How Big of A Generator to Run a 5,000 – 15,000 Btu AC Unit

How Big of a Generator to Run a 5000 – 15000 BTU AC Unit

There’s a lot of faulty information online about how large a generator to start an AC – a window, RV or portable AC – and keep it running.

The correct answers to the question are found here.

As a bonus, the Pick HVAC generator experts have chosen the:

  • Best generator for 15000 btu air conditioner
  • Best generator for 13500 btu air conditioner
  • Best generator for 8000 btu air conditioner
  • Best generator for 5000 btu air conditioner

Buy one today – or use our recommendations to continue to research the question of how large a generator to start a unit of the size you have.

What Size Generator to Run 5,000 – 15,000 BTU Air Conditioner

Here’s the table.

The Generator Size in Watts takes into account the extra watts needed to start the window, portable, RV or other unit that isn’t a central air conditioner.

What Size Generator To Run 5,000 – 15,000 Btu Air Conditioner:

Air Conditioner Size (BTU)Generator Size (Watts)
5,000 btu1500 Watts
6,000 btu1500 Watts
8,000 btu1500 Watts
10,000 btu2000 Watts
12,000 btu2000 Watts
13,500 btu2800 – 3000 Watts
15,000 btu3500 Watts
18,000 btu4500 Watts
24,000 btu5000 Watts

Q: Will a 2000 watt generator run a 5000 – 8000 btu air conditioner?

A: Using the chart, you can see that a 2000 watt generator will power an AC up to 12,000 BTUs. So yes, a 2000 watt generator will run a 5000 – 8000 BTU air conditioner.

Q: How large a generator to start a 15000 BTU AC?

A: The chart shows that a 15000 BTU AC requires 3,500 watts to start. A good choice would be a 3,500 or 4,000 watt generator.

There are generator options below for ACs of many sizes including 15000 BTU.

Did you know that start watts and run watts are different, and we’ll explain that below.

For the AC sizes in the chart, here are start watts and run watts, if you’re interested.

  • 5,000 BTU – Start: 1100 watts / Run: 600 watts
  • 6,000 BTU – Start: 1200 watts / Run: 700 watts
  • 8,000 BTU – Start: 1350 watts / Run: 800 watts
  • 10,000 BTU – Start: 1500 watts / Run: 1000 watts
  • 12,000 BTU – Start: 2000 watts / Run: 1200 watts
  • 13,500 BTU – Start: 2800 watts / Run: 1800 watts
  • 15,000 BTU – Start: 3500 watts / Run: 2100 watts
  • 18,000 BTU – Start: 4500 watts / Run: 2350 watts
  • 24,000 BTU – Start: 5000 watts / Run: 2500 watts

Not all units of the same size use exactly the same power. The efficiency of the AC will affect the watts it uses. But these ratings cover most.

Q: Why are more watts needed to start an AC than to run it?

A: Because the power demand to get the compressor going is significantly higher than to keep it going.

It’s common physics – Newton’s Law of Motion. To paraphrase for our purposes, an object at rest wants to stay at rest, but once it’s going, it takes less power to keep it going than to start it going.

Central air conditioners use something called a start capacitor to give them the extra boost needed to start. Window, RV and portable units usually don’t have anything like that.

Best Generators to Run 5,000 to 15,000 Watt ACs

We’re often asked questions like – how large a generator to start a 5000 BTU (or 8K, 10K, 15K BTU, etc.) AC?

Well, here are answers to these questions. We’ve researched the best generators to power air conditioners for the RV and room air conditioners for your home, either window or portable.

Best Generator for 5,000 BTU Air Conditioner

WEN 56200i 2000-Watt Gas Powered Portable Inverter Generator

You’ll find this AC generator very handy for air conditioners and many other uses. It’s loaded with features to make your power outage less of a nuisance. And it is ideal for camping, RV use and more.

  • Run Watts: 1600
  • Peak Watts/Start Watts: 2000
  • Fuel: Gasoline
  • Start: Recoil pull
  • Features: 1-gallon fuel tank. Can be combined with a compatible generator for additional power. Runtime is up to 9.4 hours. 12V DC receptacle, 5V USB port. Two 120V receptacles. 51dB on low power. 2-year warranty.
  • Voltage: 120 volts

Best Generator for 8,000 BTU Air Conditioner

Westinghouse WH2200iXLT Super Quiet Portable Inverter Generator

This Westinghouse portable generator has plenty of power to get your window, portable or RV AC started and running, with a little bit left for other essentials.

This is a gasoline-powered pull recoil unit.

  • Run Watts: 1800
  • Peak Watts/Start Watts: 2200
  • Fuel: Gasoline
  • Start: Recoil pull
  • Features: 1.3-gallon gas tank for up to 13 hours of runtime. Can be combined with another of the same unit to boost maximum power. It is compatible with several other Westinghouse iGen generators. Run noise as low as 52dB.
  • Voltage: 120 volts

Best Generator for 13,500 BTU Air Conditioner

Hudson Motors 3300-Watt Super Quiet Portable Inverter Generator

Start and run a 13500 BTU AC with no problem with this highly rated generator from a reliable brand.

It is built with a dependable 4-stroke 145cc overhead valve (OHV) engine.

  • Run Watts: 2800
  • Peak Watts/Start Watts: 3300
  • Fuel: Gasoline
  • Start: Recoil pull
  • Features: 1-gallon tank with up to 4 hours of runtime. It includes a low-oil shutoff, energy-saving ECO mode, 2 120V/20-amp receptacles plus a 120V/30-amp outlet. Two 5V outlets are included. This Hudson Motors generator can be combined with another to maximize power.
  • Voltage: 120 volts

Best Generator for 15,000 BTU Air Conditioner

Champion Power Equipment 200914 4250-Watt Open Frame Inverter Generator

Champion Power Equipment is one of the top names in generators, and this is a good example of why these units are so reliable.

This best AC generator runs on gasoline or propane with maximum starting power of 4250 watts for either fuel.

Click on this generator to see your options including this unit, a gas-only unit with the same power and a lower cost and the same unit with remote start.

  • Run Watts: 3500 gasoline; 3150 propane
  • Peak Watts/Start Watts: 4250
  • Fuel: Gasoline
  • Start: Recoil pull
  • Features: Dual fuel. Up to 22 hours runtime on gasoline. Hook it up to a large propane tank for longer running times. The generator is equipped with 2 120V 20-amp receptacles, a 12V DC outlet and a dual USB adapter. It’s backed with a 3-year warranty.
  • Voltage: 120 volts


This section might clear up additional questions you have about the best AC generator for 500 to 1500 BTUs.

Will a 2000 watt generator run a 5000 – 8000 btu air conditioner?

Yes. A generator that size will start and power an AC up to 12,000 BTUs.

How many watt generator to run 15000 btu ac?

According to our Chart above, the minimum power to start a 15000 BTU AC is 3500 watts. It takes 2100 watts of run power.

The Champion Power Equipment generator recommended above is an ideal choice.

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

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