Does a Window AC Unit Need a Dedicated Circuit?

A typical window AC unit will need its own dedicated circuit. While there are small units that do not require a dedicated circuit, these situations are less common. It is important to have a dedicated circuit so as to not cause an overload.

Window air conditioner units are often the most efficient and cost-effective tools to cool down a room in a home.

However, maintaining safe electrical practices and proper circuitry is the most important step in keeping a window air conditioner performing at its best. 

Most people in the U.S. these days have central heating and air in their homes, but there are quite a few folks that rely on window units to keep themselves cool on a hot day.

Read on to better understand exactly what factors establish whether your window air conditioner unit would need its own dedicated circuit. 

Related: Does A Window AC Pull Air From Outside?

does a window AC unit need a dedicated circuit

What Determines Whether a Window AC Needs a Dedicated Circuit?

While some smaller window air conditioner units might not require their own dedicated circuits, the factors below will help you determine whether your specific circumstances call for adding one. 

  • Voltage of the AC unit
  • Amperage of the AC unit
  • Size of the room
  • Any applicable building codes

Voltage Of The Window AC Unit

Any electrical load is generally measured in three ways: volts, amps, and watts. Each of these measures a different property of the circuit. We’ll start by talking about voltage.

There are two* different voltages available for appliances in a home: 120 volts and 240 volts. Most window air conditioner units are 120 volts, though some larger ones are 240 volts.

  • 120 volts: These units often require a dedicated circuit, but there are some exceptions, as discussed below.
  • 240 volts: These units will almost always require their own circuit, since any nearby circuit has a 99% chance of being 120 volts.

*Note: There are other low-voltage categories, but they don’t apply to this topic.

These values are nominal. 120 volts represents a voltage range from approximately 110 to 130 volts. Likewise, 240 volts signifies a range from about 220 to 250 volts.

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Keeping that in mind, let’s talk about the differences in a bit more detail.

The typical outlet in your house that you would plug a vacuum or toaster into is 120 volts. In fact, probably 90% or more of the circuitry of your house is 120 volts (the exceptions being bigger loads such as electric ranges, ovens, dryers, etc.).

This is the main reason window air conditioners are manufactured to be 120 volts. Being the same voltage as nearby outlets makes it easier for people to install a window AC, without the extra trouble and cost of having to add a new circuit.

However, it’s not quite that simple – as we’ll see in a moment when we discuss amperage.

It’s critical that your air conditioner voltage matches your circuit voltage. Otherwise, it simply will not work and will possibly ruin your unit.

In other words, if you have 120-volt unit, you must plug it into a 120-volt outlet on a 120-volt circuit.

In order to cool a larger space, you need a more powerful AC. And the bigger the AC, the more power it requires.

There are two ways to increase that power: raising the voltage or raising the amperage. We’ll deal with amperage in the next section.

The largest window air conditioners are 240 volts because you can get twice the cooling out of a 240-volt unit as you can out of a 120-volt unit (at the same amperage).

Sounds good, right? Well, the problem is that 240 volts is not your typical outlet voltage in a house. So, in order to use a 240-volt AC, you’ll need to run a new circuit for it.

Since that may not be practical for many homeowners, most ACs are built to run on 120 volts. So this naturally limits the size of the unit. However, since most window air conditioners are used for bedrooms, a smaller unit is usually adequate.

But if you need to cool a large family room or other space, you may have to get a larger unit and install a 240-volt circuit to power it.

Related: What’s The Best Way To Heat A Large Space?

Amperage Of The Window AC Unit

Even the smallest window air conditioners require a fair amount of power. Amperage is the primary measurement of this power.

Note: Most air conditioners are rated in watts. Use the following formula to find amps.

Watts = Volts x Amps

  • Your average 120-volt units range from 4 amps (5,000 BTUs*) to 12 amps (14,000 BTUs).
  • Typical 240-volt units can be anywhere from 7 amps (18,000 BTUs) to 12 amps (25,000 BTUs)

*Note: BTUs (British Thermal Units) are a measurement of heat and are simply used here as a means of comparison.

As you can see, for the same amperage, you can get a lot more work out of the 240-volt units.

