What does a room air conditioner cost to run?
Size drives almost everything: a whole-floor unit costs about four times a bedroom unit.
Every figure below is computed from the catalogue, not written by hand · updated October 19, 2026
Cost by size
| What it is | kWh a year | Cost a year |
|---|---|---|
| Under 8,000 BTU — a small bedroom57 models | 326 | $59 |
| 8,000–12,000 BTU — a bedroom or small living room208 models | 454 | $82 |
| 12,000–18,000 BTU — a large living room173 models | 639 | $115 |
| Over 18,000 BTU — a whole floor58 models | 1,204 | $217 |
Priced a year at the U.S. average residential rate.
These are annual figures, which for an air conditioner is effectively a cooling season: the certified energy use assumes the machine runs during cooling weather and sits idle the rest of the year.
Buying bigger than you need costs you twice
The table above is the strongest argument against over-sizing. Stepping from a 10,000 BTU unit to an 18,000 BTU unit roughly doubles the running cost, every season, for as long as you own it.
An oversized unit also cools worse. It drops the room temperature fast, satisfies the thermostat, and shuts off before it has pulled much moisture out of the air — so the room ends up cold and clammy, and the compressor short-cycles. Matching the unit to the room is the single decision that most affects both comfort and cost.
Within one size, the spread is still large
Among the 208 certified units in the most common size band, the most efficient uses 375 kWh and the least efficient 640 kWh — a difference of $48 a year between two air conditioners that cool the same room.
The figure that separates them is CEER, the combined energy efficiency ratio, which runs from 12 to 17.6 across the 496 models we hold. Higher is better, and the gap between the ends of that range is what the figures above are made of.
What the figure assumes
The certified energy use comes from the federal test procedure, which runs every unit through the same conditions. Your own cost moves with how hot your summer is, what temperature you set, how well the room is insulated, and how many hours a day the unit actually runs. A unit in Phoenix and the same unit in Portland will not cost the same.
Price any certified room air conditioner at your state's rate, or enter the rate from your own bill for a figure matched to what you actually pay.
Where these numbers come from
Averages across every ENERGY STAR certified room air conditioner we hold, grouped by cooling capacity. The certified figure is annual, which for a seasonal machine is effectively one cooling season.
Costs are that energy use multiplied by a state's average residential electricity price from the U.S. Energy Information Administration. Change the state above and every figure on this page moves with it. Full methodology.
Compare every certified room air conditioner by running cost