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How to Install a Window Air Conditioner Hero Image

How to Install a Window Air Conditioner

Learn just how easy it is to install a Window AC Unit with no prior experience.
Window air conditioner in a living room

Getting Started

As summer temperatures begin to rise, finding a way to beat the heat is essential. Installing a window air conditioner is an efficient, easy way to make sure you're comfortable in your own home. Keep reading to learn how to do it.
Your AC should come with a set of instructions that may have steps specific to that model. This guide offers detailed instructions that apply to all window air conditioners, but it's still important to check the manufacturer's instructions. If you don't have your air conditioner yet, take a look at our Air Conditioner Sizing and Buying Guide for help finding the right model for your space.

Install a Window Air Conditioner in 6 Easy Steps

Step 1: Pick a Window

Most window AC units are designed for single and double-hung windows. These are the most common types of windows in residential buildings. They feature two window panes, top and bottom, both of which are held in place with window sashes. Opening the window is as easy as sliding up the lower window sash. Double-hung windows also allow you to open the window by lowering the upper sash.
Use a casement window air conditioner if your windows open with a crank or slide open. The process for installing standard window units and casement ACs is nearly identical. However, it's more common for casement ACs to require a support bracket.
There are a few things to consider when deciding where to install your air conditioning unit. First, make sure your window is structurally sound. Air conditioners are heavy. If the window isn't secure, the AC could potentially fall and break, or worse, hurt someone.
To lighten the load on your AC, choose a window that doesn't get a lot of sun. The heat from the sun will force your AC to work much harder than it would in a shaded area. And while shady windows are ideal, air conditioners require adequate airflow to function efficiently. So make sure the window you choose will provide the window unit with 20" of clearance both inside and out.
Window AC graphic showing recommended distance for air flow
It's also important to choose a window that's near an electrical outlet that can handle the load. Air conditioner cords are usually six feet long and require a grounded outlet. Ideally, the AC should be plugged directly into the outlet. If you need to use an extension cord, only use those that are rated for appliances. And don't forget to make sure your AC won't overload the circuit. If the outlet you intend to use shares a circuit with other power-hungry appliances, consider a different outlet for the AC or the other devices.
Lastly, measure your window. Open the window fully and measure both the vertical and horizontal dimensions. Compare your measurements with those of the air conditioner you've purchased or any you plan to purchase. It's much better to find out your AC won't fit the window before you're lifting it into place.

Step 2: Prepare the Window and the Surrounding Area

Start by clearing the area of any tripping hazards. When you're done, wash the window, inside and out. If you plan to leave the air conditioner in place for the whole summer you may not have another chance for a while. While you're at it, clean the windowsill and frame as well.
Next, remove or raise the screen and/or the storm window. Window air conditioners need to hang over both sides of the windowsill. With the screen out of the way, find the horizontal center of the window and mark it with a pencil. Centering your AC distributes its weight along the sturdiest portions of the window frame and ensures the tightest seal.

Step 3: Prepare the Air Conditioner

If you have a new AC unit, start by removing it from the box. It's often easiest to open the box's top flaps, turn the box onto the open side, and then slide the box up and off the AC. This process is much easier with a helper.
Whenever you handle an AC, be careful where you place your hands. Some of the edges can be very sharp. The combination of sharp edges and a heavy air conditioner can easily cut your hands. Work gloves are a good way to keep them safe.
With the AC out of the box, attach the accordion side panels. Doing so is usually as easy as sliding them into place. However, some models will require screws to hold the panels in place. Refer to the manufacturer's instructions for details about your specific model.

Step 4: Install Mounting Brackets (Optional)

Most air conditioners will securely sit in your window without the need for brackets. However, brackets help protect the window from potential damage by providing a more stable footing and distributing the weight of the AC over a wider area. Models weighing 100 lbs or more often need these brackets for adequate support. Additionally, some buildings and even whole cities require them. New York City is one such example.
Because only the heaviest air conditioners require mounting brackets, you'll likely need to purchase them separately if you plan to use them. The brackets are fairly simple and some can be installed without tools. These typically secure themselves with extendable beams to create a sturdy hold on the window.
More traditional brackets must be screwed into place. To install these, refer to the manufacturer's instructions. The instruction will probably ask you to secure the bracket with two or more screws in your window sill.
It's useful to start by drilling a small pilot first. Doing so helps prevent wood and vinyl sills from splitting and makes it much easier to secure the screws. Make sure the width of your bit is slightly smaller than the width of your screw. To prevent the bit from drilling too deep, attach a bit of masking tape to it at your desired depth. The tape won't stop the drill from burrowing deeper, but you can use it as a guide to know when to stop.
Window air conditioner on the side of a blue house

Step 5: Lift the Air Conditioner into Place with a Helper

Carefully lift and place the AC unit in the window. If you're using mounting brackets, the AC should snap into place. Otherwise, just rest it on the windowsill. Pay attention to the pencil mark you made earlier and use it to center the AC.
Next, lower the bottom window sash onto the air conditioner to hold it in place. Most window ACs come with L-shaped brackets to secure the position of the lower windows sash. Typically, the brackets use two screws, one that attaches to the lower sash, one to the upper. Drilling pilot holes for these screws will make it easier to fasten them in place.
Window air conditioner locking bracket graphic
If you don't have L-brackets, you should be able to find them at any hardware or home improvement store. You can also secure the position of the lower window sash by wedging a piece of wood between its top edge and the top of the window frame. These spacers should be cut precisely to size and be sturdy enough to prevent you from opening the window while they're in place. A piece of wood with a width and depth of 2" should be sufficient.
Once securely in place, most air conditioners tilt ever so slightly to allow condensation to drain outside. This tilt is usually less than half an inch, but you should check the manufacturer's instructions for details about your specific model.

Step 6: Expand the Accordion Side Panels

Stretch the side panels to the edges of the window. To keep these panels in place, most ACs come with a set of small screws. Drill your pilot holes and secure the panels with the screws. Most air conditioners also come with foam weather stripping to seal any gaps you may have. Cut the weather strips to size and insert them between the upper and lower sash. If you notice any other gaps, perhaps between the AC and the windowpane, fill these with foam weather strips, too.
Window air conditioner with a couch in front

Step 7: Plug It In and Turn It On

In the first step of this guide, we made sure there was an appropriate outlet nearby. All that's left is to insert the power cord and enjoy the cool air.
If you still have questions about how to install an air conditioner or choosing the right model for your space, please reach out to us at 800-860-3577. Our AC experts can help you find the perfect window air conditioner, central air unit, mini split system, and more.