But your window AC unit voltage must match your outlet and circuit voltage. This is why, if you’re looking to install a new unit, and you don’t want to run a new circuit, the first thing to do is check what amperage you have available on the existing circuit.

To determine amperage, you have to know what other electrical loads are on the circuit. A load is any device or appliance (including lights, fans, etc.) that are powered by the circuit.

Also, you must include any potential load that will utilize that circuit. Think about what devices might be plugged into that circuit’s outlets in the future (computer, TV, vacuum, etc.).

It’s a simple matter of adding up all of the existing and potential loads (in amps), and subtracting that number from the rated amps of the circuit. The rated circuit amps is determined by the circuit breaker. Use the equation above to convert watts to amps.

So, for example, if you have a 20-amp circuit, and a calculated existing/potential load of 12 amps, then you would have 8 amps of “space” left on the circuit. This means you could arguably add an 8-amp air conditioner to that circuit.

However, that approach is not a best practice, nor recommended.

It is always better to leave yourself some wiggle room on circuit space. You don’t want to get into a situation where your circuit is maxed out and constantly on the verge of tripping the breaker.

If you can at all muster the extra cost of installing a new circuit, do so. There is more than one advantage to this.

Not only do you have peace of mind that your circuit is fully adequate, but it opens up your options for air conditioner size. You can choose the AC you want, rather than settling for what your existing circuit will allow.

Before we leave this section, I want to mention something in case you’re planning to replace an old unit with a new one.

Even if a dedicated circuit was installed for a old unit, make sure it meets the voltage and amperage requirements for any replacement unit you wish to install. This will prevent having to replace the old circuit with an entirely new one.

Related: Why Are My Window AC Lights Flashing And Beeping?

3D House plan room sizes

Size of Room

A larger room will require the air conditioner to do more work and use more power, pumping cool air into the space. While the size of the room often refers to the square footage, it also applies to the height of the ceiling.

Rooms like bedrooms, living rooms, garages, and workshops are all great candidates for a window air conditioning unit. While these rooms vary in size, some of them are typically quite large.

Use a handy air conditioner BTU calculator to figure out the correct size unit for your room.

Related: How To Circulate Air Conditioning In An Apartment

Building Codes

It is important to always consider applicable codes when building and installing items in your home. Some regions have specific building codes that include requirements for window air conditioner units.

Take these into account when determining whether your window air conditioner unit will need its own dedicated circuit.

This is not only for safety, but also for resale integrity. An installation that does not meet code can be a red flag to a home inspector and possibly throw a monkey wrench into the selling process.

Read: How Cold Is The Air From An Air Conditioner?

Potential Consequences of Not Having a Dedicated Circuit 

You might be wondering, “What’s the worst that could happen if I don’t have a dedicated circuit for my window air conditioner unit?” Well, if a window air conditioner needs its own circuit and does not have one, it could lead to several negative results. 

Circuit Overload

First of all, a circuit is a loop through which electrical current flows to power an electric device. Every item that plugs into an outlet in your home requires a circuit to function.

A simple house circuit is made up of three main components:

  • Circuit breaker
  • Wire (conductors)
  • Load (appliance, light, etc.)

The main job of the breaker is to protect the wire from getting too hot, melting, and catching fire. The breaker restricts the amount of amperage allowed on the wire by tripping at a certain amp rating (e.g. 15 amps, 20 amps, etc.).

With a properly sized breaker, the wire will never be in danger of having more amperage pulled through it than it can handle.

The load determines how much amperage gets pulled through the wire. If you have a 9-amp air conditioner, then it will draw a maximum of 9 amps through the wire.

Now, let’s say you have a 10 amps worth of loads (lights, electronics, etc.) on a 15-amp circuit. Then you plug in a 9-amp air conditioner. That’s 19 amps total.

The AC will try to draw more amps than the breaker will allow. There are two possible outcomes to this:

  • Breaker trips: Ideally, the breaker trips as it is supposed to, protecting the wire.
  • Breaker fails: Sometimes, the breaker is bad and doesn’t trip when it should. This could easily lead to a fire.

