How to Install a Window Air Conditioner Unit

A window air conditioning unit is the perfect way to beat the summer heat without breaking the bank. Window AC units are cheaper than through-wall air conditioners and easier to install, making them an excellent choice for homeowners on a tight budget. While most window AC units can be installed quickly without much hassle, there are a few things you need to know before you get started that will make your life much easier.

Below you’ll find a detailed step-by-step guide for covering how to install a window AC unit, followed by some general tips and frequently asked questions.

Find a local contractor near you if you’re having trouble installing a window air conditioning unit.

Guide for How to Install a Window A/C Unit

Below, we’ll include instructions on how to install a window AC unit in 10 simple steps.

1. Gather Necessary Tools and Materials

Before you head down to your local hardware store, make sure you have the necessary tools available. You’ll need:

• Screwdriver
• Level
• Tape Measure
• Drill (depending on the AC you purchase)

It’s a good idea to gather the tools you’ll need beforehand, so you can purchase them when you pick up your AC if you need to. You’ll also need some of the tools to measure your window to determine what kind of air conditioner you need.

2. Assess and Measure Your Window

Purchasing a window AC unit without assessing and measuring your window first is a great way to have to make multiple trips to the store. Most window air conditioners fit a range of window sizes, but not all units will fit every window.

Measure the width and height of your window opening at its narrowest point, taking special care to notice any protrusions that might prevent a window AC from sitting in the frame.

While you’re measuring, pay attention to the state of your window frame. Check for signs of decay or rot and use your level to make sure your windows don’t show any signs of warping or sagging. Warped window frames can be a sign of moisture problems but can also be a clue that you have serious foundation issues that require immediate attention.

3. Assemble AC Unit

Once you have your new AC home, unbox it and follow the instructions for assembly. Some window air conditioners don’t require any assembly, while others take some time to put together.

Make sure to check for damaged parts before you assemble the AC to avoid the hassle of taking it apart if you need to return it. Pay particular attention to the metal fins on the back of the unit. If any fins are bent or wrinkled, you should probably exchange the unit since the fins are an important component, and an air conditioner with damaged fins will not perform as well.

4. Add Blocks and Weatherstrips

If your AC doesn’t sit perfectly level in your window you’ll need to install blocks. Set the air conditioner in the window and check with a level to see if it’s tilting to one side or the other. It’s common to need to add wood blocks to the front or back of the window frame to get the AC unit to sit level in the window.

Now is also a good time to add weatherstrips if you want to. Weatherstrips help take up excess room between your AC unit and the window frame, making your window airtight and eliminating leaks that make your AC work harder to keep your room cool.

Attaching weatherstripping is easy. Peel the cover off the adhesive backing and apply the weatherstrips to your windowsill. If you have enough room, you can also apply weatherstrips to the top of your air conditioner.

5. Attach Support Brackets

Some window air conditioners come with support brackets that secure the unit in place. If your AC unit comes with support brackets, install them by drilling pilot holes and screwing them to your window frame.

Some support brackets need to be screwed into your home’s exterior below the window. If you don’t want to drill holes in your home’s exterior, look for an air conditioner that uses leverage to wedge the support bracket against the exterior wall without the need for screws. These brackets are nearly as supportive as the screw-in kind and have the major bonus of not potentially damaging your home or its siding.

If you’re using a support bracket, refrain from tightening the screws fully until after the air conditioner is installed. Pre-tightening the screws might make it difficult to install the AC or prevent it from sitting in the window properly.

6. Place the AC Unit Inside Window Opening

With the support bracket in place and the weatherstripping attached, you’re finally ready to place the AC in the window. Carefully rest the air conditioner in your window, taking your time to avoid crushing any fingers or damaging your window frame.

Once you have the AC sitting firmly in the window, check that it’s level again. Sometimes installing wood blocks and support brackets changes how the unit sits, making it necessary to make minor adjustments to achieve the correct alignment.

7. Secure with Screws and Support Brackets

If you’re sure your air conditioner is level, secure it to the window frame and air conditioner support brackets by tightening the screws. Tighten the screws gradually, moving from one screw to the next intermittently. You don’t want to tighten one screw all the way before tightening the others since that can cause uneven stress on them and lead to problems down the line.

8. Fasten the Accordion Panels with Screws

With your AC firmly in place, extend and fasten the accordion panels to your window. Most window air conditioner installation instructions tell you to screw the accordion panels to your window frame, and we recommend taking this route if you’re not averse to drilling holes in your window.

Some units don’t come with screws and instead have clips that hook around your window frame. Generally speaking, screw-in accordion panels provide a better seal than clip-in ones, keeping more cool air in and letting your AC work more effectively.

