How to Install Window AC in Horizontal Sliding Window

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Window air conditioners are not typically designed for double-hung windows, not sliding ones. Here, we present the step-by-step guide on installing your box-type window AC in a sliding window, which is helpful when you already have a window-type unit to install.

How to Install a Window Air Conditioner in a Sliding Window: A Step-by-step Guide

Step 1: Gather Your Materials

You will need plywood in this installation as this will fill in the gaps between the sliding window opening and the window frame. Go for thicker plywood, around 3/4 of an inch to an inch thick. This will provide enough insulation for your room to prevent the outdoor heat from passing through.

Step 2: Remove the Window Screen

Slide the frame to completely open one side of the sliding window. Dismantle any bug screen or dust screen from your window. You'll need to leave the window completely open to fit your window air conditioner.

Step 3: Separate the AC from its Housing

Carefully unscrew the housing of your unit from its internal components, and set the rest of the unit aside. Take the housing of your unit, and attach the metal brackets where the support brackets will attach to.

Step 4: Align the Housing, and Screw in the Brackets

Align the housing of your unit to the window frame, and mark the points where you will be drilling your air conditioner in a sliding window. This will help serve as a guide to install your AC unit. Install the steel support brackets outside your sliding window, tilting it slightly outward.

Step 5: Measure Your Plywood

Measure the wide gap between your air conditioner and your window frame. Take note of these measurements as you will need them to custom-cut your pieces of plywood. It is helpful to measure the width of the window so you can get the right thickness of plywood to create an air-tight seal.

Cut the plywood according to the size of the gap in your window. Mark the pilot holes, and thin out the plywood at these markings to drill in the screws later when you're installing your air conditioner in a sliding window.

Step 6: Add Foam Insulation

Add foam-type insulation on all four sides of the window pane, including one at the base of your air conditioning unit by the window sill. Insulation will keep the cool breeze of your air conditioner in, while keeping the warm outside air out.

Step 7: Piece it All Together

Place the plywood on the gap, and fill in any remaining gaps, or loose parts with some insulating foam. Screw in the air conditioner into the pilot holes, and secure the metal bar for the support brackets. Ensure everything is tightly secured before placing the internal components back into the housing.

Step 8: Place the Unit Back in its Housing

It is a good idea to use a vacuum cleaner or blower to remove any installation debris and sawdust from the housing of your air conditioner. This will keep your AC unit clean longer, and prevent any problems in the future. Carefully place the internal parts of the unit back into its housing. Secure your air conditioning unit by screwing the housing back into place.

Step 9: Plug in Your Unit

Finally, plug in your unit and check if your unit is working properly. If your unit is not working well, inspect your installation to see if there are any loose screws or misaligned parts, and adjust accordingly. For complicated AC problems, contact our technicians at Luce Aircon to diagnose your unit.

Step-by-Step Installation Guide Video

Need a visual for the installation guide? Check out this video for a step-by-step process, and follow the guide to install your air conditioner in a sliding window without any problems!


1. Do I need to separate the unit from the housing?

While separating the unit from its housing is not a required step, it is helpful in aligning the air conditioner to the window framing. The air conditioner housing is relatively lightweight compared to the entire unit, and it is easier to measure the pilot holes using just the housing. So while this step is not required, it is recommended.

2. Can I use other materials aside from plywood?

Yes, you can use other materials besides plywood, as long as it can fit within your window frame, and provide insulation from the heat outside. Plywood is preferred as it is a cost-effective and readily available solution, but it may not fit well into your home design aesthetics. You may use PVC boards, cork, or even fitted plexiglass panels instead.

3. Will my aircon dealer install my window air conditioner for me?

Many aircon dealers offer installation services at a cost, but may not necessarily install a window-type air conditioner in a sliding window. Before purchasing your window air conditioner, scout for dealers who can provide installation services for your room given the sliding windows.

4. Are there alternative air conditioners for homes with horizontal sliding windows?

Yes, there are plenty of options in portable, wall-mounted split types, and central air conditioners that work wonderfully in homes with horizontally sliding windows. Ask one of our technicians at Luce Aircon for recommendations on air conditioner brands and models that would suit your room size.

5. Can Luce Aircon install my AC unit for me?

Yes, our Luce Aircon technicians offer both purchasing and installation services, besides our cleaning and maintenance services. Contact us to inquire about our services, and we can discuss installation options for your standard air conditioner.

We're only a call away! Luce Aircon is your one-stop shop for all things AC - so give us a call, and we'll get to you immediately.

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