How Much Does It Cost to Run an Air Conditioner?
Central AC costs about 42¢ an hour to run at the US average rate; a window unit about 12¢. Compare all three types and get the cost in your state.
At the US average rate of 18.44¢/kWh, a 3-ton central air conditioner costs about 42¢ per hour of compressor runtime, a window unit about 12¢, and a portable unit about 17¢. Over a 120-day cooling season at eight hours a day, that is roughly $402, $112 and $159 respectively.
Air conditioners are cycling appliances, so hours of runtime matter more than hours the thermostat is switched on. A correctly sized system runs 60–70% of the time on a hot day; an oversized one short-cycles, cools less comfortably, and costs more. The calculator accounts for this.
- Per month
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- Per day used
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- kWh / year
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Central vs window vs portable
| Appliance | Watts | Duty | kWh/yr | Cost/yr |
|---|---|---|---|---|
| Central air conditioner | 3,500 W | 65% | 2,184 | $403 |
| Ductless mini-split | 1,200 W | 60% | 1,080 | $199 |
| Portable air conditioner | 1,200 W | 75% | 864 | $159 |
| Window air conditioner | 900 W | 70% | 605 | $112 |
| Ceiling fan | 60 W | 100% | 86 | $15.9 |
Per hour, a window unit looks like a bargain against central air. Per square foot cooled the gap closes sharply — one window unit cools one room, and three window units running simultaneously cost more than a properly sized central system doing the same job.
Single-hose portable air conditioners exhaust hot air out of a window, which lowers the pressure in the room. That pulls unconditioned outside air in through every gap in the building. You are cooling air, then paying to replace it with hot air. Real-world efficiency is often 30–40% worse than the rating implies, which is why the table shows portables costing more than window units despite similar wattage. Dual-hose models avoid most of this.
Central AC cost by hours of runtime
| Usage | kWh/day | Per day | Per 30 days | Per season |
|---|---|---|---|---|
| 2 hr/day | 4.55 | 84¢ | $25.17 | $101 |
| 4 hr/day | 9.10 | $1.68 | $50.34 | $201 |
| 6 hr/day | 13.65 | $2.52 | $75.51 | $302 |
| 8 hr/day | 18.20 | $3.36 | $101 | $403 |
| 12 hr/day | 27.30 | $5.03 | $151 | $604 |
| 16 hr/day | 36.40 | $6.71 | $201 | $805 |
A 3-ton, 14 SEER2 system drawing about 3,500 W including the air handler is the baseline here. A 20 SEER2 inverter system doing the same cooling work draws closer to 2,400 W — roughly a 30% cut on every line of that table.
What SEER2 actually saves you
SEER2 is cooling output divided by electricity input across a simulated season. Higher is better, and the relationship is straightforwardly proportional: going from 14 SEER2 to 18 SEER2 cuts consumption by about 22%, because 14 ÷ 18 = 0.78.
That is a real saving, but it takes a long time to repay a several-thousand-dollar equipment premium on its own. High-SEER2 equipment makes financial sense when you are replacing a failed system anyway, when your rate is well above average, or when your cooling season is long. In Arizona or Florida the same upgrade pays back two to three times faster than in Michigan.
Cooling season cost by state
| State | Rate | Cost | vs US avg | |
|---|---|---|---|---|
| Idaho | 12.35¢ | $270 | −133 | below average |
| Texas | 16.44¢ | $359 | −43.7 | below average |
| Florida | 15.17¢ | $331 | −71.4 | below average |
| Ohio | 19.52¢ | $426 | +23.6 | near average |
| Pennsylvania | 21.55¢ | $471 | +67.9 | above average |
| New York | 29.93¢ | $654 | +251 | above average |
| California | 33.25¢ | $726 | +323 | above average |
| Hawaii | 52.00¢ | $1,136 | +733 | above average |
The thermostat maths
Each degree you raise the cooling setpoint saves roughly 3% of cooling energy. The saving is not linear with comfort, though — the first two degrees are nearly free comfort-wise, and the fifth is where most people give up.
- 78°F instead of 72°F cuts cooling cost by roughly 18%. On a $400 season that is $72.
- Ceiling fans let you go 4°F higher at the same perceived comfort, and a fan costs about a fiftieth of what the AC costs per hour. Turn them off when you leave the room — they cool people, not air.
- Setbacks work, but not aggressively. Letting the house climb to 85°F while you are out saves real money; letting it hit 95°F means the system runs flat out for hours to recover, and in humid climates it never catches up on moisture.
A clogged filter can cut airflow enough to raise consumption 5–15%, and a dirty outdoor condenser coil does the same again. Both are free to fix. Do these before spending anything on efficiency upgrades.
Frequently asked questions
How much does it cost to run a window AC for 8 hours?
About 93¢ at the US average of 18.44¢/kWh, assuming a 900 W unit at a 70% duty cycle. A small 5,000 BTU unit costs roughly half that; a 12,000 BTU unit roughly 40% more.
Is it cheaper to leave the AC on all day or turn it off?
Turning it off — or setting it back — is cheaper. A house loses heat to the outside faster the colder it is inside, so letting the temperature drift up while you are out reduces total heat gain. The recovery run does not cancel the saving. The exception is very humid climates, where a deep setback lets moisture build up that is expensive to remove again.
Does AC use more electricity than a heater?
Usually less, per hour. A 3-ton central AC draws about 3,500 W; an electric furnace draws 15,000 W. Air conditioners move heat rather than creating it, which is inherently cheaper than resistance heating. Over a year the comparison depends entirely on your climate.
What size air conditioner do I need?
Roughly 20 BTU per square foot as a starting point — 12,000 BTU (1 ton) for 600 sq ft. Oversizing is a real problem with air conditioning: an oversized unit cools fast, shuts off before it removes humidity, and leaves the house cold and clammy while cycling inefficiently.
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