What Size Generator to Run an AC: Hourly Cost Breakdown

Determining what size generator to run an AC is crucial if you are planning a home renovation or for learning to maintain uninterrupted cooling during power outages or off-grid situations. In a typical household, air conditioners consume significant power, which makes it essential to choose a generator that meets the unit’s wattage needs.

While traditional fuel-powered generators have been in circulation for decades, solar-powered generators have emerged as a sustainable alternative as they provide a cleaner, quieter, and more reliable solution for running an AC unit. If you live in an area that faces frequent power outages, then you can check out solar-powered generators from Jackery, as they can effectively support various AC sizes without relying on gasoline or diesel.

Key Takeaways

• The required generator size depends on the AC unit's running and surge wattage.
• Small ACs can run on 2,000–3,500W generators, while larger ACs need at least 5,000W generators.
• If you wonder what size generator to run a 3-ton AC, then note that it requires at least a 12,000–15,000W generator.
• Diesel and gasoline generators incur ongoing fuel costs, with a 1.5kW AC consuming about $0.59 per hour on a diesel generator. Solar generators eliminate fuel costs entirely while providing a long-term solution.
• Using inverter generators, smart thermostats, and solar generators can significantly reduce energy consumption and operating costs.

How Many Watts Does an AC Use?

The wattage of a window AC unit depends on its size, type, and efficiency rating, but common household air conditioning models consume 500W - 2000W. If you wonder what size generator will run your air conditioner, then it is crucial to determine how much power it consumes. Here is a general estimation of the power consumption for different AC models:

• Window AC (5000 - 12,000BTU): 500W - 1,500W
• Portable AC (8,000 - 14,000BTU): 800W - 2,000W
• Central AC (2-5 Ton): 3,000W - 6,000W

Since all of the air conditioners that are currently being sold in the market have different power demands at startup and during operation, you must account for both running and surge wattages before learning the size of the generator you would require to run an AC.

How Many Starting & Running Watts Does an AC Use?

When a household or a portable air conditioner is turned on, it requires a higher initial power draw, which is known as a starting wattage. Once the compressor gets stabilized, the AC unit runs at a lower, continuous running wattage. An AC’s starting and running wattage depends on multiple factors, including wattage, ambient temperature, insulation quality, cooling load, etc.

Below is a comparative table of power consumption for various AC models:

How Much Energy is Needed to Run an AC?

In order to estimate the energy needed to run an air conditioner, you will need to consider the daily and monthly power consumption. The most generic calculator follows this formula:

Energy Consumption (kWh) = (Running Watts x Hours Used) / 1,000

For instance, if you want to know what size generator to run a 13,500 BTU air conditioner is required, and you want to first calculate its energy, then you will need to understand that a 13,500 BTU air conditioner typically requires 1,200–1,500 running watts and 2,700–3,000 starting watts. So, we will assume that the running wattage here is 1,500W, and it runs for eight hours every day. In this case:

• Energy Consumption (kWh) = (1,500W x 8 hours) / 1,000 = 12kWh per day.
• Over a month (30 days), the consumption will be 360 kWh.

With this simple calculation, one can determine if their generator can sustain their cooling needs efficiently or not.

How to Prioritize Power Usage During an Outage?

If you need to use an air conditioner during power outages, you will need to learn how to prioritize energy consumption. Running an AC on backup power would require strategic planning that would avoid overloading the generator while maintaining a well-optimized energy usage. Here are some key factors and strategies that you can follow if you intend to use AC during power cuts:

• Run the AC at Optimal Hours: Even if you have five-star rated Air conditioners, you will need to understand that it will consume significant power. It is recommended that you can use ACs during peak heat hours while minimizing nighttime use that would help you extend the generator's runtime. 
• Choose an Energy-Efficient AC Unit: Most inverter air conditioners and ENERGY STAR-certified models consume significantly less power and operate more efficiently than conventional ACs. Even though they might cost a little more, they can run on lower-wattage generators, making them an ideal option for usage when facing power outages.
• Opt for a Solar Generator: Traditional fuel-based generators require a continuous fuel supply, which may not always be available. Solar-powered generators like Jackery Solar Generator 5000 Plus provide a sustainable and cost-effective solution. These portable solar generators harness sunlight to recharge and deliver uninterrupted cooling for long hours.

Types of Generators Suitable for AC

Selecting the right generator that runs an air conditioner is an important decision influenced by factors like efficiency, power output, operational noise, fuel type, etc. As one can understand from the above table about air conditioner running wattage, the size and type of AC unit dictate the necessary power requirements. At the same time, the intended use cases, like using it as an emergency backup or off-grid living or recreational purposes, also play a significant role in understanding what size generator to run an AC and which type of AC is best for you.

