How Much Does It Cost to Run a Window AC?
A mid-size window air conditioner draws about 900W while the compressor runs. At the 2024 US average of $0.16/kWh that is $34.56 a month at 8 hours of cooling a day, or $138.24 across a 4-month summer. The calculator opens on exactly that unit — 900W, 8 hours a day — so change the wattage, the runtime or your state and every figure follows.
Only know the BTU? Pick the capacity and efficiency and we'll fill in the watts.
10,000 ÷ 11 = 909W
Daily Cost
$1.15
7.2 kWh
Monthly Cost
$34.56
216.0 kWh
4-month season Cost
$138.24
864.0 kWh
8 hours of compressor time is roughly 12 hours switched on
A unit sized to its room reaches setpoint and the compressor stops while the fan keeps turning. So the figures above are what a thermostat leaves you with after a 12-hour day — not the cost of 12 hours at full power, which would be $53.17 a month. Set the hours to what the compressor runs, not what the switch does.
The same cooling from a portable would draw about 1,082W — $27.99 more this season
A single-hose portable blows conditioned room air out of the window, so warm outdoor air leaks back in to replace it, and its compressor sits in the room it is trying to cool. If a standard window will take a unit, the window unit is the cheaper machine to run. Full portable AC costs.
Monthly figures use a 30-day month and the season a 4-month cooling season. Wattage is the compressor-plus-fan draw while cooling; the fan alone uses a few dozen watts once the compressor cycles off. Rates are 2024 state averages — pick your state above or see electricity rates by state.
Don't know your unit's wattage? It is the BTU rating divided by the EER on the yellow EnergyGuide sticker — the BTU-to-watts table below does the division for every common size. For a different appliance entirely, use the appliance cost calculator.
Summer Season Cost Table
What a window unit adds to the bill, by how much it draws and how long it runs. The season column is 4 months — roughly June through September — at the US average of $0.16/kWh. Hours are compressor hours, not hours with the switch on; a right-sized unit cycles off once the room hits setpoint, so 8 hours of cooling here is about 12 hours of the unit being switched on.
| Hours per day | Small · 500W4,500–6,000 BTU | Typical · 900W8,100–10,800 BTU | Large · 1,440W12,960–17,280 BTU | |||
|---|---|---|---|---|---|---|
| per month | season | per month | season | per month | season | |
| 4hEvenings only | $9.60 | $38 | $17.28 | $69 | $27.65 | $111 |
| 8hA working day | $19.20 | $77 | $34.56 | $138 | $55.30 | $221 |
| 12hMost of the day | $28.80 | $115 | $51.84 | $207 | $82.94 | $332 |
The highlighted cell is the calculator's starting point. Read across it and the shape of the bill is clear: doubling the runtime doubles the cost exactly, and so does trading a bedroom unit for a great-room one. Nothing about a window AC is non-linear — which is why the two levers that matter are the size you buy and the hours you let it run.
BTU to Wattage Reference
A BTU rating tells you how much heat the unit can move, not how much electricity it takes to move it. The EER on the yellow EnergyGuide sticker is the bridge: watts = BTU ÷ EER. Two units with the same number on the box can be 200W apart, so find your BTU row and then read across to the efficiency you actually own.
| Capacity | Room it suits | EER 9Pre-2014 units and the cheapest imports | EER 11Roughly the floor for a new unit today | EER 12Energy Star and inverter models | Season gapEER 9 vs 12 |
|---|---|---|---|---|---|
| 5,000 BTUup to ~250 sq ft | Small bedroom or home office | 556W | 455W | 417W | $21 |
| 6,000 BTUup to ~300 sq ft | Bedroom | 667W | 545W | 500W | $26 |
| 8,000 BTUup to ~400 sq ft | Main bedroom or small living room | 889W | 727W | 667W | $34 |
| 10,000 BTUup to ~500 sq ft | Living room | 1,111W | 909W | 833W | $43 |
| 12,000 BTUup to ~600 sq ft | Large living room | 1,333W | 1,091W | 1,000W | $51 |
| 15,000 BTUup to ~750 sq ft | Open-plan great room | 1,667W | 1,364W | 1,250W | $64 |
| 18,000 BTUup to ~900 sq ft | A whole floor of a small apartment | 2,000W | 1,636W | 1,500W | $77 |
Room sizes use the standard sizing rule of about 20 BTU per square foot of insulated floor area. The season gap is what the efficiency spread costs over 4 months at 8 hours a day and $0.16/kWh — for most sizes it is larger than the price difference between the two units on the shelf, and it repeats every summer.
