Quick answer: A 3-ton central air conditioner draws roughly 3,300 watts while running. At the US average rate of 18.2¢ per kWh that is about $0.60 per hour of compressor run time, or about $144.14 a month if it runs 8 hours a day.
Central air is usually the biggest single electricity cost in a US home in summer. The bill depends on the size and efficiency of the system and, above all, how many hours the compressor runs.
Central AC running costs by system size
| System size | Power | Hours a day | US per hour | US per day | US per month |
|---|---|---|---|---|---|
| 2-ton (24,000 BTU) | 2,200 W | 8 | $0.40 | $3.20 | $96.10 |
| 3-ton (36,000 BTU) | 3,300 W | 8 | $0.60 | $4.80 | $144.14 |
| 4-ton (48,000 BTU) | 4,400 W | 8 | $0.80 | $6.41 | $192.19 |
| 5-ton (60,000 BTU) | 5,500 W | 8 | $1.00 | $8.01 | $240.24 |
On a very hot spell the compressor may run 12 hours or more a day: for a 3-ton system that is about $216.22 a month.
Run time is what you pay for
The compressor switches on and off to hold your thermostat setting. Hotter weather, a lower setting, poor insulation, sun on the windows and leaky ducts all keep it running longer. ENERGY STAR estimates that a typical duct system loses 20 to 30% of the air that moves through it through leaks and poor connections.
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How to lower your cooling bill
- Raise the thermostat. 78°F when you are home is the US Department of Energy’s suggested setting. Turning it up 7 to 10°F for 8 hours a day while you are out can save up to 10% a year on heating and cooling.
- Use ceiling fans so a higher setting feels cooler. Turn them off when you leave the room.
- Change the filter regularly; a clogged filter makes the system work harder.
- Seal and insulate ducts in attics, garages and crawl spaces.
- Shade sunny windows and avoid using the oven and dryer in the hottest part of the day.
- Have the system serviced and the outdoor coil cleaned before summer.
Frequently asked questions
Is it cheaper to leave the AC on all day?
Generally no. Raising the setting while you are out reduces the hours the compressor runs. Very humid climates and some heat pump systems benefit from moderate rather than large setbacks.
How do I know how big my system is?
The model number on the outdoor unit usually includes the capacity in thousands of BTU: 24 is 2 tons, 36 is 3 tons, 48 is 4 tons.
Why did my summer bill jump?
Longer run times in a heat wave, rate increases and leaky ducts are the usual causes. See why your electric bill is so high.
A real example: a hot July
A 3-ton system that runs about 10 hours a day during a heatwave uses roughly 1,023 kWh a month: about $186.19 at the US average rate. In a milder month with 5 hours of run time a day, the same system uses about 512 kWh, roughly $93.09.
Your own rate matters a lot: in a state charging 30¢ per kWh, the heatwave month would cost about $306.90.
Maintenance that keeps cooling costs down
- Replace or clean the air filter every 1 to 3 months during the cooling season.
- Keep the outdoor unit clear of leaves, grass and plants, with about 2 feet of space around it.
- Have the system serviced every year or two, especially if it struggles to cool or ices up.
- Seal and insulate ducts in hot attics, where leaks can waste a large share of cooled air.
- Use ceiling fans so you can set the thermostat a few degrees higher and feel just as cool.
More questions readers ask
What does SEER2 mean?
SEER2 is the efficiency rating for central air conditioners. A higher number means more cooling per kWh. New systems in most of the US must meet a minimum of about 13.4 to 14.3 SEER2 depending on region.
Is a heat pump cheaper to run than central AC?
For cooling they work the same way and cost about the same. The difference is that a heat pump can also heat the home efficiently in winter.
Sources
- U.S. Department of Energy, Programmable thermostats.
- ENERGY STAR guidance on duct sealing.
- U.S. Energy Information Administration, Short-Term Energy Outlook.
- Our methodology.