Portable vs. Standby Generators

Most portable generators are compact, mobile, and ideal for temporary power solutions. They run on gasoline, propane, or diesel and can provide power during short-term outages. However, they require manual startup and fuel management, which might be tricky for those who are looking for a simple mode of operation.

On the other hand, standby generators are permanently installed units that automatically start when a power outage is detected. They offer higher power output but come at a higher installation and maintenance cost. At the very same time, getting standby generators in an already-constructed house or an apartment is extremely costly.

Inverter vs. Conventional Generators

If you prefer stable power and cleaner energy, you can always go ahead with an inverter generator. Since these generators provide stable power with variable speed operations, you can use them to power different appliances, including air conditioners.

However, conventional generators run at a constant speed, which provides consistent power but consumes more fuel and even produces a lot of noise while operating.

Fuel Type Considerations

Another factor that you need to consider is the fuel type. Diesel generators offer efficiency and durability but have higher fuel costs. According to a report published by EIA in February 2025, diesel price in the US stands at $3.68 per gallon, which makes long-term operations expensive. At the same time, gasoline is readily available but is less efficient than diesel.

For a sustainable, cost-effective solution, solar-powered generators are an ideal alternative. These systems use solar panels to charge built-in batteries, which provides a renewable and maintenance-free power source. With no fuel costs and minimal environmental impact, solar generators are an ideal alternative for running an AC unit efficiently without the ongoing expense of diesel or gasoline.

What Size of Generator to Run an AC?

If you are also someone who keeps on asking what size generator to run a 13,500 BTU air conditioner, then you will first need to understand that AC has high power demands. An undersized generator may fail to power AC effectively, and at the same time, an oversized one can even lead to unnecessary fuel consumption and increased costs.

Here’s a detailed breakdown of the process that you need to follow in order to answer what size generator to run an AC:

Step 1: Find the Running Wattage

As mentioned above, the running wattage of an AC unit refers to the continuous power it needs to operate after startup. This value can be found in the product manual or energy label. For instance, a 1.5-ton AC unit (18,000 BTU) typically requires around 1,500W to 1,800W of running power.

Step 2: Determine the Surge Wattage

Due to its built-in compressor, air conditioners require extra power during startup. This startup power or surge wattage can often be two to three times their running wattage. Considering the same example as taken above, a 1.5-ton AC with a running wattage of 1,500W may need 4,500W to 5,400W at startup. When you finalize the generator for your AC, you will need to ensure that it is capable of handling this surge.

Step 3: Add a Safety Buffer

If you need to improve the overall efficiency of a generator, you will need to remember that it should never be operated at maximum capacity for extended periods. It is always advisable to add a 20% safety buffer to the total wattage requirement.

So, if you have a 1.5-ton AC that requires 1500W for running and 4500W-5400W at startup, then the ideal generator should be rated at 2000W or more. This way, it can ensure efficiency and improve the overall longevity.

Step 4: Account for Additional Load

If you are someone who aims to use other essential appliances alongside your AC, like refrigerators, lights, televisions, etc., then you need to account for every appliance’s respective wattage. For instance, if you are going to use a refrigerator (800W) and a television (200W) together with the 1500W AC, the total requirement would be around 3000W including the buffer.

Step 5: Convert to Generator Size

Generator sizes are usually listed in kilowatts (kW). In order to convert from watts to kilowatts, you will need to divide the wattage by 1,000. This way, if your AC setup requires 3000W, then the recommended generator size would be at least 3000 - 3500W.

How to Calculate Cost Per Hour Usage of AC?

Once you have understood what size generator to run an AC, you will also need to analyze the cost of using the AC. This way, you can better evaluate your needs and choose the right generator. The primary considerations will include the AC unit’s wattage, efficiency of the generator, current fuel prices, and the overall duration of operation.

Breaking Down the Cost Per Hour

The first step in order to understand the cost per hour is to understand the AC power consumption. For instance, if you have a 1,500W AC that consumes 1.5kW. Different generators have different fuel consumption rates. So, if the AC runs at 1.5kW on a 10kW diesel generator that is operating at 50% load, then:

1.5kW ÷ 5kW = 0.3 

Since most ½ load diesel generators (10kWh) consume 0.53 gal/hr, then the 1,500W AC will consume 0.16 gallons per hour. As per the February 2025 diesel charges in the United States, the fuel cost per hour would be:

0.16 x $3.68 = $0.59 per hour.

