Can a Generator Power an Air Conditioner? (We Find Out)

The worst thing that can happen during an extended loss of power is hot weather. Usually, the power seems to be out when it is the hottest day of the year, leading many to attempt to run their air conditioners on their generators.

Generally, you will need at least a 4,000-watt generator to run a small air conditioner window unit and at least a 6,000-watt generator to run a whole-house air conditioner. An air conditioner needs lots of power, so you typically cannot use your generator for anything else simultaneously.

Many things affect the overall power that your air conditioning and your generator will work together. Most of the time, the conditioner will immediately pull away all the power from the system, as it requires an immense amount of power to starting and stopping the whole time.

What Size Generator Will You Need to Run an Air Conditioner?

Generator SizeGenerator WattsWhat It Will Power
Minimum4,000A small air conditioner and a few lights
Recommended6,000A medium-sized air conditioner, fridge, and a few lights
Safest10,000Nearly any size air conditioner, TV, fridge, lights, and many other household items

Before we discuss powering an air conditioner on a generator, you must take a look at the size of your system. The first and most crucial part is your generator; if it is too small even to start the conditioner, it may as well be useless.

Many homeowners want to skimp out of the size of the generator, as they assume they will never use it. However, they regret this way of thinking once they need the generator and cannot run more than a few things around the house, usually having to settle for just lights and the fridge.

The Minimum Size

If you plan to power your house, parts of your kitchen, and an air conditioner, we always recommend getting a minimum generator size of 4,000 watts. These are considered mid-sized generators and will usually be on the larger side of portable machines.

On average, this generator will power only one normal air conditioner in your home while powering a few lights and your fridge. It is important to remember that you will need to start things up sequentially, starting with the refrigerator, the conditioners, and the lights.

The Recommended Size

When running several power-hungry things throughout your house, it is essential to remember that each one requires more power to start up than they would while running. A fridge or TV only draws its maximum power on start-up, where conditioners differ; they always draw almost full capacity.

We recommend that you have a generator capable of providing at least 6,000W of power when you will be running any air-conditioner in your home. This prevents the generator from being over-taxed as the system works to cool down your home without drawing away power from other appliances.  

The Safest Size

Suppose you want to have a generator that can power your entire house, keep everything cool or hot, keep the kitchen running, and have power for a cup of tea; your generator needs to be much larger. We would recommend having a generator capable of providing at least 10,000W of power for this.

It may seem extreme, but a generator of this size will easily and comfortably power the average household and have enough power left to handle spikes. Further, a generator of this size can support several air conditioners and still provide enough power for other appliances in the home.

Can You Use a Portable Generator to Power an Air Conditioner?

You can use a portable generator to power an air conditioner, but they will need to supply a minimum power of 4000W. The average air conditioner for a small room uses around 3500W of power when starting up, with the power usage decreasing as the home cools.

While your generator will comfortably and fully power your air conditioner, it is essential to note that it will be running at its maximum output. Making the generator use a lot more fuel to power your air conditioning system, making it extremely fuel inefficient.

The increased fuel use on the generator is why people usually choose not to run their air conditioning when the power is out. Further, it’s important to note that a portable air conditioner may not use as much power but will constantly be running to have the same effect.

What Size Generator Will You Need to Run Common Sized Air Conditioners?

Air Conditioner Size (BTU)Watts Needed to Run Air ConditionerRecommended Generator Size
5,0005003,000 Watts
12,0001,2004,000 Watts
20,0002,0006,000 Watts
30,000+3,00010,000 Watts

Many times, the people that have generators that cannot power their air conditioning have not considered how large their systems are. An air-conditioner capable of cooling the entire house will naturally use a significantly larger amount of power than just a small one in the window.

We always recommend that people think about what size generators and air conditioners they will have in their homes when creating a system. If you have only small air conditioners in your home, you will run them on emergency power, but they may be ineffective in the long run.

5,000 BTU Air Conditioner

A 5,000 BTU air conditioner is one of the smallest air conditioners you can find, usually fitted directly to a window or a portable conditioner. These are great for cooling rooms up to about 200 square feet.