9. Attach Foam Insulation Strip to Fill Gaps

Inspect the edges of your air conditioner to see if there are any gaps between it and your window frame. It can help to take a step back when looking for gaps, especially if you’re installing the AC during the day. Spotting small gaps is easiest when there’s a significant difference in the light level between the room and outside.

If you notice any gaps, you should fill them with foam installation strips. If you measured your window correctly and attached weather stripping, you probably won’t have any gaps to worry about.

10. Attach Unit to Electric Connection

And now for the moment of truth. Plug in your air conditioner and make sure it functions correctly. We recommend leaving the unit on for at least 30 minutes to see if it’s working correctly before making a judgment.

If your room feels cool after 30 minutes, you’re done! If not, check the outlet to make sure it doesn’t need to be reset. Barring any electrical problems, you might have to bite the bullet and exchange it for a new one.

Once you’re sure the AC is working correctly, make sure there are no refrigerant leaks and set up any advanced features like wi-fi connectivity. Most window ACs come with remote controls, so don’t forget to pop some batteries in and test it if you have one.

If you need to plug your air conditioner into an extension cord, make sure you have a heavy-duty cord rated for use with appliances. Ordinary extension cords are not safe to use with powerful appliances like ACs.

Considerations for Window A/C Installation

Before you head to the store to purchase a new window air conditioner, here are some things you should think about.

DIY vs. Professional Installation

Most people are capable of installing a window AC unit themselves, but they can be heavy and unwieldy, making it hard to do by yourself. It’s incredibly easy to lose hold of a window AC, and dropping it on your foot or crushing a finger is a great way to put a damper on the start of summer.

If you don’t have someone who can assist you in installing a window AC unit, you might want to consider hiring a professional.

Your best bet if you want to hire a professional is to ask the retailer when you purchase the air conditioner. Most stores that sell window ACs will offer a professional installation option, and even the stores that don’t offer in-house professional installations will be able to help you find someone who does.

Find a local contractor near you to get help with installing your window air conditioning unit.

AC Unit BTUs

The physical size of your AC is important — it needs to fit in your window, after all — but so is its capacity for cooling. An air conditioner’s ability to cool a room is measured in British Thermal Units or BTUs. In general, the larger the room you want to cool, the higher the BTU rating you need.

Determining the amount of BTUs you need to cool a room depends on the room’s square footage but also other factors like the number of windows and doors and how high the ceilings are. The following table estimates the number of BTUs an air conditioning unit should have to effectively cool a room based on the room’s size in square feet. The estimates assume a standard 8-foot ceiling and an average number of windows and doors.

Room Size (Sq. ft.)	AC Capacity (BTUs)
Up to 150	5,000
150–250	6,000–7,000
250–350	7,000–10,000
350–450	10,000–14,000
450–550	14,000–18,000
600–800	18,000–22,000
800+	25,000

Home and Window Age

If your home is on the older side, you might want to consider choosing a slightly more powerful air conditioner than you would if your home was new. Old homes have more leaks than new homes, as window and door seals wear out over time. If your air conditioner can’t cool your room as fast as the cool air it generates escapes through gaps in your windows and doors, you’re going to be disappointed (and sweaty).

You can solve the leaky-air problem by replacing your windows every 15–20 years. If your windows are old, be prepared to get less out of your new AC than you expect. Replacing your windows is expensive, but studies show that tightly sealed windows have a tremendous effect on a home’s energy efficiency by making it easier to cool in the summer and easier to heat in the winter.

Window Size, Style, and Material

Not all window air conditioners work with every type of window, so make sure to check what type of windows an AC works with before you buy one. The most common types of windows you might find in your home are sliding windows, double-hung windows, and casement-style windows. Most window ACs will clearly state what kind of windows they work with on their packaging or in the product description if you’re shopping online.

What material your window is made from won’t affect the type of window AC you purchase, but it can affect what tools you need to install one. If you prefer not to drill holes in your window frame, your choices for a window air conditioner will be limited.

Final Thoughts

A window air conditioner is an excellent affordable option for people who don’t want to deal with installing a permanent air conditioner in their home. The best window ACs from top brands like Frigidaire and Midea are easy to install, reasonably priced, and work in most common windows, so you shouldn’t have too much trouble finding one that works for you. Before you purchase any air conditioner, make sure it’s certified by Energy Star, an EPA program that promotes energy efficiency in home appliances.

Installing a window air conditioner is a straightforward process, but there are a few gotchas you need to look out for. If you take your time and follow the instructions in this guide and the information in your installation kit, your window AC installation should be a quick and painless process.

Other Window Resources