Window ACs use about 420 to 1,800 watts. A 12,000 BTU window air conditioner requires 1000 to 1200 watts when the unit is one of the most common efficiencies from 10 to 12 EER.
The number of watts your window air conditioner uses depends on several factors:
- Energy Efficiency Ratio (EER) rating
- Your specific air conditioner model
- The size of your air conditioner
- Room size
- How old your air conditioner is – And how well it is maintained
Per hour – but not every hour! If your window air conditioner ran all the time, it would use the full wattage it is rated for.
But window air conditioners run in cycles throughout the day, turning on and off two or three times each hour. This on-and-off cycle can make a 1000-watt window air conditioner use no more than 650 watts per hour, for example.
What is a low wattage window air conditioner?
On average, a low wattage window air conditioner is one that uses less than 500 watts to 1,000 watts based on the BTU capacity of the unit. In other words, 1,000 is low watts for a 12,000 BTU AC, but not for one with less capacity than that.
Key: Regardless of BTU output, a low wattage window AC is one that is energy efficient. These are the most energy efficient window ACs in each size class.
The lowest wattage window air conditioner consumes a little more than 400 watts, and the highest is approximately 2,400 watts.
To know more about your window unit’s wattage and if your generator can support your unit during a power outage, refer to the rest of our article below.
How Many Watts Does a Window Air Conditioner Use?
To figure this out, you first need to understand two important units of measurement used for air conditioners:
BTU measures how much energy is used to heat or cool a pound of water by one degree Fahrenheit. In other words, it is the air conditioner’s cooling capacity. EER, on the other hand, indicates how much power the air conditioner consumes (in watts). The larger the BTU, the bigger the air conditioner and the more wattage is required. The higher the EER rating, the less wattage the unit uses over time.
AC Size to Wattage Chart
| Window AC Size | 10 EER AC | 11 EER AC | 12 EER AC |
| 5000 BTU | 500 Watts | 455 Watts | 417 Watts |
| 6000 BTU | 600 Watts | 545 Watts | 500 Watts |
| 7000 BTU | 700 Watts | 636 Watts | 583 Watts |
| 7500 BTU | 750 Watts | 682 Watts | 625 Watts |
| 8000 BTU | 800 Watts | 727 Watts | 667 Watts |
| 10000 BTU | 1000 Watts | 909 Watts | 833 Watts |
| 12000 BTU | 1200 Watts | 1091 Watts | 1000 Watts |
| 13500 BTU | 1350 Watts | 1227 Watts | 1125 Watts |
| 14000 BTU | 1400 Watts | 1273 Watts | 1167 Watts |
| 18000 BTU | 1800 Watts | 1636 Watts | 1500 Watts |
If you own a 5,000 BTU unit with a 10 EER rating, for example, then your unit will run on 500 watts. By comparison, if you own a unit with a 12 EER rating and the same BTU, it will only need 417 watts to run. This is due to the higher energy efficiency of 12 EER vs. 10 EER.
In short, watts are equal to BTU divided by the EER rating.
For example, 5,000 BTU / 10 EER = 500 watts.
The catch here is that our chart and the equation present the running wattage for your unit. This is only half of the equation, so to speak. To know if your generator will power your window air conditioner, you will also need to know the surging wattage, which we detail below.
Running Watts vs. Surging Watts
Surging wattage—or, what some call starting wattage—is the power required to start up the air conditioner. Running wattage is the amount of energy required to keep the unit on and working.
Air conditioner compressors need more power to start than they do to keep running. As a rule, surging wattage is 3.8 to 4.8 times more than running wattage, which means your generator will need to support the sum of the surging and running watts.
Factoring in both of these, here is a rough estimate of the generator size you need depending on your air conditioner size:
- A 417-to-500-watt unit (5,000 BTU) will require a 2,000-watt generator.
- A 550-to-1,000-watt unit (5,000-10,000 BTU) will require a 2,500-3,000-watt generator.
- A 1,000-to-1,400-watt unit (10,000-14,000 BTU) will require a 3,000-4,000-watt generator.
