- The cooling capacity of the AC unit, which is measured in BTU/hour.
- The Energy Efficiency Ratio (EER), which is similar to the gas mileage value of a car. Air conditioners with a higher EER use less electricity.
Generally, window air conditioners use between 500 and 2,000 watts per hour. Window air conditioners with a cooling capacity below 10,000 BTU/h will generally have a power consumption of fewer than 1,000 watts unless you have an old and inefficient unit. On the other hand, a larger AC with a capacity of over 20,000 BTU/h can exceed 2,000 watts.
Powering an air conditioner with a solar generator is possible, as long as the power output of the generator is higher than the power input of the AC. For example, a solar generator with an output of 2,000W will be capable of powering a small conditioner using 700W, but not a central AC unit consuming 2,500W.
Understanding Key Terms: BTU, Rated Watts, Running Watts, and Watt-Hours
Before discussing the energy usage of window air conditioners, it’s important to understand the technical terms used to describe their consumption.
BTU (stands for British Thermal Unit)
BTUs are used to measure the cooling output of air conditioners, and also the heating output of furnaces and heat pumps. One BTU is the amount of heat you must remove to lower the temperature of one pound of water by 1°F. Small ACs for individual rooms have a typical capacity of less than 12,000 BTU/h, while central units that cool an entire home can reach 60,000 BTU/h.
Rated Watts
The rated wattage of an air conditioner is the electricity input consumed when the unit runs at full cooling capacity. For example, you may find a 12,000 BTU/h window AC with a rated wattage of 1,200W.
Running Watts
Air conditioners don’t always operate at full capacity. When the weather is mild and you don’t need the maximum cooling capacity of an AC, its power input is also reduced. The rated wattage is what the AC unit uses when running at full capacity, while the running wattage describes the real consumption at a given time.
Watt-Hours
Watts describe the instantaneous power consumption of air conditioners, while watt-hours (Wh) describe the accumulated consumption over time. A window AC using 1,000 watts during 6 hours will consume 6,000 watt-hours. Electric companies bill you in kilowatt-hours, where 1 kWh = 1,000Wh.
Using these technical concepts, discussing the energy consumption of air conditioners becomes much easier.
How Much Power Does a Window AC Use?
Home air conditioners can be classified into two main types: window units and mini-splits. Assuming you compare ACs of the same capacity, mini-splits have a higher efficiency than window ACs, and this also means they consume a lower wattage.
Air conditioners use a metric called the Energy Efficiency Ratio (EER), which is a ratio of BTU/h provided and watts consumed. For example, a 12,000 BTU/h air conditioner using 1,200W has an EER of 10. However, the EER only describes efficiency under a specific testing condition: 80°F indoor temperature and 95°F outdoor temperature. When you use a window AC or mini-split in a home, outdoor temperatures are constantly changing and the EER is not always accurate.
Two efficiency metrics are used to describe energy efficiency over a wider range of outdoor temperatures. These metrics are more accurate than the EER since they reflect real-world conditions:
- Window ACs use the Combined Energy Efficiency Ratio (CEER).
- Mini-split ACs use the Seasonal Energy Efficiency Ratio (SEER).
As of 2023, US federal standards require at least 12.0 CEER efficiency for window ACs between 8,000 and 14,000 BTU/h, and at least 15.0 SEER efficiency for split systems smaller than 65,000 BTU/h. The Department of Energy website has the complete list of minimum efficiency requirements for HVAC equipment.
Using these efficiency values, you can estimate the typical consumption of both window ACs and mini-splits. You can simply divide the cooling capacity in BTU/h and the rated efficiency (CEER or SEER) to estimate wattage. The following table provides an example of some common air conditioner capacities, between 9,000 and 24,000 BTU/h.
|
AC Capacity |
Window AC CEER Efficiency |
Window AC Wattage |
Mini-Split AC SEER Efficiency |
Mini-Split AC Wattage |
|
9,000 BTU/h |
12.0 |
750W |
15.0 |
600W |
|
12,000 BTU/h |
12.0 |
1,000W |
15.0 |
800W |
|
18,000 BTU/h |
11.8 |
1,526W |
15.0 |
1,200W |
|
24,000 BTU/h |
10.3 |
2,330W |
15.0 |
1,600W |
If you purchase a window AC with a higher CEER or a mini-split with a higher SEER, their power consumption is even lower. You can now find window ACs with up to 15 CEER and mini-splits with over 30 SEER.
