What Size Generator to Run 2 – 5 Ton AC Unit

You’ll need a generator between 7.5 kW and 20kW to run a 2-5 ton AC unit. Specific size generators with the power needed for AC units of these sizes are included below. The best generators to run AC units are listed below, and you can pick one for your home if you are planning a purchase.

In most cases, an air conditioner large enough to cool a home or business is the unit that will require more power than any other electrical appliance. So, a generator that will supply the power needed to efficiently start and run the AC is the very minimum size you will want to consider.

What Size Generator to Run Central Air Conditioners 2 – 5 Tons

This Generator for AC Size Chart shows the minimum power required for 2-5 ton central air conditioners. Generator size for the smallest residential central ACs, 1.5 tons, is shown too.

what size generator to run 2 – 5 ton ac unit

AC Unit Size (Ton)Generator Size (kw)
1.5 ton6kW
2 ton8kW
2.5 ton10kW
3 ton12kW
3.5 ton14kW
4 ton15kW
5 ton18kW

Rheem is one of the largest manufacturers of central air conditioners. The company’s numbers support the generator size for 2-5 ton ACs, as you can see in this manual for one of Rheem’s most popular ACs.


Top Generators for 3-5 Ton Central Air Conditioners

The minimum size generator we recommend is one that will power a 3-ton AC. That will give you enough for a 2 or 3 ton unit with some power to spare for other essential electric use such as lights or a refrigerator.

How big of generator to run ACs from 3-5 tons? We’ve got recommendations.

DuroMax XP12000EH Generator Gas or Propane Generator

Best Generator for 3 Ton AC

The DuroMax XP12000EH Generator Gas or Propane generator is the top choice for quality and dependability. It runs on propane or gasoline for versatile convenience.

  • Dimensions: 30 x 29 x 26 inches
  • Power Source: Dual Fuel
  • Voltage: 240 Volts
  • Wattage: 12000 watts

Champion Power Equipment 100111 15,000/12,000-Watt Portable Generator

You can’t go wrong with the Generac recommended for a 5 ton unit. But it’s a little expensive, and you can find something more affordable that is a suitable generator for 4 ton AC units.

The Champion Power Equipment 100111 is a cost-effective alternative with enough juice for 4 tons of AC.

  • Dimensions: ‎33.9 x 31.1 x 33.1 inches
  • Power Source: ‎Gasoline-Powered
  • Pattern‎: Generator
  • Wattage: 12000 watts

Generac 5735 GP17500E Gas Powered Portable Generator

Generac is a superior brand of generator. The Generac 5735 GP17500E has all the juice needed to run a 5 ton AC with no problem.

  • Dimensions: 48.5 x 31 x 39.5 inches
  • Power Source: gas-powered
  • Voltage: 120 Volts
  • Wattage: 17500 watts

Typical Generator Sizes

Generators with enough juice to run a large air conditioner are usually found with power outputs of between 7kW and 20 kW, with most in the 13-18kW range.

Because most people want to be able to run more than just their air conditioner during a power outage, the following chart lists what might be considered how big of a generator to run that would supply supplemental power to the entire home.

Size of ACMinimum Power for Whole House
2 ton12kW
3 ton15kW
4 ton20kW
5 ton22kW

How AC Units are Sized

Most people are familiar with the smaller, room-size AC units that fit in a window or sit on the floor in their home. Most have a cooling capacity of between 5,000 and 18,000 BTU. The largest of these are capable of cooling up to 1,000 square feet of living space if it is fairly open, but will not efficiently cool separate rooms.

Large air conditioners or heat pumps (which can both cool and heat) that are used for a whole house or small business start in size where the smaller units leave off. But they are normally rated in Tons rather than BTU. Since 1 ton is equal to 12,000 btu, an 18,000 btu unit is rated at 1.5 tons. A 24,000 btu unit is 2 tons, and so on up to 60,000 btu, which is 5 tons. Units between 2 and 5 tons are the most commonly found sizes for homes and small businesses.

Electrical Power is Needed

All AC units are powered by electricity. In a normal situation, this electricity comes from the grid to which the home or business is connected – the local utility company. During a power outage, a supplemental generator is about the only device that can produce the power needed to run the AC, as well as other electrical items.

Electrical power is measured in Watts. The electricity needed for a typical light bulb is between 60 and 100 watts. A large unit such as an air conditioner requires thousands of watts. One thousand watts is 1 kilowatt (1kW). When we know the kW requirements of our AC unit, we will know what the minimum size generator is needed to provide power for it.

Portable vs Whole House Generators

While the total power needed for a house or small business can be met by using a portable generator, a better option is to have a whole house generator installed and wired directly to your electrical panel.

Using a large electrical generator will eliminate the need for someone to be present to start the portable and connect it to the main breaker panel when power goes down. Many whole house generators are designed to start and automatically switch over in less than a minute after the main power is off.

Since whole house generators are often fueled by propane or natural gas, there is also no need to keep cans of gasoline on hand or to make sure the generator doesn’t stop because it ran out of fuel.

Summing it Up

As you can see, the electrical power needed for a 2 to 5 ton air conditioner is quite a lot. This is the main reason most people with whole house AC units experience a jump in their utility bill during the hot months of the year. But manufacturers of generators – both portable and installed – have managed to keep up with the increasing size of air conditioners so we can still run them when the local power goes out.


Where should I begin looking for a generator to power my AC unit?

We make recommendations above on units that can be bought on Amazon. They are top-rated generators for 3, 4 and 5 ton AC systems.

Locally, all of the “big box” stores carry both portable and whole house generators. Most of them will also provide a list of contractors that can install them if you need that. There are also local HVAC companies that can give you their advice, sell you a generator, and install it for you if that is what you want.

What about the noise – can I have a generator where I live?

Every generator makes noise, and some make more than others. Some municipalities and housing areas have restrictions on the amount of noise they will allow. Be sure to check your local regulations and your homeowner’s association (HOA) if applicable before making a purchase.

What is the best generator for 3 ton AC?

You’ll need at least 11kW, but generators usually don’t come in that size. To run the AC with extra power for essentials, consider a 14kW generator.

What is the best generator for 4 ton AC?

At minimum, you’ll want a 15kW generator, but a 17kW unit will give you assurance it will power the central air conditioner.

What is the best generator for 5 ton AC?

A 20kW generator will run a 5 ton AC. If you want more power for other appliances, lights, the refrigerator, or other electrical devices, choose a generator of 22-24kW.

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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