- A 1,400-to-1,800-watt unit (14,000-18,000 BTU) will require a 4,000-6,000-watt generator.
Will A 2000 Watt Generator Run A Air Conditioner?
| AC Cooling Capacity | 10 EER AC | 11 EER AC | 12 EER AC | 15 EER AC |
| 5000 BTU | Yes | Yes | Yes | Yes |
| 6000 BTU | Maybe | Probably Yes | Yes | Yes |
| 7000 BTU | No | No | Probably Yes | Yes |
| 7500 BTU | No | No | No | Yes |
| 8000 BTU | No | No | No | Yes |
| 10000 BTU | No | No | No | No |
| 12000 BTU | No | No | No | No |
Will a 2,000-watt generator run an 8,000 BTU window air conditioner? In most cases, no. Units with such high cooling capacity will not be supported by a generator that small, as the surging watts will overwhelm it. The only exception to this is when the air conditioner has a 15 EER rating, which is rare. There are only a few ACs that meet that efficiency level, and they all have variable capacity compressors.
Will a 2000 watt generator run a 5000 btu air conditioner?
Yes. A 2000-watt generator will run a 5,000 BTU window air conditioner between 10 EER and 15 EER without any trouble.
Tip – We are using surging watts = 4X running watts for the determination. It could be higher or slightly lower.
Will A 3,500-Watt Generator Run a Window AC?
A 3,500-watt generator can support any window air conditioner between 5,000 BTU with a 10 EER rating and 10,000 BTU with a 15 EER rating.
A generator this size can run a 12,000 BTU air conditioner rated 15 EER, given the unit’s high energy efficiency, but it is questionable how much support it will provide less efficient 12,000 BTU units, not to mention 13,000 BTU. It would be safer to use a larger generator to guarantee no issues with your generator.
| AC Cooling Capacity | 10 EER AC | 11 EER AC | 12 EER AC | 15 EER AC |
| 5000 BTU | Yes | Yes | Yes | Yes |
| 6000 BTU | Yes | Yes | Yes | Yes |
| 8000 BTU | Yes | Yes | Yes | Yes |
| 10000 BTU | Probably Yes | Yes | Yes | Yes |
| 12000 BTU | Maybe | Maybe | Probably Yes | Yes |
| 13500 BTU | No | Maybe | Maybe | Maybe |
| 14000 BTU | No | No | No | No |
| 18000 BTU | No | No | No | No |
| 24000 BTU | No | No | No | No |
The ratings considered here are surging wattage of 3,900 to 4,200 watts. The average surging or starting watts capacity for a generator listed as 3,500 watts is 4,200 watts. Generators are listed/sold by running watts, not their high-capacity watt potential.
Something to keep in mind: While our chart shows that a 3,500-watt generator can power window air conditioners below 12,000 BTU, this does not mean that you should use such a high-powered generator for all air conditioners below this BTU. Generators that are too large will not work to their full potential, being less energy-efficient and costing you extra money on fuel. Therefore, we advise using a smaller generator for air conditioners between 5,000 BTU and 10,000 BTU.
Will A 5,000-Watt Generator Run My Window Air Conditioner?
A 5,000-watt generator can support any air conditioner within 5,000 BTU and 12,000 BTU with a 9-12 EER rating. It can also support 13,500 BTU and 14,000 BTU units with an 11 or 12 EER rating, while possibly being able to run units with the same BTU but a 10 EER rating. Above 14,000 BTU, you will need a larger generator.
| AC Cooling Capacity | 9 EER AC | 10 EER AC | 11 EER AC | 12 EER AC |
| 5000 BTU | Yes | Yes | Yes | Yes |
| 6000 BTU | Yes | Yes | Yes | Yes |
| 8000 BTU | Yes | Yes | Yes | Yes |
| 10000 BTU | Yes | Yes | Yes | Yes |
| 12000 BTU | Yes | Yes | Yes | Yes |
| 13500 BTU | Maybe | Probably Yes | Yes | Yes |
| 14000 BTU | No | Probably Yes | Yes | Yes |
| 18000 BTU | No | No | No | Maybe |
| 24000 BTU | No | No | No | No |
