How to Install a Window AC Unit?

Carolina Evans
Carolina Evans
Research Writer
Holds a Master’s degree in Engineering and is keen on her own home’s climate. Sometimes we think that Carolina owns every single product she writes about – that’s ho read more
Reviewed By
Richard Powell
Richard Powell
Expert Consultant
For 8 years, Richard had been working as an HVAC specialist and AC unit installer since his student years. Now, he’s our main consultant on every technical aspect that may read more
Last updated: August 22, 2023 is reader-supported. We may earn a commission through products purchased using links on this page. Learn more about our process here

If you want to know how to install a window AC unit, then you’ve come to the right place. For those with a suitable window, it can be a great way to cool down the room during hot summer months. However, it’s vital that you take the right steps to get the perfect fit.

In this guide, we will go through all the preparation that you need to do before you put the AC in and complete instructions on how to install it. While it may seem like a big job, it’s quite simple to do, but you’ll probably need a spare pair of hands.

By the time you get to the end of this guide, you’re going to be confident in knowing how to properly install a window AC unit. Let’s get started!

Preparation steps

How to Install a Window AC Unit?

Preparation is key to knowing how to install an air conditioner in a window. Here, we will take a look at what you need to check first before we look at how to install a window air conditioner.

Check if you’re permitted to install a window unit

It’d be a huge waste of time and money if you decided to install an AC unit in your window only to find that it’s against regulations. For most homeowners, this isn’t usually going to be a problem, but it could be if you live in the likes of an apartment or complex.

It’s important to check with your management or homeowner’s association before you buy your new AC model.

Some don’t like them due to the safety risks of a poorly installed machine falling out of the window, whereas others don’t like the aesthetics.

Keep in mind the size of your room

There’s no point installing a small AC unit for a giant room as it’s just not going to have the right amount of power. It’s easy to work out the square footage of your room by simply multiplying the length times the width. When it comes to buying your AC, it should clearly state the maximum area of effectiveness, and you need to get one that matches your room.

Don’t forget about energy efficiency

Each AC unit should come with its own energy efficiency rating (EER), and this will range from 8 to 12. In this respect, the higher the number, the better. An energy-efficient unit is not only going to be better for the environment, but it’s also going to reduce your bills as AC units can consume a large amount of power.

Get the tools

You may think that you’d need a lot of tools to install a window AC unit. In fact, it’s going to be minimal. Here, we take a quick overview of what you need.

  • Screwdriver
  • Measuring tape
  • Scissors

The reason that’s all that you’re going to need is that the manufacturer will provide all the screws and brackets that you will need for a secure installation. Most window AC’s are fairly simple to fit.

Remove the AC unit from the box

You need to be careful when removing the AC as it’ll be quite heavy, and it can also have parts on it, which are quite sharp. As with any large package, you should inspect that you have all the right pieces. You don’t want to get halfway through installation only to find you can’t go any further and have to send it back or get new parts.

Open the window and measure it

You need to make the measurements of your windows before getting an AC unit. These types of AC’s are designed for double-hung windows where you’re going to be able to slide the bottom half straight up. Other types of windows aren’t going to be suitable.

If you’re wondering how to install an AC unit in a vertical window, then the same process applies. As long as you have that double-hung design where you can slide the window across, you’ll be fine.

You’ll also need to have a power outlet fairly close to the window. Extension cables aren’t designed for this level of power, and they should, therefore, be avoided.

You should also choose a window had doesn’t have anything blocking the air inside or outside.

Once you have the right window, then open it as wide as possible and measure the height and width. All models of AC will tell you in the specifications the minimum and maximum window size they can fit into.

Installation process

How to Install a Window AC Unit?

Here, we are going to look at the step-by-step guide on how to properly install a window air conditioner.

Attach side panels

It’s more or less certain that the AC unit isn’t going to be the exact same size as your window. The side panels are designed to block any airflow around the unit. The panels will just slide onto the unit and can then be secured by screws. You want to make sure all of the screws are connected to make it as airtight as possible.

There is no point in trying to pull out the side panels at this stage as it’ll only make installation more awkward. Slide them all the way in until you have the unit secured in the window.

Insert the air conditioner in the window

Firstly, grab a friend. AC units are usually light enough for one person to carry, but when it comes to getting it in the right position and holding it in place for screwing, it becomes very difficult. If you try and do it yourself, then you can well end up with a broken mess on the floor.

The next step is to simply pick it up and place it in the center on the window. It’s best to mark out the central point with a pencil beforehand. Most AC’s will have a slot in the unit that it will be able to rest on.

The bulk of weight will be sitting outside the window, which is another reason that it’s a good idea to have a helper with you. After this, you can then close the window as tightly as possible onto the AC unit. It should now sit on its own, but you want it to be more secure.

If you’re not wondering how to install a small window AC unit and intend to install something bigger and heavier, it will also come with a bracket for the outside of the window.

Rather than this being permanently attached to your home, the bracket is usually just a simple frame that is screwed into the bottom of the unit, which then rests some weight on the outer wall.

Secure everything up

There are just a few bits to clear up before you’re ready to go. The first part is checking the L-brackets that go on top of the opened window, and it will prevent the unit from sliding up once it’s screwed in.

Hopefully, your AC came with some padding to put on the sides of the open window to create an airtight seal. You then slide the panels across from the unit and into the padding. You’ll then be able to screw these panels into the window for a secure fit. After this step, you’re done!


Hopefully, by now, you’re confident in how to install a window AC unit. It transforms a room from a sweaty nightmare into a cool and comfortable environment. As you have seen here, it doesn’t require much expertise.

As mentioned, it’s important not to assume that you’ll be permitted to install an AC and also double-check that your window is compatible. Once you have the right space and tools, it’ll get it installed in no time at all.

While this is general advice, each manufacturer is different, and it’s always a good idea to check the instructions. After a little bit of hard work, you’ll be able to enjoy the benefits of a brand new AC unit.

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