How much electricity an air conditioner uses by type and BTU, how to estimate running cost, and easy ways to lower your bill.
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A typical window air conditioner uses between 500 and 1,500 watts per hour depending on its BTU rating and efficiency. A central air system draws 3,000 to 5,000 watts. Translated to running cost at the US average electricity rate of about 16 cents per kWh: a 12,000 BTU window unit with a CEER of 12 costs roughly 16 to 18 cents per hour to run, or about 1.25 to 1.50 dollars for an 8-hour day. Our best air conditioners guide highlights the most efficient options at each BTU level to help keep those costs down.
The exact number depends on three things: how large the unit is (BTU), how efficient it is (CEER or SEER2 rating), and how many hours per day it actually runs. A well-sized, properly installed unit in a well-insulated room runs fewer hours than an undersized unit struggling to keep up, which matters as much as the efficiency rating itself.
Below is a breakdown by type, BTU range, and real-world usage patterns, followed by a simple formula so you can estimate your own number. For the sizing foundation, see the air conditioner BTU chart.
| AC Type | BTU Rating | Typical Wattage | Est. Cost per 8-hr Day* |
|---|---|---|---|
| Window unit | 5,000 BTU | 400 to 500W | $0.50 to $0.65 |
| Window unit | 8,000 BTU | 640 to 800W | $0.80 to $1.05 |
| Window unit | 12,000 BTU | 900 to 1,200W | $1.15 to $1.55 |
| Window unit | 18,000 BTU | 1,400 to 1,800W | $1.80 to $2.30 |
| Portable unit | 12,000 BTU | 1,000 to 1,400W | $1.30 to $1.80 |
| Mini-split (single zone) | 12,000 BTU | 700 to 900W | $0.90 to $1.15 |
| Mini-split (single zone) | 24,000 BTU | 1,500 to 2,000W | $1.90 to $2.55 |
| Central air system | 24,000 to 60,000 BTU | 3,000 to 5,000W | $3.85 to $6.40 |
*Estimates at 16 cents per kWh, assuming the unit runs for the full 8 hours. Actual run time varies by room conditions. For efficiency-focused picks see the best energy efficient air conditioners.
The formula is straightforward:
Cost per hour = (Wattage / 1,000) x your electricity rate in dollars per kWh
To find wattage from a BTU and CEER rating: Watts = BTU / CEER. A 12,000 BTU unit with CEER 12 draws 1,000 watts. At 16 cents per kWh that is 16 cents per hour. Running 8 hours per day for 90 days is 720 hours, costing about 115 dollars for the season. The same unit with CEER 15 draws 800 watts and costs about 92 dollars — a saving of roughly 23 dollars over the season. Check your electricity bill for your local rate; it varies from about 10 cents in some states to over 28 cents in Hawaii and parts of the Northeast.
The table below estimates seasonal cost for a 12,000 BTU window unit running 8 hours per day for 90 days (one summer), at both CEER 10 and CEER 14, across a range of state electricity rates.
| Electricity Rate (cents/kWh) | CEER 10 (1,200W) — Season | CEER 14 (857W) — Season | Saving over season |
|---|---|---|---|
| 10 cents (e.g., Louisiana) | $86.40 | $61.70 | $24.70 |
| 14 cents (US midrange) | $120.96 | $86.41 | $34.55 |
| 16 cents (US average) | $138.24 | $98.78 | $39.46 |
| 22 cents (California) | $190.08 | $135.82 | $54.26 |
| 29 cents (Hawaii / NE peak) | $250.56 | $178.95 | $71.61 |
In states with high electricity rates, choosing a CEER 14 unit over a CEER 10 unit can save 50 to 70 dollars per summer on a single 12,000 BTU window unit. Over 5 to 8 years that difference exceeds the typical price premium for a higher-efficiency model.
CEER (Combined Energy Efficiency Ratio) applies to window and portable units. A higher number means fewer watts drawn per BTU of cooling. Energy Star-certified window units require CEER 12 or higher. Units reaching CEER 14 to 15 are among the most efficient in the window category. The difference between CEER 10 and CEER 14 on a 12,000 BTU unit is 343 watts per hour — meaningful over a summer.
SEER2 applies to mini-splits and central systems. The minimum new-install SEER2 in the US is around 13 to 15 depending on region. High-efficiency mini-splits reach SEER2 20 to 30+. A SEER2 20 unit uses about 33% less electricity than a SEER2 15 unit for the same cooling output. Over 10 to 15 years (typical mini-split lifespan), that difference adds up significantly. The best mini-split air conditioners covers high-SEER2 options.
An AC only draws significant power when the compressor is running. Modern units with inverter compressors (common in mini-splits, increasingly in window units) modulate compressor speed rather than cycling fully on and off, which reduces electricity draw during partial-load conditions and makes them noticeably quieter. See the best quiet air conditioners for options where the noise-efficiency link matters most.
