HomeBLOGAir ConditionersHow To Install A Window Air Conditioner In a Casement Window?

How To Install A Window Air Conditioner In a Casement Window?

Installing window air conditioning units in casement windows may seem daunting, but it’s not. Of course, it would help if you had the correct equipment, a little know-how, and time to complete the job. Most come with instructions on installation and steps to ensure a proper, safe facility.

Installing a window air conditioner requires you to have all the right tools and materials. First, you must determine the location for placement. That means it needs to be centered on the window sill for most people. You will also need to choose the width of your casement window opening to determine how long your extension cord will be.

This article will help you determine the unit’s right size to fit the existing opening of your casement windows and some tips for you to consider when installing your new window unit.

What is a Casement Window?

A casement window is a class of windows that opens by swinging outward on a hinge. This window is generally held open using a crank, lever, or cam handle. Because they are opened with a crank mechanism, casement windows can be opened quickly and to any desired width.

Casement windows are suitable for modern homes due to their practicality and versatility. They can be installed on top of other windows, and they let in light and air than different window styles. 

Casement windows have the following benefits:

  • They open wide, allowing you to take advantage of airflow with less effort than other types of windows.
  • Because they are opened using a crank, casement windows are easy to use. 
  • They are handy for people with limited mobility or strength, as they require less effort to operate than many other types of windows.
  • Casement windows make it easier to minimize drafts – close the window tightly against its frame when you want to seal it against the weather.

Materials You’ll Need

Let’s look at the materials and tools to install your new casement window.

Equipment and Tools

  • Screwdriver
  • Drywall T-square
  • Pencil/Marker
  • Tape Measure
  • Ladder
  • Cutter


  • Selected Casement window A/C unit
  • Wood boards with accurate length and depth
  • Medium-sized particleboard 
  • Heavy Duty Plywood piece 

Window Air Conditioner Installation In a Casement Window By Yourself

Casement window AC unit

As a do-it-yourselfer, you can save money by installing your window air conditioner in a casement window. Window A/C units can be heavy, and they must be installed securely to operate safely and efficiently.

With just some essential tools and instructions on installing an A/C unit into a casement window, you can get your living space cooled down quickly and efficiently.

Here’s everything you need to know about installing an air conditioner in your casement window.

Choose Location

First, you’ll want to choose where to install your window AC unit. It should be a room that needs cooling and doesn’t already have an AC unit in the wall or ceiling. Some parts of your home are better suited for window units than others. 

Find a spot in your window where it’s relatively easy to install the unit and get it out again. Some good places are living rooms, garages, or even bedrooms.

Make sure there aren’t any outlets in the way unless you plan on using an extension cord. You should also check that there’s adequate clearance around the unit to have enough room for airflow.

Choose Unit

Pick one that will fit appropriately in the selected space. Measure the area before making a selection, and keep measuring until you’re sure.

Choose a unit that is the appropriate size for your room and make sure it will fit inside your window. Next, move the team into position and check if it will do. You may need to eliminate the side panels on the unit or turn the unit sideways. 

If your window is old, you may want to replace the windows before installing a new air-conditioning unit. It can save you money over time, plus the added insulation will help keep the cold air in and restrain hot air from entering your home through cracks in old or damaged windows.

Build the support base

This can be done by using scrap wood, cinder blocks, or anything else that has enough weight and is stable enough for your needs, as long as it doesn’t block any vents on the side of your home.

Most units over 6,200 BTUs will require this step. The accessible way to do this is with 2x4s and plywood cut to the appropriate size. You can then place the base on top of your windowsill and drill it with 3-inch deck screws or lag bolts.

Rip a piece of plywood that is the equivalent of width and height as the opening. Place it on top of the windowsill. Slide the air conditioner into place on top of the plywood, and then secure it with screws into either side of your window frame.

Install the Support Base on the Windowsill

Measure the width of your window and cut two pieces of lumber to this length. These will be the base pieces or top and bottom.

Measure the height of your window and cut two pieces of lumber to this length. These will be the sides that are going to support the base pieces. The ends of these side pieces should be cut at 45-degree angles for a mitered joint with the top and bottom base pieces.

Use a level to make sure your base is level, then attach it to the windowsill using wood screws or nails. Next, you create a box inside the window frame that supports your air conditioner unit.

