DIY Guide: How To Install A Sliding Window Air Conditioner

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Installing an air conditioner in a sliding window is a project many can do at home. What is a sliding window air conditioner? It is a special type of AC unit designed to fit into windows that slide open sideways, either left or right. Can I use a regular AC in a sliding window? No, standard window ACs, made for windows that open up and down (double-hung), usually won’t fit a sliding window. This guide will show you how to set up a sliding window air conditioner, often called a vertical window air conditioner, safely and correctly.

Picking the Right AC Unit

Before you start, you need to find the right air conditioner. This is key for good cooling and easy setup.

Determining the Right Cooling Power (BTUs)

Cooling power is measured in BTUs (British Thermal Units). Too small an AC won’t cool enough. Too large an AC will cycle on and off too often, wasting power and not removing humidity well.

Here’s a simple guide for room size and BTU needs:

Room Size (Square Feet)BTU Needed
150-2505,000-6,000
250-3507,000-8,000
350-4509,000-10,000
450-55011,000-12,000
550-70013,000-14,000
  • Tips for BTU Choice:
    • If your room gets a lot of sun, add 10% to the BTU number.
    • If many people are often in the room, add 600 BTUs per person.
    • If the AC is for a kitchen, add 4,000 BTUs.

Measuring Your Window

This step is very important for a good fit. Sliding window ACs are often tall and narrow. They fit into the vertical space of your window.

  • Measure the opening:
    • Measure the exact height of the open part of your sliding window. Do this from the sill (bottom) to the top of the open pane.
    • Measure the width of the open part. This is usually the width of one sliding pane.
  • Check AC dimensions: Look at the product specs for the AC unit. It will list the height and width of the unit itself. It will also list the range of window heights it can fit into. This range accounts for the sliding window AC side panel kit that comes with the unit.
  • Clearance: Make sure there’s enough space around the window outside. The AC needs air to flow freely.

What to Look for in a Sliding Window AC

When buying, consider these points:

  • Type: Make sure it’s for sliding windows. These are often called “vertical window ACs” or “casement window ACs” because they are tall and narrow.
  • Energy Efficiency: Look for an Energy Star label. This means it uses less power.
  • Features:
    • Remote control for easy use.
    • Sleep mode for quiet, efficient night cooling.
    • Programmable timer to save energy.
    • Different fan speeds.
    • Washable filter for easy cleaning.

Tools and Materials You Need

Gathering everything before you start makes the job smoother and safer.

Tools for Installation

  • Phillips screwdriver: For screws on the AC unit or brackets.
  • Drill: With drill bits for pilot holes if needed for brackets.
  • Level: To make sure the AC is straight. A small torpedo level works well.
  • Tape measure: For accurate window measurements.
  • Utility knife or scissors: To cut weatherstripping.
  • Safety glasses: To protect your eyes.
  • Work gloves: To protect your hands.
  • Pencil: To mark spots for drilling.

Materials for a Secure Setup

  • The sliding window air conditioner unit: With its instruction manual and all parts.
  • Foam or rubber weatherstripping: To seal gaps.
  • Duct tape or foil tape: For extra sealing.
  • Wooden or metal shims (optional): To adjust level if needed.
  • Window AC support bracket (strongly recommended): For safety and stability.
  • Window sash lock or security bar: To stop the window from being opened from outside.
  • Small pieces of wood (for security): To put in the window track.

Getting Ready for Install

Good prep work prevents problems later.

Safety First

  • Read the manual: Every AC unit is a bit different. Read the instructions that come with your specific model.
  • Lift with care: AC units are heavy. Get help if you need it. Lift with your legs, not your back.
  • Power off: Make sure the outlet you’ll use is ready and can handle the AC’s power. Do not plug the unit in until it is fully installed.
  • Clear the area: Remove anything around the window that might get in the way.

Cleaning the Window Area

Dust and dirt can make sealing harder.

  • Wipe down the window sill, frame, and tracks.
  • Remove any old weatherstripping or leftover sticky residue.

Pre-Assembly of the AC Unit

Some AC units need a bit of assembly before going into the window.

  • Attach side panels: Most sliding window ACs come with a sliding window AC side panel kit. These are often accordion-style panels that extend to fill the window’s width. Follow the manual to attach them to the main unit. They usually slide into grooves or snap into place.
  • Drain plug: Check if there’s a drain plug. Make sure it’s in place if the unit needs it.