Here’s an estimated breakdown of the cost that you need to pay for generators when used on different power supplies:

*The on-grid cost is taken from EIA.

Cost of Using AC for Different Generators

• As per the above table, the diesel generator will cost you $0.59 per hour if you use it for 1,500W AC. For larger loads, the cost may range from $1.00 - $2.00 per hour.
• If you go ahead with solar-powered generators, the cost of using a 1,500W AC would be $0, which eliminates the ongoing fuel expenses.

Best Jackery Solar Generators for AC

Jackery is a manufacturer of reliable solar generators for AC. Additionally, Jackery also manufactures a line of portable power stations and solar panels that provide consistent and reliable electricity to power different household and outdoor appliances, including ACs.

If you are tired of paying the humongous cost of diesel usage and planning to move to a more affordable and convenient power station, then you can check out Jackery Solar Generators and Jackery SolarSaga Solar Panels. These portable and compact solar generators for AC let you power your appliances and can also be used during camping or RV living.

Jackery Solar Generator 5000 Plus

The Jackery Solar Generator 5000 Plus is a high-capacity solar-powered generator designed to run energy-intensive appliances, including air conditioners. With a large battery capacity and a high peak surge capacity, this solar generator is powerful enough to support high-wattage appliances, including a 2-ton central AC. With Jackery Solar Generator 5000 Plus, you can even run a few household appliances alongside a mid-sized air conditioner, making it an ideal backup solution for your home and outdoors.

Appliance Running Hour

• 5,000 BTU Window AC (500W) = 7.7H
• 12,000 BTU Window AC (1,200W) = 3.4H
• 10,000 BTU Portable AC (1,000W) = 4.0H
• 14,000 BTU Portable AC (1,500W) = 2.7H
• 2 Ton Central AC (3,000W) = 1.4H
• 3 Ton Central AC (3,500W) = 1.2H
  

Customer Review

“Product works great and it was easy to install and integrated into my home.” -- Brian K.

Jackery Solar Generator 2000 Plus

The Jackery Solar Generator 2000 Plus is yet another powerful solar generator that can easily handle small to medium-sized air conditioners. If you are looking for an affordable, reliable, and convenient solar generator that you can carry outdoors, you can always rely on Jackery Solar Generator 2000 Plus. Along with Jackery SolarSaga Solar Panels, these generators offer a sustainable alternative for keeping air conditioners operational without reliance on diesel.

Appliance Running Hour

• 5,000 BTU Window AC (500W) = 3.3H
• 12,000 BTU Window AC (1,200W) = 1.4H
• 10,000 BTU Portable AC (1,000W) = 1.6H
• 14,000 BTU Portable AC (1,500W) = 1.1H

Customer Review

“Very easy-to-understand instructions. It was plugged in and charging within just minutes, literally. I am happy to have this for safety and security.” -- JSY.

FAQs on What Size Generator to Run an AC

How big of a generator do I need to run my AC?

The generator size required to run an air conditioner depends on the unit’s power consumption, including running and surge wattage. A small 5,000 BTU window AC typically requires 500-700 watts, while a 3-ton (36,000 BTU) central AC may need 4,500-6,000 watts of running power.

Will a 7500-watt generator run my air conditioner?

Yes, a 7,500-watt generator is powerful enough to run most medium-sized air conditioners, such as a 2-ton (24,000 BTU) central AC, which typically consumes 3,500-4,500 watts with a startup surge of 10,000 watts.

What size generator is to run a 13,500 BTU air conditioner?

A 13,500 BTU air conditioner typically requires 1,200–1,500 running watts and 2,700–3,000 starting watts. A generator rated at least 3,000-3,500 watts is recommended to ensure a smooth startup and continuous operation.

What size generator is to run a 15,000 BTU air conditioner?

A 15,000 BTU air conditioner usually consumes 1,500–1,800 running watts, with a startup surge of 3,000–3,500 watts. To run this unit reliably, you will need a 3,500-4,000 watt generator.

What size generator is to run an 18,000 BTU air conditioner?

An 18,000 BTU air conditioner requires approximately 1,800–2,200 running watts and can demand 4,500–5,500 watts at startup. A 5,500-6,000 watt generator is recommended to handle both the initial surge and continuous operation.

Conclusion

Asking what size generator to run an AC is not only important if you are into home renovation, but is also a crucial point to discuss if you are tired of paying hefty amounts against your diesel cost or wish to reduce your reliance on the on-grid power supply. There are several generators that can run an AC, but if you want a reliable option, look no further than Jackery Solar Generators. These generators feature an ergonomic design, which makes it extremely easy for you to carry from one room to the other.