Fan-only mode uses roughly 5 to 20% of the electricity that cooling mode uses. If outdoor temperature drops at night, running fan-only instead of cooling can save significantly while still moving air through the room. Sleep mode on many modern units raises the set temperature by 1 to 2 degrees over 8 hours, reducing compressor run time through the night without waking you with temperature changes.
Many window units draw 1 to 5 watts even when off but plugged in, due to the control board, display, and Wi-Fi module staying active. Over a year of being left plugged in (even seasonally), this can add a few dollars to your electricity bill. Units with a true mechanical on/off switch eliminate this. CEER ratings include this standby draw in their calculation, so a unit with a high CEER already accounts for standby consumption — another reason CEER is a more complete efficiency measure than older EER ratings which excluded standby.
Right-sizing is the most impactful step. A properly sized unit reaches the set temperature in a reasonable time and then cycles off — it does not run continuously. An undersized unit running non-stop uses far more electricity than a correctly sized one with a reasonable duty cycle. Use the air conditioner BTU chart to check your current unit is sized correctly before assuming efficiency improvements are needed.
Setting the thermostat to 78 degrees Fahrenheit rather than 72 degrees cuts energy use by roughly 6 to 8% per degree in most conditions. Pre-cooling during off-peak utility rate hours (often overnight or mid-morning) and then letting the unit coast is effective in areas with time-of-use pricing. Keeping filters clean maintains airflow and prevents the unit from working harder than it needs to — a clogged filter can raise electricity use by 5 to 15%. Shading west-facing windows with blinds or curtains during afternoon hours reduces the heat load the unit has to handle.
Running ceiling fans in the same room allows you to raise the thermostat set point by 2 to 4 degrees without reducing perceived comfort — the moving air increases evaporation from skin. The fan itself uses 10 to 75 watts depending on size and speed, a fraction of what the AC compressor draws, so the net effect is positive as long as you actually raise the thermostat.
Mini-splits are the most efficient option for any fixed installation. They use inverter compressors, have the highest SEER2 ratings, and place the compressor outside where it does not add to the room heat load. Window units are the middle ground — efficient enough for most residential use, especially Energy Star models. Portable units are the least efficient because the compressor inside the room adds heat that the unit must then remove. For the same BTU output, a portable unit typically uses 15 to 30% more electricity than a window unit. If you want the maximum efficiency per dollar of operating cost for a single room, window units beat portables consistently.
For the best options across all types, organized by BTU and efficiency, see the best air conditioners ranking. The best window air conditioners and best portable air conditioners guides note CEER ratings for every model covered so you can run the numbers for your specific usage.
Understanding your running cost makes sizing decisions easier and helps you weigh the tradeoff between a higher upfront cost for a more efficient model and the lower operating cost over several summers. The best air conditioners ranking notes CEER and SEER2 ratings for every model covered so you can run the numbers for your specific usage.
A 12,000 BTU window unit with a CEER of 12 costs roughly 1.15 to 1.55 dollars for 8 hours of running at the US average electricity rate of about 16 cents per kWh. A smaller 8,000 BTU unit costs closer to 0.80 to 1.05 dollars for the same period. Your actual cost depends on your local electricity rate and how often the compressor cycles.
Yes. More BTU means more cooling capacity, which requires more watts. However, a higher-BTU unit that is correctly sized for the room may run fewer hours than an undersized unit running constantly, so total daily electricity use depends on both the unit size and how well it matches the room.
Generally yes. Mini-splits use inverter compressors and carry higher SEER2 efficiency ratings than most window units. For a comparable BTU output, a high-efficiency mini-split typically uses 20 to 40% less electricity than a window unit over a cooling season. The upfront cost is higher, but operating savings reduce the gap over several years.
The biggest levers are: right-sizing your unit so it does not run constantly, setting the thermostat to 78 rather than 72 degrees, keeping the air filter clean, shading west- and south-facing windows during afternoon hours, and using sleep mode at night. Pre-cooling during off-peak rate hours also helps in areas with time-of-use electricity pricing.
Divide the unit's wattage by 1,000 to get kilowatts, then multiply by the hours per day it runs, then by the number of days. Example: a 1,000W unit running 8 hours a day for 30 days = 240 kWh per month. Multiply by your electricity rate per kWh to get the dollar cost. The wattage is usually on the nameplate label or in the manual; you can also calculate it as BTU divided by CEER.
Fan-only mode uses roughly 50 to 200 watts depending on fan size, compared to 700 to 1,500 watts when the compressor is running. Running the fan continuously between cooling cycles does add to your bill but the cost is small compared to compressor run time. A better strategy is to let the unit cycle normally on auto fan, which reduces both electricity use and humidity more effectively than running the fan continuously.
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