Determine the Center Point

Measure from each side of the windowsill to find its center point. Next, measure half the width of your unit, add 3 inches, and mark this point on each side piece. It will be where you mount your bracket hardware to attach your A/C unit to the window frame.

Position the A/C unit in the window, ensuring it rests on the support base you installed earlier. You’ll need to ensure that the top of the A/C unit is at least four inches above your windowsill before installing.

If you have a metal security screen in front of your window, remove it before sliding the air conditioner. Leave the plastic window guards in place.

Position the A/C Unit in the Window

Ensure that the front legs are placed down on the window sill and resting on its side, with the back panel pressed against your side of the window frame.

Open the window and establish the air conditioner into the opening. Again, you can have someone help you with this step. Rest the bottom of the air conditioner against the lower window sash, and lean the top of it against the upper strap.

Position the unit so that its back is about one inch from the front edge of the windowsill to allow for proper drainage, and make sure it’s centered in the window opening.

Make Sure the A/C Is in Proper Alignment

Once your unit is settled into place, you’ll want to ensure that it’s in proper alignment. You can open and close your window until the A/C is centered. The open part of the window should be sitting flush with both sides of the air conditioner unit for proper fit. 

If there are any gaps, move the A/C or use shims to correct its position.

You’ll need to ensure that your air conditioner is appropriately aligned on the sides. If it is misaligned, you may have difficulty getting it to fit correctly into place. To check for alignment, open both windows to perpendicular to each other and then close them again to work together as a standard window would.

Fill the Top Gap

Make sure the window is open at least halfway. Then measure the height of the opening and compare it to the specifications for your air conditioner model. If there is a difference, adjust your bracket accordingly.

Attach the support bracket on the window frame using a hammer and screwdriver. Place the unit inside the window, ensuring that its bottom edge is flush against the shelf and its sides are resting on its frame.

Hold it in place while you drill screws into each bracket through holes in the air conditioner’s sides. Use foam weatherstripping tape to fill gaps between the unit and wall so that no outside air can get in or out.

Create a Tight Seal

Set your A/C unit in place at an angle to fit into the window frame to create a tight seal. The bottom of the A/C unit should fit snugly into the bottom of the window frame, and the top should be positioned just above where you want it to end up. 

Press down on the top of the A/C unit to bring it down into the window frame and make sure that the sides fit tightly into their slots in the frame.

Make sure the foam weather stripping is in place. If not, add it to the bottom edge of your window frame. The unit should be sitting on the foam weather stripping to give an airtight seal.

People Also Ask

Can you install a portable air conditioner in a casement window?

portable air conditioner in a casement window

Yes, you can install a portable air conditioner in a casement window. 

Installing a portable air conditioner in a casement window is easier than sliding windows.

Since casements are designed to be opened like that, they will stay stable and prevent accidents while keeping your portable AC safe from any damage that might otherwise occur if you were to place it on the ground outside.

You’ll also want to ensure that your portable AC is correctly sealed using plywood or Plexiglas.

Can you use a window air conditioner in a casement window?

Yes, window air conditioners are designed to fit both casement and double-hung windows.

The frame has side panels on each side of the unit, and those panels can slide back and forth to adapt with the width of the frame, so it fits the window’s width. That makes them compatible with casement windows, which have a crank handle that allows you to open and close them.

Some models of air conditioners are available that feature a removable chassis for casement windows. It is designed for windows that do not open out.

Can a window air conditioner be installed in a wall sleeve?

Yes. Wall sleeve installation is usually less complicated than a window installation, and you can use your unit’s slide-out chassis to make the process easier.

Wall sleeves are designed to hold window air conditioners, and they can be easily installed in a wall or through an exterior wall.

Many window air conditioners can be installed in a slide-out chassis wall sleeve, designed to fit into a pre-built hole in the wall. This type of sleeve is typically an aftermarket product, so before purchasing a window air conditioner, make sure that it has a slide-out chassis.


Casement windows can be handy for letting in the air on hot days. However, their pivoting doorways require special care during installation, especially if a window air conditioner is being put behind them.

Nevertheless, with proper care, a well-planned installation process, and the right tools, installing a window air conditioner in a casement window is possible—and it may even be easier than you think.

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