What Size Generator Do I Need to Run My AC?

Quick Answer: For central air conditioning, you typically need a large 5000–8000-watt portable generator or higher, depending on the cooling tonnage. A 2000–3000-watt portable generator can handle most window air conditioners except for larger 12000 BTU units. Portable ACs require 1000-1800 watts, so a 2000–3000-watt portable generator will work for them. Always check the exact wattage requirements of your specific AC unit. Choose a portable generator sized 20% above the running watts to allow for starting surge needs.


When your home loses power on a hot summer day, it doesn't take long for the temperatures to become unbearable. Your air conditioner requires electricity to run, so how do you keep your cool when the power goes out? The answer is a properly sized portable generator. Powering an AC unit requires quite a bit of wattage, so choosing the right portable generator is key. In this expanded blog post, we'll provide details on determining the ideal generator for your central air, window unit, or portable AC.

How Big of a Generator for Central Air Conditioners?

Central air conditioning systems place the highest electrical demands for cooling your home. These permanently installed split systems consist of an outdoor compressor and evaporator coil paired with indoor air handlers. The tonnage denotes the cooling capacity, with one ton equaling 12,000 BTUs. What size portable generator do you need for central air? Here are the detailed wattage recommendations:

  • 3-ton (36,000 BTU) central AC: 6,500-8,500 watts. A 7500-watt generator is ideal.
  • 4-ton (48,000 BTU) central AC: 8,000-10,500 watts. A 10,000-watt portable is recommended.
  • 5-ton (60,000 BTU) central AC: 9,500-12,000 watts. Opt for a 12,000-watt portable generator.

Always reference your owner's manual for the exact wattage ratings. Other factors like SEER efficiency, motor types, and fan speeds influence power draw. Central air conditioning start-up requires a momentary surge of 3-5 times the running watts. So, a 10,000-watt portable generator can struggle to start a large central AC despite having sufficient power once running. Consider a 15,000+ watt surge-rated portable to be safe.

Choose generators with inverter technology for stable, clean electricity. Voltage spikes can damage the control boards in air conditioning compressors. Maintain your generator properly with scheduled maintenance. Starting your central AC before the generator is fully powered on can overload the engine. Position the portable unit near your home's electrical panel to minimize voltage drop.

What Size of a Portable Generator for Window Air Conditioners?

Window air conditioners are a common way to cool a room. Mounted in a window opening, these self-contained units pull in outdoor air to evaporate refrigerant and cool your space. The British Thermal Unit (BTU) rating denotes the cooling power. Do you need a special generator for a window AC? Here are the typical portable generator wattages needed:

  • 5,000 BTU window AC – 900 watts. A 2000-watt portable generator is sufficient.
  • 6,000 BTU window AC – 1,100 watts. A 2000-watt portable generator is sufficient.
  • 8,000 BTU window AC – 1,200-1,500 watts. Use a 3000-watt portable generator.
  • 10,000 BTU window AC – 1,400-1,800 watts. A 3000-watt portable generator works well.
  • 12,000 BTU window AC – 1,600-2,000 watts. Use a 3000-4500 watt portable generator.

Always consult the user manual for your window AC unit's specific power requirements. Aim for a generator wattage capacity 20% above the listed running watts for optimal performance. Extension cord sizes and lengths impact voltage delivery, so position your generator close to the window AC and use heavy-duty cords. Turn off other appliances when starting the window AC to ease the initial starting load.

How Large of a Generator for Air Conditioners?

Need to cool just a single room? Portable air conditioners are easy to move and require less electricity than window units. Set them up, extend the exhaust hose vent, and they don't even need a window. Choosing the right generator for a portable AC depends on the BTU rating:

  • 8,000 BTU portable AC – 1,000 watts. A 2000-watt generator provides ample power.
  • 10,000 BTU portable AC – 1,200 watts. A 2000-watt generator provides ample power.
  • 12,000 BTU portable AC – 1,500 watts. Choose a 3000-watt portable generator.
  • 14,000 BTU portable AC – 1,800 watts. Select a 3000-3500-watt portable generator.

Check your owner's manual for the surge watts needed at start-up. Voltage drops can hinder performance, so use heavy-duty extension cords and keep the lengths short. Position the portable generator near the portable AC unit. Proper generator maintenance prevents power quality issues. With the right-sized generator, you can beat the heat anywhere power outages occur.

Approximately 1.5 hours of continuous operation

Stay Cool in a Power Outage

Don't let a power outage leave you sweating this summer. Determine the wattage needs of your specific air conditioning unit and choose an appropriately sized portable generator. With central air, window units, and portable ACs, the generator must provide steady, clean electricity free of voltage drops. Position generators close, use heavy-duty cords to minimize losses and take care of maintenance. Follow these guidelines so you can run your AC efficiently with a portable generator when the electricity goes out.

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