How Many Watts Does an Air Conditioner Use? Window vs Split vs Central
Air conditioners are the biggest power consumers in most homes. Learn exactly how many watts your AC draws based on its BTU rating and type.
The Heavy Hitters of Home Energy
When the summer heat sets in, air conditioners become the undisputed kings of electricity consumption in a residential home. Depending on the type and size of the unit, an air conditioner can use anywhere from 500 watts for a small window unit to over 5,000 watts for a large central air system.
Because AC units consume so much power, understanding their wattage is critical for managing your summer utility bills, sizing a solar array, or determining what size generator you need for backup power.
Air Conditioner Wattage by Type and BTU
Air conditioners are rated by their cooling capacity, measured in BTUs (British Thermal Units) or Tons (1 Ton = 12,000 BTU). The higher the cooling capacity, the more electrical watts the unit will require to operate the compressor and blower fans.
| AC Type | Cooling Capacity | Running Watts | Starting Watts |
|---|---|---|---|
| Small Window AC | 5,000 - 6,000 BTU | 500W - 600W | 1,500W - 1,800W |
| Medium Window AC | 8,000 - 10,000 BTU | 700W - 1,000W | 2,100W - 3,000W |
| Large Window / Portable AC | 12,000 - 14,000 BTU | 1,200W - 1,500W | 3,600W - 4,500W |
| Mini-Split (Ductless) | 12,000 BTU (1 Ton) | 900W - 1,200W | Variable (Inverter) |
| Central AC (Small Home) | 24,000 BTU (2 Ton) | 2,000W - 2,500W | 6,000W - 7,500W |
| Central AC (Large Home) | 48,000 BTU (4 Ton) | 4,000W - 5,000W | 12,000W - 15,000W |
Why Mini-Splits Use Fewer Starting Watts
If you look at the chart above, you'll notice that Mini-Split systems have a "Variable" starting wattage. This is because modern ductless mini-splits use inverter technology.
Instead of slamming the compressor on at 100% power (which causes a huge wattage spike), an inverter slowly ramps up the compressor's speed. This virtually eliminates the starting surge, making mini-splits incredibly easy to run on small generators or solar battery banks.
How to Calculate Your AC's Operating Cost
To figure out how much your air conditioner costs to run, you need to know its running wattage, how many hours a day it runs, and your local electricity rate.
Worked Example: 10,000 BTU Window AC
Let's say you have a 10,000 BTU window unit that draws 900 watts. You run it for 8 hours a day during the summer, and your electricity costs $0.15 per kWh.
- Calculate Daily Watt-Hours: 900 watts × 8 hours = 7,200 watt-hours.
- Convert to Kilowatt-Hours (kWh): 7,200 / 1,000 = 7.2 kWh per day.
- Calculate Daily Cost: 7.2 kWh × $0.15 = $1.08 per day.
- Monthly Cost: $1.08 × 30 days = $32.40 per month.
EER and SEER Ratings Explained
When shopping for an AC, you'll see efficiency ratings like EER (Energy Efficiency Ratio) or SEER (Seasonal Energy Efficiency Ratio). These numbers tell you how much cooling (BTU) you get per watt of electricity used.
For example, a 12,000 BTU air conditioner that uses 1,000 watts has an EER of 12. A higher EER or SEER rating means the unit produces more cooling using fewer watts, which directly translates to lower electricity bills.
Generator Sizing for Central Air Conditioners
Running a central air conditioner during a power outage is a common goal, but it requires a substantial generator. A 3-ton (36,000 BTU) central AC typically draws around 3,500 running watts, but its starting surge can exceed 10,000 watts.
To run a central AC on a portable generator, many homeowners install a Soft Start Kit. A soft starter is a device wired into the AC condenser that reduces the starting surge by up to 70%, allowing you to start a 3-ton AC on a much smaller 5,000W or 7,000W generator.