Air Conditioning Running Cost Calculator

This calculator works out what a central air conditioner, heat pump or mini-split costs to run for cooling, per day and per year. It takes the numbers printed on the unit's EnergyGuide label and the rate from your electric bill, runs in your browser, and shows the formula so you can check each step.

How the air conditioning running cost calculator works

SEER2 is a ratio of cooling delivered to electricity used, in BTU per watt-hour. Divide the unit's capacity in BTU/h by SEER2 and you have its average electrical draw in watts; divide by 1,000 for kilowatts. Multiply by the running hours to get the kWh used in a day, by your price per kWh for the daily cost, and by the cooling days for the year.

The default is a 2-ton system (24,000 BTU/h) rated 15 SEER2. It draws 24,000 ÷ 15 = 1,600 W, or 1.6 kW. Eight running hours use 12.8 kWh, which is $2.30 a day at $0.18/kWh. Over 120 cooling days that is 1,536 kWh and $276.48 for the season.

Efficiency moves the number in direct proportion. A 3-ton system (36,000 BTU/h) on the same 8 hours, 120 days and $0.18 costs $388.80 a season at 16 SEER2 and $464.24 at 13.4 SEER2, a difference of about $75 every year. For readers elsewhere: SEER2 × 0.293 gives the equivalent seasonal COP, so 15 SEER2 is a COP of about 4.4, and 12,000 BTU/h (one ton) is about 3.5 kW.

What you enter

Five numbers. Cooling capacity and SEER2 come off the yellow EnergyGuide label or the unit's AHRI certificate; if the label is gone, the model number looks both up in the AHRI Certification Directory. Units rated before 2023 show plain SEER, which comes out about 4.5% lower when retested as SEER2, so a 14 SEER unit is roughly 13.4 SEER2. Window and portable units are rated in CEER instead, which is also BTU per watt-hour and can go in the SEER2 field for a rough figure. The electricity price should be your all-in rate: total bill divided by kWh used, which folds in delivery charges and taxes. If you have no bill to hand, EIA publishes the average residential price for each state, updated monthly.

Running hours are the hardest input to pin down. They mean hours the compressor actually runs, not hours the thermostat is set to cool, and a correctly sized system in mild weather cycles off for much of the day. A smart thermostat's runtime report gives the real figure; without one, the default 8 hours suits a hot summer day in much of the South, and fewer hours suit milder climates.

Reading the result

The annual figure is what cooling adds to your electric bill, and the annual kWh row lets you compare it with your bills directly: the rise in kWh between spring and a summer month is roughly what the AC used that month. SEER2 is a seasonal average, so the estimate is best for a whole summer and weakest for a single heat wave, when efficiency drops. EER2, also on the label, is the efficiency at a 95°F outdoor temperature, and in very hot climates it is the better guide to peak-day cost.

If you pay time-of-use rates, the average price understates cooling cost, because air conditioning runs hardest in the late-afternoon peak. Enter the peak rate, or a weighted mix, for a truer figure.

Safe by design

This is an operating-cost estimate only. Installing or repairing the system is regulated work: anyone handling refrigerant must hold EPA Section 608 certification, and the electrical supply is a job for a licensed electrician working to the National Electrical Code as adopted in your area. A new system also usually needs a mechanical permit from the local building department.

Assumptions and limits

The model assumes the unit draws its rated average power for every running hour. Real use varies with outdoor temperature, humidity, thermostat setting, duct losses and how well the house is sealed and insulated. Variable-speed and inverter units spend much of their time at part load, which is where their SEER2 advantage comes from, so for them the running hours are better thought of as full-output equivalent hours. The blower on a central system is included in the SEER2 rating, but a dehumidifier or a second air handler is not.

Prices, hours and days are all your own inputs, so nothing here goes out of date. A heat pump's heating season is a separate calculation, rated in HSPF2 rather than SEER2.

Using it with the rest of BuildMetricLab

Running cost sits at the end of the sizing work. The AC sizing calculator estimates the BTU/h a room needs, the multi-room sizing calculator adds up the load across up to four rooms and suggests whether one split system or a multi-split suits, and the AC ducting length calculator measures the supply run for a ducted system. Every BuildMetricLab tool runs in your browser, with no sign-up and nothing sent to a server, and shows its formula so the math can be audited.