Window AC vs Central AC Cost Calculator
Compare what room air conditioners and a central system cost to run, and see how long a higher price takes to pay back.
Sample numbers only, to show how it works. Replace them with yours.
Enter how many days a year you run the air conditioning.
This is an estimate, not a professional calculation. See the disclaimer and the methodology.
How it is calculated
For each system the calculator works out the electric power it draws while it runs: capacity in Btu per hour, divided by the efficiency rating, divided by 1,000, gives kilowatts. With several identical units, multiply by the number of units.
Energy = power × hours a day × days of cooling. Cost = energy × price per kWh. The cost per 30 days of use is the daily cost times 30. Nothing is added for fixed charges, taxes or demand charges.
The efficiency rating is the one printed on the unit: CEER or EER for a window or wall unit, SEER2 for a central system. In short, each says how much cooling in Btu you get for each watt-hour of electricity (our summary of the metrics: check the definition for your own label). A higher rating means less electricity for the same cooling. The calculator uses the number you enter as a constant.
The hours a day are hours at full capacity. A unit that cools a room and then cycles off counts only the time it runs. Whole-house systems tend to run more hours than a unit in one room, because they cool more space, so each system has its own hours field.
The price starts at the 2024 average residential price EIA reports for your state, an annual average. If your summer rate is different, replace it with the rate on your bill.
If you enter the installed price of both systems, the calculator divides the extra price of the dearer one by its yearly running saving. That is a simple payback. It ignores repairs, equipment life, interest and the value of comfort, and it is blank when the dearer system does not cost less to run.
Comparing the two only makes sense if both cool the space you care about. Use the AC BTU calculator to size room units. Central systems are sized by a contractor.
Worked examples
Three window units against a central system
Three 8,000 Btu/h window units at a rating of 11, running 6 hours a day, against one 36,000 Btu/h central system at a rating of 16 running 8 hours a day (all assumed for this example). Over 120 days at the U.S. average of 16.5 cents per kWh (2024), the window units cost $259 and the central system costs $356.
Same hours, different result
Run the central system only 6 hours a day, as the window units do, and its season cost falls to $267 against $259 for the window units. Hours often move the answer more than the rating, so enter the hours you really expect.
Is the dearer system worth it?
Say the window units cost $1,800 installed and a central system with a rating of 20 costs $7,500 (assumed prices). The central system saves -$26 a year in electricity, so the extra $5,700 takes about longer than any equipment lasts to be paid back by running costs alone.
Frequently asked questions
Is a window air conditioner cheaper to run than central air?
It depends on how much space each cools, how many hours each runs and their efficiency ratings. A single room unit uses less power than a whole-house system, but a house may need several. The calculator compares them for your numbers.
What are CEER, EER and SEER2?
They are efficiency ratings printed on air conditioners. CEER and EER are used for window and wall units, and SEER2 is used for central systems. A higher number means less electricity for the same cooling. They are measured by different test procedures, so compare a window unit with a central system as a rough guide.
Where do I find the rating and the capacity?
On the label of the unit, in the product listing, or on the EnergyGuide sticker. Capacity is in Btu per hour. A ton is 12,000 Btu per hour.
How many hours a day should I enter?
Enter the hours the unit would take at full capacity. A reasonable start is the hours the air conditioner is on, then lower it if the unit often cycles off. If you have a past summer of bills, adjust the hours until the result matches the cooling part of the bills.
Does the payback include repairs or the life of the equipment?
No. It divides the extra price by the yearly saving in electricity. Equipment of different ages, repairs and rebates are not included.
Why is the price an annual average?
The 2024 state averages are the latest full-year figures we have checked. Your summer rate may be higher or lower, or may change with time of day. Use the rate on your bill when you can.
Related calculators
Sources and last update
- U.S. Energy Information Administration, 2024 Average Monthly Bill, Residential (average price by state)
- ENERGY STAR, Room Air Conditioners key product criteria (CEER)
- U.S. Department of Energy, Consumer central air conditioners and heat pumps (SEER2 standards)
- U.S. Energy Information Administration, copyrights and reuse
Last updated: November 3, 2026. See methodology and sources.