September 7, 2026
How much electricity does central air conditioning use?
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A central air conditioner's compressor draws about 3,000-3,500 watts for a 2-ton system and 3,500-5,000 watts for a 3-ton system while it runs. It doesn't run continuously, though — on a mild summer day it might cycle for 6-10 hours of compressor time, and in a heat wave closer to 14-16 hours. That's roughly 20-40 kWh a day, so at the U.S. average rate of about 17 cents per kWh you're looking at $100-200 over a summer month, and more in hot, high-rate states. The calculator below lets you set the system size and the hours of compressor runtime for your own home and state.
Central air conditioning is usually the single biggest line on a summer electric bill. Unlike a window unit you can meter with a plug-in monitor, a central system is wired into the panel, so most people never see what it actually uses. Here's how to estimate it.
Watts by system size
Central AC is sized in tons, where one ton equals 12,000 BTU of cooling. The compressor and air handler together draw roughly:
- 2 ton (24,000 BTU): 2,800-3,500 watts
- 3 ton (36,000 BTU): 3,500-5,000 watts
- 4 ton (48,000 BTU): 4,700-6,000 watts
A higher SEER2 rating lowers those numbers for the same cooling output, and a two-stage or variable-speed compressor spends much of its time at a fraction of full draw rather than switching fully on and off.
It doesn't run all the time
The key to estimating cost is compressor runtime, not clock hours. On a mild day a properly sized system might run 30-50% of the time — call it 8-12 hours of actual compressor time across 24 hours. In a heat wave, or with an undersized system or a poorly sealed house, it can run 70-90% of the time.
For a 3-ton system at 4,000 watts:
- Mild summer day, 9 hours runtime: 36 kWh -> about $6 at 17 cents/kWh
- Heat wave, 18 hours runtime: 72 kWh -> about $12 a day
- A hot month averaging 40 kWh/day: about $200
What moves the number
Thermostat setting is the biggest lever: every degree lower roughly adds 6-8% to runtime. After that come insulation and air sealing, duct leakage (often 20-30% of conditioned air lost in older homes), a dirty filter or coil, and your climate zone. Your electricity rate then scales all of it — the same 40 kWh/day costs about $130 a month in a low-rate state and $350 in California.
Estimate it for your home
The calculator below is set to a 2-ton system on a U.S. state rate. Bump the size to match your unit, set the hours to your best guess at daily compressor runtime, and switch to your own state. To see how central air compares with cooling individual rooms, run a window unit through the main AC calculator on the same rate.