of kilowatts throughout the day. To estimate annual electricity from an efficiency rating, start with the cooling delivered during an assumed season: nominal capacity multiplied by equivalent full-load cooling hours. Then divide seasonal delivered Btu by the system's SEER2 value, measured in Btu per watt-hour, and convert watt-hours to kilowatt-hours.
Equivalent full-load hours combine varying load conditions into the number of hours that would provide the same amount of cooling if the unit operated at nominal output. They are not the number of clock hours with a running fan or thermostat. Use a location-appropriate analysis or utility study for this assumption. The tool isolates cooling-system energy and uses an editable energy price; it does not imply that the resulting charge is the entire electricity bill.
Cooling capacity, SEER2 and electricity formulas
Seasonal cooling output (Btu) = nominal output × equivalent full-load hours
Annual cooling electricity (kWh) = seasonal cooling output ÷ SEER2 ÷ 1,000
Annual modeled electricity charge = kWh × electricity rate
Example: a three-ton AC system
A three-ton air conditioner has a nominal cooling output of 36,000 Btu per hour. At 900 equivalent full-load hours, the annual modeled cooling is 32.4 million Btu. With a SEER2 of 15, that represents 2,160 kWh of electricity under this simplified scenario. At $0.18 per kWh, the corresponding modeled cooling energy charge is $388.80.
Changing annual equivalent full-load hours from 900 to 1,200 raises the result by one-third, even though capacity and rating remain unchanged. That illustrates why the local climate, cooling demand and occupancy schedule can matter more than small differences in equipment labels.
What the SEER2 calculation does not measure
SEER2 is a standardized seasonal efficiency rating. It is not a precise measurement of power draw at every outdoor temperature, and the system's delivered cooling may be lower than its nominal nameplate capacity at certain conditions. Duct leakage, refrigerant charge, airflow, controls, thermostat settings and maintenance all affect what occupants receive. Heating electricity, portable appliances, fan-only operation and utility fixed charges are outside this calculator's AC-only scenario.
If actual monthly usage data is available, compare cooling-season consumption with shoulder-season months only after accounting for other electric loads. That can produce a more defensible reference than a guessed full-load-hours input. Use the same cooling demand when comparing SEER2 ratings; otherwise a claimed equipment saving may simply reflect different weather or household behavior.
Air conditioner electricity questions
Is one ton of cooling the same as one kilowatt of electricity?
No. One cooling ton is a rate of thermal cooling equivalent to 12,000 Btu per hour. Electrical input depends on equipment efficiency and operating conditions, so capacity alone does not establish the electric power consumed.
Can I enter total compressor-running hours?
Only if you can translate the load variation into equivalent full-load hours. A variable-speed system can run at reduced output for extended periods, so clock hours may overstate the cooling delivered when treated as full-output hours.
Why does the result change so much with SEER2?
For the same seasonal cooling output, electricity is inversely proportional to SEER2 in this simplified model. Higher ratings reduce the modeled kWh requirement, but real savings still depend on the actual system and building operating conditions.