How Many Watts Does a 12,000 BTU Air Conditioner Use?
A 12,000 BTU air conditioner uses 1,000 to 1,500 watts while the compressor is running, depending on its efficiency. At an EER of 10, a typical rating, it draws 1,200 watts — at most 9.6 kWh over 8 hours. The math is simple: watts = BTU per hour ÷ EER. You’ll find the EER on the unit’s EnergyGuide label.
The formula: how to work out your AC’s power use
EER (Energy Efficiency Ratio) is how many BTUs per hour the unit removes for each watt it draws, as Penn State’s energy course explains. Higher is better:
Watts = cooling capacity (BTU/h) ÷ EER
Example: a 12,000 BTU unit with an EER of 10 → 12,000 ÷ 10 = 1,200 W.
For daily use, multiply by hours: 1,200 W × 8 h = 9,600 Wh = 9.6 kWh. That is a ceiling. A conventional AC’s compressor cycles off once the room reaches the set temperature; inverter (variable-speed) models ramp down instead of switching off and use less energy, per ENERGY STAR.
Chart: AC wattage by BTU
Power draw with the compressor on, by EER:
| Capacity | EER 8 (old unit) | EER 10 (typical) | EER 12 (efficient) | 8 hours at EER 10 |
|---|---|---|---|---|
| 5,000 BTU | 625 W | 500 W | 417 W | 4.0 kWh |
| 8,000 BTU | 1,000 W | 800 W | 667 W | 6.4 kWh |
| 10,000 BTU | 1,250 W | 1,000 W | 833 W | 8.0 kWh |
| 12,000 BTU | 1,500 W | 1,200 W | 1,000 W | 9.6 kWh |
| 18,000 BTU | 2,250 W | 1,800 W | 1,500 W | 14.4 kWh |
| 24,000 BTU | 3,000 W | 2,400 W | 2,000 W | 19.2 kWh |
To estimate cost, multiply the kWh by the price per kWh on your electric bill.
How many amps does a 12,000 BTU AC draw?
Watts stay the same; the voltage changes the current. Amps = watts ÷ volts:
- 1,200 W at 115 V → about 10.4 amps.
- 1,200 W at 230 V → about 5.2 amps.
A 230 V unit doesn’t use less electricity; it just draws less current for the same power.
What size AC do I need?
ENERGY STAR’s chart (based on an 8-foot ceiling):
| Room size (sq ft) | Capacity needed |
|---|---|
| 100–150 | 5,000 BTU |
| 150–250 | 6,000 BTU |
| 250–300 | 7,000 BTU |
| 300–350 | 8,000 BTU |
| 350–400 | 9,000 BTU |
| 400–450 | 10,000 BTU |
| 450–550 | 12,000 BTU |
| 550–700 | 14,000 BTU |
| 700–1,000 | 18,000 BTU |
| 1,000–1,200 | 21,000 BTU |
| 1,200–1,400 | 23,000 BTU |
| 1,400–1,500 | 24,000 BTU |
ENERGY STAR’s adjustments: add 10% for a very sunny room (subtract 10% if heavily shaded), add 600 BTU per person beyond two, and add 4,000 BTU in a kitchen. Bigger is not better.
How to cut your AC’s energy use
Per ENERGY STAR:
- Set the thermostat as high as is comfortable, typically 78 °F.
- Keep lamps and TVs away from the AC’s thermostat; their heat makes it run longer.
- Use a fan to spread the cool air.
- Seal the unit with the insulation it came with and make sure it sits level.
Can I run a 12,000 BTU AC on a generator?
Yes, if the generator’s rated watts comfortably exceed the AC’s running watts — compressors need extra power to start, so check the manufacturer’s starting-watts figure (what size generator you need). Always run generators outdoors and at least 20 feet from windows and doors because of carbon monoxide (Ready.gov).