How Much Does It Cost to Run Central AC?
A typical 3-ton central air conditioner draws about 3,500 watts while the compressor is running. At the 2024 US average rate of $0.16/kWh, that is $0.56 per hour, $4.48 for an 8-hour day, and $134.40 a month if the compressor cycles 8 hours every day. Over a full 150-day cooling season, the same usage adds up to about $672. Real bills usually land lower because the compressor cycles off once the thermostat hits setpoint.
Want the cost for a different tonnage, SEER rating, or your exact utility rate? Use the appliance cost calculator or compare central air to a single-room option on the window AC cost page.
The Formula
Cost = (watts ÷ 1,000) × hours per day × days × price per kWh
Dividing watts by 1,000 converts to kilowatts (kW). Multiplying by hours gives kilowatt-hours (kWh) — the unit your utility bills you in. Multiply by your price per kWh and you have the cost. For central AC, “hours” should be hours of actual compressor runtime per day, not just hours the thermostat is set to cool.
Worked example (3-ton / 3,500W central AC, 8 h/day, 30 days, $0.16/kWh): (3,500 ÷ 1,000) × 8 × 30 × 0.16 = 3.5 kW × 240 hours × $0.16 = $134.40 per month.
Cost by Compressor Runtime
For a 3-ton / 3,500W central AC at $0.16/kWh (the US average). “Hours” is hours of compressor runtime — the thermostat may be set to cool all day, but the compressor only runs part of that time. Seasonal cost assumes a 150-day (May-September) cooling season at the row's daily runtime.
| Hours per day | kWh per day | Cost per day | Cost per month | Cost per season |
|---|---|---|---|---|
| 4h | 14.0 | $2.24 | $67.20 | $336 |
| 6h | 21.0 | $3.36 | $100.80 | $504 |
| 8h (baseline) | 28.0 | $4.48 | $134.40 | $672 |
| 12h | 42.0 | $6.72 | $201.60 | $1008 |
Cost by Central AC Size (Tonnage)
Central AC capacity is measured in tons — one ton equals 12,000 BTU/hour of cooling. Wattage scales roughly with tonnage at a given SEER. This table assumes 8 hours of compressor runtime per day at $0.16/kWh and a SEER ~10 baseline system. Seasonal cost covers a 150-day cooling season.
| Unit size | Watts | Cost per hour | Cost per month | Cost per season |
|---|---|---|---|---|
| 2 ton (~1,000-1,300 sq ft) | 2,300 | $0.37 | $88.32 | $442 |
| 2.5 ton (~1,300-1,600 sq ft) | 2,900 | $0.46 | $111.36 | $557 |
| 3 ton (~1,600-2,000 sq ft) (baseline) | 3,500 | $0.56 | $134.40 | $672 |
| 4 ton (~2,000-2,500 sq ft) | 4,700 | $0.75 | $180.48 | $902 |
| 5 ton (~2,500-3,000 sq ft) | 5,800 | $0.93 | $222.72 | $1114 |
Cost by SEER Efficiency Rating
SEER (Seasonal Energy Efficiency Ratio) is BTUs of cooling per watt-hour over a typical cooling season — higher SEER means less electricity for the same cooling. This table shows the same 3-ton system (36,000 BTU/hour) at different SEER ratings, at $0.16/kWh and 8 hours of daily compressor runtime. SEER2 is the updated 2023 test standard; SEER 14 ≈ SEER2 13.4.
| Efficiency | Watts | Cost per hour | Cost per month | Cost per season |
|---|---|---|---|---|
| SEER 10 (pre-2006, old systems) (baseline) | 3,500 | $0.56 | $134.40 | $672 |
| SEER 13 (2006-2015 minimum) | 3,050 | $0.49 | $117.12 | $586 |
| SEER 14 / SEER2 13.4 (current US min., new builds) | 2,900 | $0.46 | $111.36 | $557 |
| SEER 16 (high efficiency, Energy Star) | 2,550 | $0.41 | $97.92 | $490 |
| SEER 18 (two-stage) | 2,250 | $0.36 | $86.40 | $432 |
| SEER 20+ (variable-speed inverter) | 2,050 | $0.33 | $78.72 | $394 |
A SEER 10 to SEER 16 upgrade cuts the seasonal cooling bill by roughly $182 at this usage and rate. Over a 15-year system lifespan that adds up — the savings often justify the higher install cost.
Monthly Cost by Electricity Rate
Your electricity rate makes a big difference. This table shows the monthly cost of a 3-ton / 3,500W central AC across common rates, from low-cost states to high-rate states like Hawaii and the Northeast.
| Rate ($/kWh) | 4h/day | 6h/day | 8h/day | 12h/day |
|---|---|---|---|---|
| $0.10 | $42.00 | $63.00 | $84.00 | $126.00 |
| $0.13 | $54.60 | $81.90 | $109.20 | $163.80 |
| $0.16 (US avg) | $67.20 | $100.80 | $134.40 | $201.60 |
| $0.20 | $84.00 | $126.00 | $168.00 | $252.00 |
| $0.30 | $126.00 | $189.00 | $252.00 | $378.00 |
Monthly figures assume a 30-day month and the unit running at its full 3,500W. A properly sized AC cycles off whenever the house hits setpoint, so real bills run lower.
Why Central AC Costs What It Does
The compressor and condenser fan are the big draws
In a 3-ton system, the outdoor compressor draws ~2,800W, the outdoor condenser fan draws ~250W, and the indoor blower draws ~400W. Together they pull around 3,500W whenever cooling is on. When the thermostat hits setpoint, the compressor and outdoor fan shut off and only the blower briefly continues — that is why setpoint strategy matters more than any other knob.
