How Big of a Generator Do I Need to Run a Central Air Conditioner

Central air conditioners typically rely on electricity to run. However, one may ask how big of a generator do I need to run a central air conditioner?. So, if you want to use your central air conditioning system during a power outage, you’ll first need a generator that is large enough for the task. To find out how big of a generator you need, start by identifying the size of your central air conditioner.

When it comes to air conditioning units, the size of a unit does not refer to its physical size but its cooling power. And the size of these units is measured in tons. The standard range of a residential central air conditioning unit is 1.5 to 5 tons for homes with an average size of 600 to 3,300 sq feet. 1-ton is equivalent to 12,000 BTUs (Britsh Thermal Units) per hour. This blog post will determine what size generator is ideal for your central air conditioner.

What is The Size of My Central Air Conditioner Unit?


Central Air ConditionerUndersized or oversized central air conditioner units are a bad idea. An under-size AC unit will not cool your house adequately during summer. Additionally, it will have to run non-stop to provide a cooling effect to your home, and this will increase your electricity cost and increase its wear and tear rate. 


On the other hand, an oversized AC unit will quickly cool the house within a short running cycle. This may over humidify your home, leading to mildew and mold problems. So how do you identify the size of your central air conditioner unit?

Look Our for The Label

It is to identify the capacity of your central air conditioner unit. Most AC unit manufacturers give detailed information about the unit, including its size on its label. In most cases, you will find the size of your AC unit written after the unit’s model number.

How to Determine How Big of a Generator I Need to Run a Central AC Unit

The main grid can go off anytime, whether it is during the winter or summer. You will require a reliable generator to power your central AC unit during such times. However, not every generator can power a central air conditioner unit. There are different generator sizes for powering other electrical loads, including AC units. 


Central air conditioner units come in different sizes. Here are easy ways of determining the right generator size for your central air:


Look at the specification sheet for power on your AC unit

The manufacturer can recommend the wattage requirements of the model. These specifications can be in watts, making it easy to identify the appropriate generator size to run the unit. 

Look out for EER ratings on the specification sheet

This approach requires you also to check the AC unit’s size in BTUs. Proceed by dividing the BTUs by the EER rating to get the wattage requirements for the unit. For instance, if the AC unit capacity is 60000 BTUs (5 ton) and the EER ratings of the unit are 10: 60000 BTUs/10 EER = 6000 watts (wattage requirements). 

Look out for current (in Amps) and voltage (Volts/V) ratings of the AC unit on the specifications sheet.

You can get the wattage requirements of your AC model by multiplying the current by the voltage. For instance, if the AC model is rated 25 Amps and 240V, its wattage demands are 25Amps * 240V = 6000 watts.


Therefore a 6000 watts generator is capable of powering a 5-ton air conditioner. However, you will need a 7500 watt generator to cater to the starting power. The size of a generator is the most suitable size for running a 5-ton air conditioner.


Determining the size of your central air conditioner unit is important to ensure that you buy the right generator. Make sure to consult your local AC dealer and read your unit’s specification sheet carefully so that you know its wattage requirements. Then get a slightly bigger generator than the wattage requirements of your AC unit.


Factors to Consider Before Buying a Generator for Your Central AC unit

When shopping for a generator, there are a few factors you need to take into consideration. Here are some of them:

Types of Generators

You need to identify whether you need a stationary or portable generator before shopping for one. Stationary generators are available in different sizes and are permanently installed, while portable generators can be moved from one place to another.

It would be best to determine whether you need a conventional or an inverter generator. Conventional generators produce power that is not clean and can damage sensitive appliances. On the other hand, inverter generators produce clean power that is suitable for running sensitive appliances. 

Types of Loads

Another important consideration when buying a generator is identifying the appliances you want to power with it. If you want to run a central AC unit, you need a generator with enough wattage to power it. You may want to consider other appliances such as freezers, pumps, washers, dryers, ovens, heaters, etc. 

Power Requirements

For the generator power to run your appliances efficiently, it must be equal to or greater than the wattage requirements of the appliances. You should not overload your generator as this can damage it and may lead to an electrical fire.

Warranties and Maintenance

It is important to buy a generator that comes with a warranty. A good warranty cover will save you your investment in the long run. Be sure to read the warranty conditions before you buy the generator.

In addition, generators require periodic maintenance to ensure they are running efficiently. Maintenance includes inspecting the generator’s engine, oil levels, pump pressure, among other things. It would be best to buy a generator that is easy to maintain and has a long service life.

By considering these factors and doing your homework, you can purchase the correct generator which will power your AC unit reliably for a long time.

Frequently Asked Questions

Can a whole house run an air conditioner?

Yes, a whole house generator can run an air conditioner. However, before you plug in your air conditioner to your entire house generator, it is recommended that you counter-check the wattage requirements of the AC unit. Ensure your AC unit’s wattage requirements are low than what the generator can produce.

What size of a generator can run a 3 ton AC unit?

A 3 ton (36000 BTUs) air conditioner unit rated 30-Amp requires at least a 14KW (14000 watts) generator. Anything below this wattage will struggle to power the AC unit.

How big of a generator do I need to run a 12000 BTU air conditioner?

A 12000 BTU AC unit with a rating of 8 EER will require a 1500 watts generator to run. At the same time, the exact size of an AC unit but with a 12 EER rating will need a 1000 watts generator. A higher EER rating means the AC unit has high energy efficient rate.

Will a 10000 watt generator run central air?

Yes, a 10000 watt generator can power a central air conditioner when you are off the grid. Even so, it’s always advisable that you check your central AC unit wattage requirements. You can plan to power other appliances like lights once you ascertain how much power your central AC unit requires per hour. 

What size of generator to run a 2.5-ton ac unit?

A 2.5-ton air conditioner unit is equivalent to 30000 BTUs per hour. You will use a 10KW (10000 watts) generator to run such an AC unit. Such a generator will not struggle to power your AC unit. 

Can a portable generator run my home’s HVAC?

How Big of a Generator Do I Need to Run a Central Air ConditionerA portable generator can run a home’s HVAC unit if it has the required wattage to do so. To ascertain this, you need to find the wattage requirements of your HVAC unit and compare it with the portable generator in question.

How much of my house can I run on a 7500 watt generator?

You can run a range of domestic appliances including, a coffee maker, microwave, dishwasher, and a toaster with a 7500 watt generator. In addition, a 7500 watt generator is suitable for running a central AC unit.

How big of a generator do I need for a 3000 sq ft house?

You need to find the wattage requirements of the appliances in the 3000 sq ft house. The total wattage requirements will determine the appropriate generator size for your house. Always go for a generator with extra wattage output than your total wattage demand.

Final word

There are different central air conditioner units with different wattage requirements. It is important to do your homework and find the specific wattage requirements of the unit you plan to buy. Once you have that information, it will be easier to choose the right generator. Remember, a generator that is too small for your AC unit will struggle to run it and may even damage the appliance. A generator that is too big for your AC unit will be a waste of resources. Always ensure that you have the right generator size for your central air conditioner unit.

About Steve Stuart

Steve Stuart is an electrical engineer who developed interest on generators during his school years. After school, he became a generator enthusiast. This is after encountering power supply problems at the area of residence where he lived. Power would be on and off and so food would go bad and the room heater would go off especially during winter. After trying the different generator brands for several years, Steve now provides information on the available brands and products in the market today. Based on his experience, he gives the do’s and the don’ts when it comes to generator use.

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