What Size Generator Do I Need for a Window AC?
To power a window AC, you need a generator capable of providing its maximum wattage without being overloaded. However, you also need to consider battery capacity, to cover energy consumption over time. Solar generators have a rated power output (watts) and energy storage capacity (watt-hours).
Once you have verified that the window AC power input is lower than the generator power output, you can estimate how long the unit will run with a given battery capacity.
- Divide the battery capacity (watt-hours) by window AC power input (watts), and this will give you the battery duration in hours.
- For example, a battery capable of storing 1,500 watt-hours will run a window AC using 600W for 5 hours.
- A window AC consuming 1,000W will deplete the battery in 5 hours, and an even larger unit consuming 1,500W will deplete the battery in only 1 hour.
Best Solar Generator for a Window AC
Growatt INFINITY 1300
Boasting a LiFePO4 battery, the Growatt INFINITY 1300 LiFePO4 Portable Power Station can last for up to 10 years with 3,000+ cycles. It also has a power output of 1,800W and an energy storage capacity of 1,382Wh. Thanks to its high power output, the Growatt INFINITY 1300 can power household electricals, power tools, and even large appliances without breaking a sweat.
The table below highlights how long you can run common-size air conditioners with the Growatt INFINITY 1300 at full charge (1,382Wh):
|
Air Conditioner Capacity |
Wattage |
INFINITY 1300 Charge Duration |
|
6,000 BTU/h |
496W |
2.37 hours |
|
9,000 BTU/h |
750W |
1.57 hours |
|
12,000 BTU/h |
1,000W |
1.17 hours |
|
18,000 BTU/h |
1,526W |
0.77 hours |
Growatt INFINITY 1500
The Growatt INFINITY 1500 Portable Power Station has a power output of 2,000W and an energy storage capacity of 1,512Wh. Thanks to its high power output, the Growatt INFINITY 1500 is capable of powering small and medium-sized air conditioners.
The following table summarizes how long you can run air conditioners of common sizes, using the Growatt INFINITY 1500 at full charge (1,512Wh):
|
Air Conditioner Capacity |
Wattage |
INFINITY 1500 Charge Duration |
|
6,000 BTU/h |
496W |
2.59 hours |
|
9,000 BTU/h |
750W |
1.71 hours |
|
12,000 BTU/h |
1,000W |
1.29 hours |
|
18,000 BTU/h |
1,526W |
0.84 hours |
If you purchase an air conditioner with a higher efficiency rating, it can run for a longer time with 1,512Wh of charge. ENERGY STAR Certified air conditioners are a great option since they have been successfully tested for efficiency under stringent requirements, in approved laboratories that are independent of vendors and manufacturers.
FAQ
Will a 2000 watt generator run an air conditioner?
Yes, as long as the maximum power consumption of the air conditioner is below 2,000W. If the consumption exceeds 2,000W at any time, even briefly, the generator will be overloaded and its circuit breaker will trip. This will disconnect the air conditioner from the power supply.
Can a 1000 watt generator run a window air conditioner?
Yes, a 1000-watt generator can run the window air conditioner, as long as the window AC operates under 1000W, this type of window AC is usually a small to medium model.
How many watts does a window AC use?
This will depend on the cooling capacity of the window AC (BTU/h) and the rated efficiency (CEER). By dividing both values, you can estimate the average wattage consumed by the unit. For example, a 12,000 BTU/h window AC with 12 CEER efficiency will use 1,000 watts on average.
You also need to check the rated wattage on the air conditioner nameplate. The wattage value calculated by dividing cooling capacity (BTU/h) and efficiency (CEER) is the average power consumption. The wattage value on the air conditioner nameplate is the power consumption at maximum cooling capacity. Your generator must be sized for the maximum power consumption, not the average consumption.