These conditioners only use around 500W of power when in use, which means you should be able to run them with ease alongside other appliances if you have a 3000W generator. However, it’s essential to note that this air conditioner will not be very useful in large rooms or homes.

12,000 BTU Air Conditioner

We consider the 12,000 BTU air conditioner size to be the average size that you can find in most homes as they are pretty effective at cooling down most rooms. To power this sized air conditioner, you will need a minimum generator of at least 4000W without running too many other appliances.

People constantly make a mistake when calculating how strong a generator they need. Air conditioners are not the only power-hungry appliance in your home, and you will need to calculate the total power consumption of your home.

20,000 BTU Air Conditioner

We skip past a few other air conditioning units to focus on 20,000 BTU units because this is usually where whole-house systems start. These units can use anything from 2000W or more to power on and cool down your home all at once, making them quite power-hungry.

We recommend having a generator that can provide at least more than 6000W of power when you have such a large air conditioning system. This will ensure that you can cool the home with ease and also that you can power other appliances without stressing about spikes.

30,000+ BTU Air Conditioner

It may seem odd if you already have a strong air conditioning system that people have and use 30,000 BTU systems. However, these usually consist of several connected air conditioners and automatically cool down the home or building when needed.

We always recommend having a large, permanent generator capable of providing 10,000W when you have such large systems. The deactivation of the conditioners and the use of other large appliances causes spikes in the total amount of power used throughout the home.

Why Do You Need Stronger Generators to Run an Air Conditioner?

Typically an appliance that is cooling something down or normally running would spike once it has started when you turn the motor on. This is how the fridge in your house works, with the motor needing a large amount of power to start turning, using less once turning.

Air conditioners are not entirely like this because the fan and the motor push the coolant through, turning on and off as needed. This means that it will constantly and randomly need to use the max amount of power that it can draw to keep the room at the perfect temperature.

Usually, this is why you will find that your generator is dying more often on days that the temperatures are colder. As the air conditioner stays on when it is sweltering, however, it shuts on-and-off when the room is already close to the right temperature.

What Is the Best Way to Run an Air Conditioner Off a Generator?

Now that you know what size generator you will need, we need to look at your home. There are a few extra steps to take to cool your house thoroughly. An air conditioner can often not be run while on a generator because it is being used wrong for the system.

We always recommend that people take these steps when the power is out and cannot handle the heat anymore. These steps will ensure that you do not overtax your generator and get the best performance from your air conditioning.

Run Only as Necessary

A common thing we have seen people do is running a generator to cool a room down to around 20oC when it is only around 25 oC outside of the house. They prefer to have the windows closed and have the air conditioner running to cool the inside down to a comfortable level.

We recommend that people rethink this way of cooling down their homes because it is much more effective to use the air-conditioner only once the temperatures become unbearable. This will save a lot of power overall and help keep sickness away as air-conditioners are not air filters.

Only Run One at a Time

The most vital advice you can follow with an air conditioner is to run it only where you do need it. People waste a lot of power by running air conditioners, even when nobody is in the room for several hours.

We recommend having all air conditioners turned off when running on a generator and preferably having everyone working in the same room. This allows for peak efficiency as the air conditioner in that room can comfortably cool it without others competing for power.

Don’t Constantly Switch On and Off

We have tried to explain this behavior a lot over the years, but we have met several people that turn their air conditioners on and off several times an hour. This wastes a lot of power, but it is incredibly wasteful and damaging when running on a generator.

The air conditioner needs to either be switched on or off, allowing it to do its work or having natural air flowing through your home. We cannot stress enough how much power you waste with the conditioner turning on and off again to try and stick to the whims of people.

Adjust Temperatures

If it is very hot outside, you need to be aware that having the air-conditioning trying to cool the office down to below 20 oC will use much more power. Adjusting the system to cool down to around 25 oC will be a lot more efficient overall and allow the generator to run more comfortably.

If it is colder outside, but you still feel hot, you need to consider allowing more natural air into the room you are in, as running an air conditioner to cool a room already around 20 oC is a waste. Usually, you will not be turning the system off after a few minutes anyway as it cools the room down too much.