Tonnage drives wattage, SEER drives the savings
The right tonnage matches your home's heat load — too small and the system runs non-stop; too large and it short-cycles without dehumidifying. Once tonnage is set, SEER decides how many watts you burn for each BTU of cooling. SEER 16 vs SEER 10 on the same 3-ton system saves about $182 per cooling season at the US average rate.
Duct leakage and insulation set the real ceiling
Leaky ducts in a vented attic can waste 20-30% of the cooling output before it reaches a room — the compressor runs longer to compensate, and the bill goes up proportionally. Sealing ducts and adding attic insulation often beats a SEER upgrade dollar-for-dollar over a shorter payback window.
Tips to Lower Your Cost
Set the thermostat to 78°F
Every degree warmer cuts cost by 3-5%. Going from 72°F to 78°F can save 20-30% over a cooling season with minimal comfort loss once the house is dehumidified.
Replace the filter every 1-3 months
A clogged filter chokes airflow, making the compressor run longer for the same cooling. A $10 filter swap saves 5-15% on the bill — best ROI of any AC fix.
Use ceiling fans with the AC
A fan's wind-chill effect lets you raise the thermostat 4°F with no perceived difference, cutting cooling cost by 12-20%. Turn fans off in empty rooms — they cool people, not the air.
Seal ducts and add attic insulation
Leaky ducts and an under-insulated attic can waste 20-30% of cooling output. See our energy savings guide.
Recommended picks
Central AC Cost-Cutters Worth a Look
The cheapest cooling comes from cutting compressor runtime — a smart thermostat, clean filters, and a tighter envelope all attack the runtime side of the cost equation. A SEER upgrade is the long-term play.
Smart Learning Thermostat
Cut runtime automatically
A learning thermostat sets back the AC when nobody is home and pre-cools before you return. Energy Star says programmable thermostats save 8-15% on cooling.
Variable-Speed / High-SEER Central AC
Long-term upgrade
Replacing a SEER 10 system with a SEER 16+ inverter unit cuts the cooling bill by roughly 35-50%. Pays back over a 10-15 year lifespan in most climates.
MERV 8-11 AC Filter Multi-Pack
Restore airflow
A clogged filter forces the blower and compressor to run longer for the same cooling. Replacing every 1-3 months is the cheapest efficiency upgrade you can make.
Attic Insulation & Radiant Barrier
Lower cooling load
Hot attics dump heat down into the ceiling, making the AC run longer. Adding R-30+ insulation or a radiant barrier can drop summer cooling cost by 15-25%.
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Frequently Asked Questions
How much does it cost to run central AC?
A typical 3-ton central air conditioner draws about 3,500 watts while the compressor is running. At the 2024 US average rate of $0.16/kWh, that is $0.56 per hour of compressor time. Running 8 hours a day for a 30-day summer month costs roughly $134.40. Over a 150-day cooling season at 8 hours a day, the bill comes to about $672. Real-world bills run lower because the compressor cycles off once the house hits the thermostat setpoint.
Is central AC more expensive to run than a window unit?
Per hour, yes — by 3-5x. A 3-ton central system pulls 3,000-3,800W to cool a whole house; a 1,000W window AC cools one room. If you only spend time in one or two rooms, running a window unit (and keeping the central thermostat at 82-85°F) is cheaper. But central AC cools every room evenly, dehumidifies the whole house, and is far quieter — for most households cooling 1,500+ sq ft, the per-square-foot cost ends up similar.
How do I pick the right tonnage for my house?
The rough rule of thumb is 1 ton (12,000 BTU/hour) per 500-600 sq ft of conditioned space in average climates. So a 1,500 sq ft home wants ~2.5-3 tons, a 2,000 sq ft home wants ~3-3.5 tons. Climate, insulation, ceiling height, and window area matter — a professional Manual J load calculation is more accurate than the square-foot rule. Oversized systems short-cycle, cool fast without removing humidity, and cost more to install and run.
What does SEER (or SEER2) mean for my bill?
SEER is Seasonal Energy Efficiency Ratio — BTUs of cooling delivered per watt-hour of electricity over a typical cooling season. Higher SEER = lower bill for the same cooling. A SEER 16 system uses about 35% less electricity than a SEER 10 system to cool the same house. SEER2 is the updated 2023 test standard (with more realistic airflow assumptions); SEER 14 ≈ SEER2 13.4. Current US federal minimums are SEER2 13.4 in the North and SEER2 14.3 in the South.
How many hours does central AC actually run per day?
Compressor runtime varies with weather, insulation, and thermostat setting. On a mild summer day a properly sized system might run 4-6 hours of cumulative compressor time; on a 95°F+ day, 10-14 hours. Across a full cooling season (May-September in most of the US), homeowners average 1,000-2,000 hours of compressor runtime. The cost tables on this page assume a 150-day cooling season at 8 hours of compressor time per day as a middle-of-the-road estimate.
What is the cheapest way to lower my central AC bill?
Three things, in order of payback: (1) raise the thermostat — every 1°F warmer cuts cost by 3-5%, so 78°F instead of 72°F saves 20-30%. (2) Replace the air filter every 1-3 months; a dirty filter drops airflow and makes the compressor run longer. (3) Seal duct leaks and add attic insulation — leaky ducts can waste 20-30% of cooling output. Upgrading to a higher-SEER system is the biggest single savings but only pays back over 10+ years.