Skip to content
Home » How to install a window AC

How to install a window AC

Installing a window air conditioner is a practical and effective way to beat the heat in your home or office. This guide provides a step-by-step approach to ensure you can install your window AC unit safely and efficiently.

From preparing the windowsill and ensuring a tight seal with weather stripping, to securely placing and powering the unit, each step is designed to optimize your air conditioner’s performance and enhance your indoor comfort.

Whether you’re a seasoned DIY enthusiast or a first-timer, this article will equip you with the knowledge and confidence to tackle the installation process smoothly.

How to install a window AC

Installing a window air conditioner is a straightforward process that can significantly improve your comfort during warm months. Follow these essential steps to ensure a safe and efficient installation:

  1. Apply Blocking to the Windowsill:
    • Place a sturdy piece of wood on the windowsill to provide a stable base for the air conditioner, preventing it from tilting and ensuring even weight distribution.
  2. Apply Weather Stripping:
    • Seal the perimeter of the window frame with weather stripping to eliminate air leaks, enhancing the efficiency of your AC by keeping cool air in and hot air out.
  3. Install the Window AC:
    • Carefully place the AC unit on the prepared windowsill, lower the window sash to secure it, and use the manufacturer’s hardware to fasten the unit in place. Extend and secure the side panels to block outside air.
  4. Connect the Power:
    • Plug the air conditioner into an appropriate electrical outlet, ensuring it meets the unit’s power requirements and is properly grounded for safety.

By following these steps, you’ll be able to enjoy a cooler indoor environment while maximizing the performance and lifespan of your window air conditioner. Always refer to the manufacturer’s instructions for any specific requirements related to your particular AC model.

Apply blocking to the windowsill

You need to build a stable support structure that can hold the weight of your window AC. Some windowsills are wide enough to support a window AC without any modification. But most of the time its good to apply wooden blocking that can help support the weight of the unit.

Check that your wooden blocking is level using a bubble level and then tilt the support structure back slightly so that water will flow out of the window AC and into your garden.

You may want to also install a support bracket on the outside of your building if your exterior windowsill is not wide enough to support the part of the unit that will hang out the window.

Apply weatherstrip

The purpose of the weatherstrip is to create an airtight seal between your window AC unit and the outside air. You’ll need to apply weatherstrip to the top of your window AC and also to the top of your window’s lower sill. 

Weather stripping comes in various materials like foam, rubber, felt, or vinyl, and choosing the right one for your window type and climate is essential. For window AC installation, foam or rubber weather stripping is often recommended due to its durability and insulation properties.

  1. Measure and Cut: Begin by measuring the perimeter of your window where the air conditioner will sit. Measure each side of the window frame where the AC will contact it. Cut your weather stripping to these measurements, ensuring each piece fits each side of the window frame precisely.
  2. Clean the Surface: For the weather stripping to adhere properly, the window frame must be clean and dry. Use a mild soap and water solution to wipe down the area and allow it to dry completely. Any dirt or moisture can prevent the weather stripping from sticking securely.
  3. Apply the Weather Stripping: Start at the bottom of the window frame. Peel off the adhesive backing from your weather stripping and press it firmly into place along the bottom where the air conditioner will rest. Ensure it’s applied straight and without any gaps or overlaps.
  4. Continue Around the Frame: Repeat the process along the sides and top of the window frame, ensuring each piece of weather stripping butts up against the others without any gaps. The goal is to create a continuous seal that encircles the entire window opening.
  5. Check for Gaps: Once all the weather stripping is in place, inspect the perimeter for any missed spots or areas where the stripping isn’t flush against the frame. Press down on the weather stripping to ensure it’s firmly adhered to the window frame.
  6. Test the Seal: Close the window to test the effectiveness of the seal. You shouldn’t be able to feel any air coming through. If there are any leaks, adjust the weather stripping as necessary to eliminate them.

Properly applying weather stripping is a simple yet crucial step in preparing your window for an AC unit installation. It not only helps in cooling your space more efficiently but also contributes to energy savings by minimizing air leaks. With your weather stripping in place, you’re ready to proceed with installing the window AC unit securely.