You don’t want to rely on your breaker tripping every time your circuit overloads. That is tempting fate, for sure!

Read: Why Window AC Compressor Keeps Turning On And Off

Electrical Fires

As mentioned above, there is a serious risk of fire if a circuit is overloaded. Though it is rare for a breaker to “fail on”, it has been known to happen. So it’s best to not put it to the test unnecessarily.

If your breaker happens to be one of the unlucky ones, you could be in a dangerous situation. This is even more likely if the breaker has been tripped and reset many times due to the overload. Over time it will inevitably get weak and fail.

This goes for any appliance, not just a window air conditioner.

In fact, it is more common for these types of electrical house fires to occur in the winter when people are using heaters. But any load that is too large can be a danger.

It is always better to err on the side of caution when installing any appliances on an existing circuit, including window air conditioners. 

overloaded extension cord
Photo courtesy of 40/29 News

Extension Cord Overload

Some people try plugging their window air conditioner unit into an extension cord instead of installing a dedicated circuit. This is not a good idea, as many extension cords are not rated for use with window air conditioner units.

Overloaded extension cords are one of the leading causes of house electrical fires. They are not intended to be used on a permanent basis.

Unless the extension cord is large enough for the job, plugging an appliance into the cord could cause electric shock or start a fire. If you do use a cord temporarily, make sure it is of adequate gauge size.

Image courtesy of

Another downside to using extension cords is that they are notorious for being a tripping hazard. If a window air conditioner is set up in a bedroom, likely, a person will occasionally walk around the room in the dark.

It is always better to have a dedicated circuit than to use potentially dangerous or reckless shortcuts.

Read: How Much Does A Window AC Unit Increase Your Electric Bill?

Installing a Window AC with A Dedicated Circuit

Now that you know your window air conditioner unit will likely require its own dedicated circuit, you are probably ready to begin cooling your rooms.

Now it’s time to determine the feasibility of adding a circuit and installing the AC unit. In some situations, it is just not economically practical to install a new circuit to the location you would like to put the air conditioner.

Make sure you are able to afford the entire project before beginning. If you’re not doing it yourself, adding a new circuit can be a bit pricey – and an unexpected budget drain.

Also, be sure the window can hold an air conditioner unit. There are several types of windows, and your air conditioner unit will require a certain kind to fit and work properly. You don’t want to inadvertently damage your window by force-fitting anything.

The window you choose should not be in direct sunlight, if that can be helped, or else you will never get the full air conditioning benefits from the unit.

Here are a few quick tips on an installation, but be sure to follow the instructions for your particular unit.

Have Help on Hand

Window units are heavy. It usually takes more than one person to install an air conditioner unit into a window; otherwise, there is great potential for personal injury or damage to the window or the unit itself. 

Take Precise Measurements

Measure, measure, and measure again.

You will need to know the height and width of the opening of the window in which the air conditioner unit will sit. Be sure the unit you choose is small enough to fit easily into that opening.

window air conditioner in bedroom

Obtain Appropriate Accessories

Determine what accessories you will need and have them prepared. Mounting rails, side panels, weather stripping, and brackets are all available for certain window air conditioner units.

Depending on the size, weight, style, or brand of air conditioner unit you purchase, some or all of these items may be necessary for your setup.

L-brackets will most certainly come with your window air conditioner unit. These are crucial to ensure the window in which your unit sits will remain shut, and your unit will stay in place.

Also, accordion-style side panels will usually come with the unit to fill up the extra space on either side of the unit.

Related: Is It Worth Buying A Portable AC?


Any home appliance can be a challenge to install, but doing your homework ahead of time will greatly reduce any potential headaches along the way.

Window air conditioners can last for many years if installed properly and maintained. This starts with providing a dedicated circuit. 

If you’re skilled and handy enough, you can certainly install the circuit yourself, with the appropriate guidance and knowledge. However, most people will not feel comfortable doing so.

It may seem expensive or inconvenient to pay an electrician to install a dedicated circuit in your home. It is well worth the cost, however.

A professional installation will aid in the prevention of potential fire damage down the road. It is a cool price to pay for peace of mind.

Related: Why Is Air Conditioning So Expensive?