The Quick Answer
Central air conditioners cost $0.25–$0.75 per hour to run. Window units cost $0.06–$0.20 per hour. Mini-splits cost $0.08–$0.25 per hour. But these ranges depend heavily on unit size, efficiency rating (SEER), your electricity rate, and how hard the unit is working. Let's get specific.
AC Electricity Cost Formula
Cost per hour = (Watts ÷ 1,000) × rate per kWh
For a central AC rated in tons: 1 ton = approximately 1,200 watts (1.2 kW) for a modern high-efficiency unit, or up to 2,000 watts for an older low-efficiency unit.
Central Air Conditioner Costs
| AC Size | Typical Home Size | Efficiency | Watts | Cost/Hour (17¢) | Cost/Hour (33¢ CA) |
|---|---|---|---|---|---|
| 1.5 ton | 600–900 sq ft | 15 SEER | 1,200 W | $0.20 | $0.40 |
| 2 ton | 900–1,200 sq ft | 15 SEER | 1,600 W | $0.27 | $0.53 |
| 3 ton | 1,200–1,800 sq ft | 15 SEER | 2,400 W | $0.41 | $0.79 |
| 4 ton | 1,800–2,400 sq ft | 15 SEER | 3,200 W | $0.54 | $1.06 |
| 5 ton | 2,400–3,000 sq ft | 15 SEER | 4,000 W | $0.68 | $1.32 |
| 3 ton | 1,200–1,800 sq ft | 20 SEER | 1,800 W | $0.31 | $0.59 |
| 3 ton (old 10 SEER) | 1,200–1,800 sq ft | 10 SEER | 3,600 W | $0.61 | $1.19 |
Window Air Conditioner Costs
| Unit Size | Room Size | Watts | Cost/Hour (17¢) | Daily Cost (8 hrs) |
|---|---|---|---|---|
| 5,000 BTU | 100–150 sq ft | 450 W | $0.077 | $0.61 |
| 8,000 BTU | 200–350 sq ft | 720 W | $0.122 | $0.98 |
| 10,000 BTU | 300–450 sq ft | 900 W | $0.153 | $1.22 |
| 12,000 BTU | 400–550 sq ft | 1,080 W | $0.184 | $1.47 |
| 18,000 BTU | 700–1,000 sq ft | 1,620 W | $0.275 | $2.20 |
Mini-Split (Ductless) Air Conditioner Costs
Mini-splits are typically 20–30% more efficient than central AC systems and 40–60% more efficient than window units. A 12,000 BTU (1-ton) mini-split at 22 SEER draws about 545 watts — compared to a window unit of the same capacity at 1,080 watts.
| Mini-Split Size | SEER | Watts | Cost/Hour (17¢) |
|---|---|---|---|
| 9,000 BTU (0.75 ton) | 22 | 410 W | $0.070 |
| 12,000 BTU (1 ton) | 22 | 545 W | $0.093 |
| 18,000 BTU (1.5 ton) | 21 | 857 W | $0.146 |
| 24,000 BTU (2 ton) | 20 | 1,200 W | $0.204 |
Monthly Cooling Cost Estimates
If you run your AC 10 hours/day for 4 summer months (120 days):
- 3-ton central AC, 15 SEER, 17¢/kWh: $0.41 × 10 hrs × 120 days = $492/season
- 3-ton central AC, 20 SEER, 17¢/kWh: $0.31 × 10 hrs × 120 days = $372/season
- 3-ton central AC, 15 SEER, 33¢/kWh (CA): $0.79 × 10 hrs × 120 days = $948/season
- 12,000 BTU window unit, 17¢/kWh: $0.18 × 10 hrs × 120 days = $220/season
Factors That Change Your Actual Cost
- Thermostat setting: Each degree of setback saves 3–5%. Setting 78°F vs. 72°F saves 18–30% on cooling costs.
- Insulation and air sealing: A well-insulated home runs the AC less. The compressor cycles off when the set temperature is reached.
- AC maintenance: Dirty filters increase energy use 5–15%. Clean or replace filters monthly in heavy use periods.
- Refrigerant charge: Low refrigerant makes the system work harder. Have a technician check charge annually if you notice reduced cooling.
- Time of use: If you're on a TOU rate plan, running AC during peak hours (4–9 PM) can cost 2–3x more than off-peak hours.
Bottom Line
Central AC is the dominant electricity cost driver in warm-climate homes — a 3-ton unit running 10 hours/day can easily cost $400–$1,000 per cooling season depending on efficiency and electricity rates. The single best investment for high cooling costs is often a high-efficiency replacement when your old system fails, or improving insulation and air sealing to reduce how long the AC needs to run. Use our electricity cost calculator to model different efficiency scenarios for your specific rate and usage pattern.