Appliance cost · 7 min read
How much does it cost to run an air conditioner per hour?
A typical central AC costs about 58¢ an hour to run at US-average rates. A window unit runs 8-25¢. The nameplate watts tell you the ceiling; duty cycle tells you the actual number.
The short answer by AC type
At the US-average rate of 16.5¢/kWh, here's what an hour of runtime costs for each common AC setup, assuming the compressor is actively pulling its typical wattage:
- Window AC (5,000-8,000 BTU): 500-900W, about 8-15¢/hour
- Window AC (10,000-15,000 BTU): 1,000-1,500W, about 17-25¢/hour
- Portable AC: 800-1,500W, about 13-25¢/hour
- Mini-split (single-zone): 600-1,200W, about 10-20¢/hour
- Central AC (2.5-3 ton): 3,000-3,500W, about 50-58¢/hour
- Central AC (4-5 ton): 4,500-5,500W, about 74-91¢/hour
Why nameplate watts overstate the real cost
An AC doesn't run flat-out for every hour it's "on." The compressor cycles: it pulls full wattage until the room hits setpoint, shuts down, and kicks back on when the temperature drifts. That cycling is called duty cycle, and it's the difference between a quoted hourly cost and what shows up on your bill.
A central AC in a reasonably tight house on an 85°F day runs at roughly a 40-50% duty cycle. On a 95°F day in a leakier house it can push 70-80%. So the 58¢/hour figure above is what it costs while the compressor is running. Multiply by the duty cycle to get the cost per wall-clock hour: a 3,500W central AC at 16.5¢/kWh with a 50% duty cycle actually costs about 29¢ per hour the system is turned on.
Key insight
The duty cycle is why two identical ACs cost different amounts.
The math, once
Every AC follows the same formula. Watts, times hours, times the per-kWh rate, divided by a thousand, times the duty cycle:
hourly cost = (watts × rate in $/kWh × duty cycle) ÷ 1000
A 1,200W window unit at 16.5¢/kWh running at 60% duty cycle: (1200 × 0.165 × 0.60) ÷ 1000 = $0.119/hour, or about 12¢. Run it 10 hours on a hot afternoon: $1.19 in electricity.
Run your setup through the calculator
Plug in your unit's wattage (check the nameplate on the side or back of the unit), your typical daily runtime, and your local rate:
Estimated cost
A central air conditioner draws full power only while the thermostat/compressor is running — about 9.8 effective hours at 3500W across your 14-hour window.
For a detailed breakdown by AC type with efficiency tips, see the central AC and window AC pages.
The same AC in different states
Regional rates swing this number as much as AC type does. A 3,500W central unit running 8 hours at 50% duty cycle on a summer day:
- In Idaho at 11.1¢/kWh: $1.55 a day
- In Texas at 14.8¢/kWh: $2.07 a day
- US average at 16.5¢/kWh: $2.31 a day
- In California at 31¢/kWh: $4.34 a day
Over a 90-day cooling season that's a $251 spread between Idaho and California for the identical piece of equipment doing identical work.
Levers that actually move the number
Thermostat setpoint. Every 1°F you raise the summer setpoint is worth 6-8% on cooling cost. Going from 72°F to 76°F saves roughly 25-30% on AC runtime. The compressor cycles less because the system has less work to do.
SEER rating.A 20 SEER central AC uses about 30% less power than a 14 SEER one for the same cooling output. On a $1,000 summer cooling bill, the efficiency delta is worth roughly $300 a year. The payback on a full replacement is typically 8-15 years; the payback is shorter if you're replacing a failed unit anyway.
Envelope. Sealed ducts, weather-stripped doors, and attic insulation drop the duty cycle, not the wattage. A typical older house loses 20-30% of its cooled air through duct leaks alone. Duct sealing runs $300-600 and cuts cooling cost 10-15% on average.
Common scenarios priced out
A few worked examples to anchor the numbers:
- A 6,000 BTU window unit in a bedroom, running 8 hours overnight at 65% duty cycle on 600W, at 16.5¢/kWh: 20¢ a night, about $6 a month in peak summer.
- A 12,000 BTU portable AC in a home office, running 9 hours a weekday at 70% duty cycle on 1,200W, at 16.5¢/kWh: $1.25 a day, about $27 a month.
- A 3-ton central AC in a 2,000 sq ft house, running 10 hours a summer day at 55% duty cycle on 3,500W, at 16.5¢/kWh: $3.17 a day, about $95 a month across a three-month cooling season.
- A mini-split in a single room, running 12 hours a day at 40% duty cycle on 900W, at 16.5¢/kWh: 71¢ a day, about $22 a month.
These are steady-state numbers. Actual monthly bills vary by weather, envelope tightness, and how aggressive the setpoint is versus the outdoor high. A few consecutive 100°F days can push any of these numbers up 40-60%.
The quick rule of thumb
For a back-of-envelope estimate, take your AC's nameplate watts, multiply by your rate per kWh in dollars, divide by 2,000. That gives you a realistic cost-per-hour-on for a typical central or window unit at moderate duty cycle. Refine with the calculator above when you need the number to the cent.