The Step-by-Step Installation

Now, let’s put that air conditioner in! This part covers the core steps of vertical window air conditioner setup.

Step 1: Install the Window AC Support Bracket

This is a very important step for safety. A window AC support bracket helps hold the weight of the unit and keeps it from falling out.

  1. Place the bracket: Hold the support bracket against the outside of your window sill. The bracket often has adjustable legs that go against the wall below the window.
  2. Adjust height: Adjust the bracket so it sits just below where the AC unit will rest in the window. The goal is for the AC to be slightly tilted outwards (about 1/4 inch per foot) so water can drain properly. Use a level to check.
  3. Mark and drill: Mark the spots for screws on the window sill or frame. Drill small pilot holes.
  4. Secure the bracket: Screw the bracket firmly into place. Make sure it’s very stable. Some brackets may need screws into the house siding below the window.

Step 2: Placing the AC Unit in the Window

This is where you lift the AC into its spot. Get help if the unit is heavy.

  1. Open the window: Slide your window open wide enough for the AC unit to fit.
  2. Lift and position: Carefully lift the AC unit. Place its bottom edge onto the window sill. The unit should sit against the vertical frame of the fixed part of your sliding window.
  3. Align: Push the AC unit firmly against the fixed window pane. Make sure the unit is sitting flat on the sill and that its back is resting on the support bracket.
  4. Close the sliding pane: Slowly slide the movable window pane against the side of the AC unit. It should fit snugly against the unit’s frame.

Step 3: Extending and Securing Side Panels

The sliding window AC side panel kit fills the gap between the AC unit and the window frame.

  1. Extend the panels: Pull out the accordion-style side panels until they reach the side of your window frame.
  2. Secure the panels: Most units have holes in the side panels or their frames. Use screws provided to fasten these panels to the window frame. This helps seal the unit and keeps it firm. Do not overtighten screws.
  3. Check for gaps: Look for any large gaps around the panels or where they meet the window frame.

Step 4: Leveling the Unit

Even with a support bracket, you need to check the level.

  1. Use a level: Place your level on top of the AC unit.
  2. Adjust the tilt: The unit should be slightly angled down towards the outside. This tilt helps water drain away from your home. If it’s not tilted, you can use small shims (thin pieces of wood or plastic) under the outdoor side of the unit or adjust the support bracket. Aim for about a 1/4-inch drop for every foot of AC depth.

Step 5: Sealing the Unit for Energy Efficiency

Proper sealing is critical. It stops cool air from escaping and hot air, bugs, and rain from coming in. This covers sealing sliding window air conditioner and weatherstripping window AC installation.

  1. Foam strips: Your AC unit likely came with foam strips. Cut these to size and press them into any gaps around the main unit and the side panels. Pay close attention to:
    • Where the movable window pane meets the AC unit.
    • Where the side panels meet the window frame.
    • Any gaps at the top or bottom of the unit.
  2. Weatherstripping: Use foam or rubber weatherstripping window AC installation tape to seal any remaining cracks.
    • Apply it along the edges where the sliding window pane meets the fixed window pane.
    • Apply it where the side panels meet the window frame.
    • Also, seal the gap where the top of the movable window pane meets the top of the window frame.
  3. Duct or foil tape: For extra sealing, especially on the outside, use duct tape or foil tape over seams and gaps. This is very good for drafts.
  4. Fill the track: Fill any open parts of the window track with foam or weatherstripping.

Step 6: Sliding Window AC Security Measures

Once your AC is in, you must secure your window. This stops the window from being opened from the outside.

  1. Window sash lock: Install a window sash lock or a thumb screw lock. These devices screw into the window frame and the movable pane, stopping the pane from sliding open.
  2. Security bar: Place a security bar in the track of the window. This is a metal or wooden rod cut to fit the exact gap. It physically blocks the window from sliding open.
  3. Wood in the track: For an extra simple security measure, cut a piece of wood. Place it snugly in the window track between the edge of the sliding pane and the window frame. This makes it impossible for someone to open the window more.
  4. Screws: For long-term security, you can put a small screw through the top track of the sliding window, above the movable pane. This makes the window fixed in place with the AC. Be careful not to damage the window.