The Formula
Cost = (watts ÷ 1,000) × compressor hours × 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. The one place people go wrong is the hours: they should be hours of compressor runtime, not hours the unit is plugged in. Once the room reaches setpoint the compressor stops and only the fan keeps turning, on roughly 60W.
Worked example (900W window AC, 8 h/day, 30 days, $0.16/kWh): (900 ÷ 1,000) × 8 × 30 × 0.16 = 0.9 kW × 240 hours × $0.16 = $34.56 per month. That is $1.15 a day, $138.24 a summer, and $420 if you somehow ran it year-round.
What the Season Costs by Region
Identical unit, identical runtime, different bill. The same 900W window AC at 8 hours a day costs $106 a season in the West South Central division and $224 in New England — 2.1× the money for the same cool room.
| Census division | Average rate | Per month | 4-month season | Cheapest / dearest state |
|---|---|---|---|---|
| West South CentralTexas is the big grid here; Arkansas, Louisiana and Oklahoma are cheaper still. | $0.123 | $26.47 | $106 | Arkansas $0.11 / Texas $0.14 |
| East South CentralKentucky and Tennessee anchor the cheap end of the map. | $0.125 | $26.96 | $108 | Kentucky $0.12 / Alabama $0.14 |
| MountainIdaho and Utah have the cheapest power in the country; Colorado the priciest in the division. | $0.126 | $27.19 | $109 | Idaho $0.10 / Colorado $0.15 |
| West North CentralPlains and Upper Midwest — every state here is under the national average. | $0.132 | $28.43 | $114 | North Dakota $0.12 / Minnesota $0.14 |
| South AtlanticNine jurisdictions from Florida to Delaware, all of them below the national average. | $0.138 | $29.78 | $119 | North Carolina $0.12 / Maryland $0.16 |
| East North CentralThe Great Lakes states, clustered a few cents either side of $0.15. | $0.155 | $33.58 | $134 | Indiana $0.14 / Michigan $0.18 |
| Middle AtlanticNew York prices near $0.22 while Pennsylvania sits close to the middle of the country. | $0.188 | $40.71 | $163 | Pennsylvania $0.17 / New York $0.22 |
| PacificThe widest spread of any division — Washington hydro at one end, Hawaii's oil-fired island grid at the other. | $0.229 | $49.55 | $198 | Washington $0.11 / Hawaii $0.39 |
| New EnglandSix states, not one of them priced below the national average. | $0.260 | $56.09 | $224 | Vermont $0.21 / Connecticut $0.29 |
Divisions are the US Census Bureau's nine, and each rate is an unweighted average of the member states — every state counts once, however many people live in it. Notice which way the table runs: the three divisions that keep an AC on longest — West South Central, East South Central and the South Atlantic — are all in the cheapest five, which is the one piece of good news about a long cooling season. Your own state is the number to use, not the division — look it up in electricity rates by state or pick it in the calculator above.
Where a Window AC Sits in the Summer Bill
A portable needs about 1,082W for the same cooling
A single-hose portable exhausts conditioned room air out of the window, so warm outdoor air leaks back in to replace it, and it keeps its compressor in the room it is cooling. Matching this 900W window unit costs about $166 a season against $138 — $28 more, every summer, for the same room. Worth it only when a casement or sliding window rules a proper unit out. Portable AC costs by BTU.
The window AC is rarely the whole increase
A window AC is rarely the only thing that changed between April and July. Central air, a pool pump left on a factory 8-hour schedule and a refrigerator working harder in a hot kitchen usually account for most of the increase, and they are worth ruling out before you blame the unit in the bedroom. The biggest energy wasters in summer puts a monthly figure on each of them.
Three window units is a central AC
One 900W unit undercuts a 3,500W central system by a wide margin — but that is a statement about cooling one room, not about the technology. Three of them running at once draw 2,700W and cost $104 a month, which is central-air territory. Window units save money by letting you cool fewer rooms. Central AC cost by tonnage and SEER.
Why Window ACs Cost What They Do
The compressor is the energy hog
A window AC's fan draws around 60W. The compressor — which actually moves heat out of the room — accounts for the rest. When the room hits the thermostat setpoint the compressor shuts off and only the fan keeps running, which is why a one-degree-higher setpoint can cut runtime by 5-10% and why the hours in every table above are compressor hours.
EER is more important than BTU
EER tells you BTUs of cooling per watt of electricity, so it is the divisor that turns a capacity into a bill. A 10,000 BTU unit at EER 12 uses about 833W; the same cooling at EER 9 uses 1,111W — a third more electricity for an identical room. Look for EER 11 or higher and the blue Energy Star label.