Install the window AC

Before you begin, ensure the AC unit is the correct size for your window and that you have someone to assist you, as these units can be heavy and awkward to handle alone. Safety first: ensure the unit is unplugged during installation.

  1. Open the Window: Lift your window sash higher than it needs to be to fit the air conditioner into place. This gives you ample room to maneuver the unit without damaging the window frames or the AC.
  2. Position the AC Unit: Carefully place the air conditioner on the windowsill, sliding it into the open window. The bottom of the AC should rest securely on the blocking you’ve applied earlier, which provides a stable surface and helps distribute the weight of the unit. Most air conditioners have a lip or flange designed to sit over the inside edge of the window, preventing it from falling outward.
  3. Lower the Window Sash: Gently lower the window sash until it sits flush against the top of the air conditioner. This secures the unit in place and adds an extra layer of stability. Ensure the sash connects well with the unit without any gaps.
  4. Secure the Unit: Use the manufacturer-provided brackets, screws, and support brackets, if available, to secure the air conditioner to the window frame. This is crucial to ensure the unit doesn’t shift, vibrate excessively, or, in the worst case, fall out of the window.
  5. Adjust Side Panels: Extend the accordion panels from the sides of the air conditioner to the window frame, creating a tight seal that blocks hot air from entering and cool air from escaping. Secure these panels to the window sash and frame using screws if necessary, to fortify the seal and enhance the unit’s efficiency.
  6. Check for Stability: Before connecting the power, gently shake the unit to ensure it’s securely installed. There should be minimal movement, and the unit should feel firm in its position.

By following these steps, you ensure that your window AC is installed securely, optimizing its performance and efficiency. Remember, proper installation not only cools your space more effectively but also prevents potential damage to your window and the unit itself, ensuring longevity and reliable operation.

Connect the power

Once your window air conditioner is securely installed and the area is sealed with weather stripping, the final step is to connect the unit to a power source. This step is crucial for the safe and efficient operation of your air conditioner. Follow these guidelines to ensure a proper power connection.

  1. Check the Power Requirements: Before plugging in your air conditioner, verify its power requirements. Most window AC units require a standard 120-volt AC outlet, but larger models may need a dedicated 220-volt line. Ensure your outlet meets the voltage and amperage requirements specified by the manufacturer to prevent overloading the circuit.
  2. Inspect the Power Cord: Examine the air conditioner’s power cord for any signs of damage, such as fraying or cuts. A damaged cord can be a serious safety hazard, leading to shorts, electrical shocks, or even fires. If the cord is damaged, do not use the unit until the cord has been replaced by a qualified technician.
  3. Use a Grounded Outlet: For safety reasons, always plug your window air conditioner into a grounded 3-prong outlet. Avoid using extension cords or plug adapters that eliminate the ground pin, as this can increase the risk of electrical shock.
  4. Avoid Overloading Circuits: Air conditioners can draw a significant amount of power, especially upon startup. To prevent circuit overloads, do not plug other high-power devices into the same circuit as the air conditioner. If you’re unsure whether the circuit can handle the load, consult with an electrician.
  5. Plug In the Unit: Once you’ve confirmed that the outlet is suitable and the power cord is in good condition, carefully plug the air conditioner into the outlet. Ensure the plug is fully inserted and fits snugly, without any looseness.
  6. Test the Air Conditioner: Turn on the air conditioner using its power switch or remote control. Select your desired settings and allow the unit to run for a few minutes. Listen for any unusual sounds and monitor the unit for proper operation. It’s normal for the unit to emit a slight humming noise, but loud rattles or buzzing sounds may indicate a problem.
  7. Check the Air Flow: Ensure that cool air is flowing from the unit and that there are no obstructions blocking the front or back of the air conditioner. Proper airflow is essential for efficient cooling.

By carefully connecting your window air conditioner to a power source and ensuring all safety measures are in place, you can enjoy a cooler, more comfortable indoor environment. Regular maintenance, such as cleaning the filter and checking the cord and outlet, will help keep your air conditioner running smoothly throughout the season.