Close Windows and Doors

Another thing that we often see people do when an air conditioner is being run is open doors or windows. This directly negates the effect of the system and will cause it to use a lot more power as it tries to cool down a much larger area constantly filled with hot air.

If you feel the need to have the windows and doors open while your air conditioning is running, you may want to move to a location where it is not running. We have seen many offices waste millions of dollars in power costs because one or two people open windows as soon as the air conditioning starts.

What Kind of Generator Do You Need for Central Air Conditioning?

You will need a much larger generator to power the system for central air conditioning, usually around 6000W or more. These conditioning systems have several valves, motors, and fans that are part of them that helps to control the airflow through the home.

These are also the strongest air conditioners because they are built to cool down large areas. We always recommend that you have a good generator that takes this into account when you buy one, as it can be a pain to cool a home that has these because of their insulation.

However, many people buy separate generators that only run the HVAC system, which many prefer. If you do this, you can use a much smaller generator to power the system without stress about the effect of other appliances on the machine.

How Do You Calculate What Size Generator You Will Need for Your Air Conditioner?

When you buy your air conditioner and your generator, you will need to calculate how they will work together. We have found several things that you will need to measure to properly ensure that you can cool the home even when there is no power for miles.

Many people have wondered why their generator that should power and efficiently work while powering their air conditioner randomly fails. Usually, a few select unexpected power drawing appliances around the house cause massive headaches during an outage.


Your appliances can use a shocking amount of power, especially when you have several active at all times. The fridge, the sound system, the PC, the washing machine, and the geyser are all things that will put a massive strain on your generator, causing it to shut down when you need it.

We always suggest measuring how much power you will need at the minimum when selecting or searching for a generator. Knowing how much power you need to run the house can be quite revealing to most people and means that you know where you may be wasting power.


Surprisingly, many people assume that they can have the generator placed in some corner close to their homes. Only to be fined when inspectors notice that you have installed the machine completely wrong, which you could have avoided by doing a bit of research.

A generator capable of easily power one or more air conditioners will usually be quite large, meaning that you will have to get the right space for it. If you don’t have the right or enough space for the generator, you may have to consider using a smaller one that will fit.

Air Conditioning

Once you have everything measured in your home, you need to see how the air conditioning will work. You must ensure the generator will be able to power it, and most of the time, you will already have the air conditioning installed in your home, cooling it.

We recommend that you consider this when choosing your generator and ensure that it can power the system and has enough overhead to support everything. Many people think about everything in the house, except the air conditioning, which we need to power.

Overall Usage

We mention this because many people consider everything in the home and then forget about total power usage. Most countries with regular power problems have these problems during the winter, whereas you will not need air conditioning in the summer.

Most of the time, you can calculate what appliances your generator will need to power by considering when you will use it. If you intend to use your generator during storms and hot weather, you need to consider that you’ll use the air conditioners then, while you’ll need heaters in colder months.

How Do You Calculate How Much Power an Air Conditioner Will Use?

Calculating just how much power an air conditioner will use at its peak power can be extremely difficult. Fortunately, there is an accepted standard for these units that is not always super accurate but does allow you to do quick calculations as to how much power they need.

Usually, you can measure how much power it will use by just removing one zero from the total BTU that the air conditioner is. This means that a 5000 BTU air conditioner will use around 500W of power at peak when it is in regular operation, with the unit rarely going above this.

However, air conditioners require a lot of power, sometimes even more than their direct rating. A 5000 BTU air conditioner placed in a large space or one with open windows can peak at using 600W of power to try and cool everything.


If purchased and correctly maintained, your generator can and will comfortably power your air conditioning throughout your house. It is important to remember that you will need to find a balance that allows the systems to work together to provide and use the appropriate power levels.

Whatever you do, please don’t think that the small handheld generator you bought for cheap can even help an air conditioner!


Hubert Miles

I've been conducting home inspections since 2002. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and an FHA 203k Consultant. I started to help people better understand whole-house and portable generators.

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