Sizing matters as much as efficiency
An oversized AC cools the air fast but shuts off before it can dehumidify, so the room feels clammy and you set the thermostat lower to compensate. An undersized unit never reaches setpoint and runs full-blast all day — the one case where the nameplate wattage really is what you pay. About 20 BTU per square foot is a reasonable starting point for an insulated room.
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% a month with little comfort loss after the room is dehumidified.
Clean the filter monthly
A clogged filter cuts airflow, making the compressor run longer to remove the same heat. Five minutes of cleaning saves 5-15% on the bill.
Block direct sun on the window
Closing blinds or installing reflective film on the AC's own window prevents solar heat gain and cuts runtime by 15-25% on hot afternoons.
Seal the side panels
Foam strips or insulated panels around the unit stop hot, humid air from leaking in. See our energy savings guide.
Recommended picks
Window AC Upgrades Worth a Look
The cheapest cooling comes from the right size unit, a high EER, and a thermostat or smart plug. These categories all attack the runtime side of the cost equation.
Inverter Window Air Conditioner
Variable-speed compressor
Inverter models ramp the compressor up and down instead of cycling fully on and off, using 30-40% less electricity than a comparable fixed-speed unit.
Energy Star Window AC with Smart Plug
Schedule + thermostat
Energy Star units use about 10% less power than standard models. Wi-Fi or smart-plug control lets you cool only when you are home.
Insulated Window AC Side Panels
Reduce leakage
Most cooling loss in a window unit happens around the flimsy accordion side panels. Foam-insulated panels stop hot air from leaking in around the unit.
Reflective Window Film
Lower cooling load
Blocking direct sun on a south- or west-facing window can cut the AC's runtime by 20-30% on hot afternoons. Cheaper than upgrading the unit.
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Related Guides
Cost to Run a Portable Air Conditioner
When a window unit won't fit the window
Biggest Energy Wasters in Summer
What else is driving the July bill
Cost to Run Central AC
Whole-home cooling by tonnage and SEER
Cost to Run a Dehumidifier
Running one in a cooled room does the job twice
Cost to Run a Ceiling Fan
The cheapest way to raise the setpoint
Electricity Rates by State
Find your state's average rate
Most Efficient Appliances
See which appliances cost the most to run
How to Save on Energy Bills
Practical tips by room with savings
Energy Star Guide
Is upgrading worth the cost?
Frequently Asked Questions
How much does it cost to run a window AC?
A mid-size window AC draws about 900W while the compressor runs — that is an 8,100 BTU unit at the bottom of the efficiency band or a 10,800 BTU one at the top. At the 2024 US average rate of $0.16/kWh that is $0.14 an hour, $34.56 for a 30-day month at 8 hours of compressor time a day, and $138.24 across a 4-month cooling season. Hours mean compressor hours: a right-sized unit reaches setpoint and cycles off, so 8 hours of cooling is closer to 12 hours with the switch on.
How do I convert BTU to watts?
Divide the BTU rating by the EER printed on the yellow EnergyGuide label: watts = BTU ÷ EER. An 8,000 BTU unit is 889W at EER 9 and 667W at EER 12 — the same cooling for a third less electricity. That is why BTU alone tells you almost nothing about the bill. If you cannot find an EER, assume around 11 for a unit bought in the last decade and around 9 for anything older.
Does setting it higher really save money?
Yes, more than people realize. Every degree warmer you set the thermostat cuts cooling cost by roughly 3-5%, because the compressor cycles off sooner and runs fewer minutes per hour. Setting 78°F instead of 72°F can lower the monthly AC bill by 20-30% with most people not noticing the difference once the room is dehumidified.
What does the EER rating mean for cost?
EER (Energy Efficiency Ratio) is BTUs of cooling per watt of electricity, so it is the divisor in the wattage sum. A 10,000 BTU unit at EER 12 draws 833W; the same cooling at EER 9 draws 1,111W. Over a 4-month season at 8 hours a day that gap is $43 at the US average rate. Look for EER 11 or higher and the blue Energy Star label.
Is a window AC cheaper to run than central air?
For cooling one room, yes — by a lot. Central AC pulls 3,000-5,000W to cool the whole house. Running one 900W window unit in the room you actually use costs a third to a fifth as much per hour. The catch is comfort: window units only cool the room they are in, and three of them running at once draw about what a central system does. For a small home, or one person spending most of the day in one space, a window unit is the cheapest cooling there is.