Special Considerations for Different Window Types

While this guide focuses on sliding windows, it’s good to know about other window AC setups.

Distinguishing Casement Window AC Installation

You might hear “casement window AC installation” or “mounting casement AC unit.” It’s important to know the difference.

  • Sliding Windows: These have sashes that slide horizontally (sideways) or vertically (up and down, like double-hung). Our guide is for the horizontal sliding type, where the AC unit typically stands tall and narrow.
  • Casement Windows: These windows open outwards or inwards, usually with a crank. A typical sliding window AC unit will not fit a casement window without special adapters. There are specific tall, narrow AC units made for casement windows. These are often called “casement ACs” or “vertical ACs,” but their installation method is very different from the sliding window setup we covered. Mounting a casement AC unit involves fitting it into the opening created by the crank-out window, often with a different kind of mounting frame. If you have a casement window, make sure you buy an AC made for that type, and follow its specific instructions.

Reinforcing DIY Vertical Window AC Setup

The process described in this guide is essentially a DIY vertical window AC setup. Because sliding windows open sideways, the air conditioner unit must be tall and narrow to fit the vertical space. All the steps for installing a sliding window AC, from placing the unit to sealing and securing it, apply directly to a vertical setup. This type of installation is common in many modern homes with sliding window designs.

Testing and Final Checks

After all the hard work, it’s time to test your new AC.

Powering On and Testing

  1. Plug it in: Plug the AC unit into a proper electrical outlet. Make sure the circuit can handle the load. Avoid extension cords unless absolutely necessary and rated for AC use.
  2. Turn it on: Set the AC to a low temperature and high fan speed.
  3. Check for cool air: Feel for cool air coming from the front of the unit.
  4. Listen for strange noises: The unit should hum smoothly. Any grinding or loud rattling might mean a problem.
  5. Check for drainage: After some time, check outside for water dripping from the drain hole. This means it’s removing humidity well.

Final Checks for Efficiency and Safety

  • Check all seals: Go around the entire unit again. Feel for any drafts or air leaks. If you feel air moving, add more weatherstripping or tape.
  • Verify security: Try to push or pull the window from the outside (if safe to do so). Make sure it’s completely secure and cannot be opened.
  • Clean the filter: Most AC units come with a cleanable filter. Make a habit of checking and cleaning it every few weeks. A clean filter helps the AC run better and saves energy.
  • Read the remote: If your unit has a remote, learn how to use all its features.

Frequently Asked Questions (FAQ)

Can I use a regular AC made for up-and-down windows in my sliding window?

No, a regular AC unit for double-hung windows (that slide up and down) is usually wider than it is tall. It won’t fit well or safely in a sliding window that opens sideways, which is typically tall and narrow. You need a specific sliding window AC, also called a vertical window AC or casement window AC.

How do I keep my sliding window AC secure from theft?

To make your sliding window AC safe, use a window sash lock or a security bar. You can also place a strong piece of wood in the window track to block it from opening further. Some people also put screws through the window frame to keep the window from moving.

Why is sealing around the AC unit so important?

Sealing is very important for two main reasons. First, it stops cool air from leaving your room and warm air from getting in. This makes your AC work better and saves you money on power bills. Second, good sealing keeps out bugs, dust, rain, and noise. Use foam strips, weatherstripping, and tape for a tight seal. This is key for good sealing sliding window air conditioner results.

Do I really need a window AC support bracket?

Yes, using a window AC support bracket is highly recommended. It takes the heavy weight of the AC unit off your window frame and sill, making the installation much safer and more stable. It helps prevent the unit from falling out, which could cause damage or injury.

What if my sliding window is very wide?

Sliding window AC units come with a sliding window AC side panel kit. These panels extend to fill the extra width of your window. Make sure to choose an AC unit whose adjustable panels can cover the full width of your window opening. If your window is unusually wide, you might need extra insulation material to fill the remaining gaps after extending the panels.

Conclusion

Installing a sliding window air conditioner is a smart DIY project. It can bring cool comfort to your home without the cost of a full central AC system. By picking the right unit, gathering your tools, and following these steps carefully, you can enjoy a cooler home. Remember, safety, proper support (with a window AC support bracket), and good sealing are the most important parts of a successful setup. Enjoy your cool air!

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