How To Install A Window AC Unit In A Horizontal Sliding Window

You can’t install a window air conditioner that are traditional in casement or sliding windows. What you need is an air conditioner for a horizontal sliding window.

Most horizontal window units are a little expensive than window ac units that fit in double-hung windows. The good thing about them is that they have added features, including programmable thermostats, multiple fan speeds, and WiFi capabilities. You also don’t have to modify your windows during installation.

If you’re on the market for the best sliding window ac unit, here is a review of the top six options on the market today.

Best Air Conditioner For Horizontal Sliding Window Comparison Table

How Horizontal Sliding Window Air Conditioners Work

Sliding window air conditioners, also known as casement ACs, are quite different from traditional air conditioners. They work from left to right, and the side-by-side casement sliders tend to conflict with each other. That means you can open both sides. If you happen to have horizontal sliding windows, we recommend using a slider air conditioner.

Air conditioners that fit in sliding windows don’t have a vertical orientation, and they are longer and taller than the typical air conditioners. They have a size of 20 inches and above. They also feature precut fasteners and inserts, which help to hold them in the window frame firmly. 

Not only do the fasteners and inserts help your air conditioning unit stay in place, but they also alleviate the need to buy and installing plexiglass or foam insulation to block any available open space. Sliding window air conditioners are specially designed to work with windows that slide from left to right.

This is why they are only a few of them in the market, although they are slowly becoming more popular. The good thing about casement air conditioners is that they are designed to be installed within a window space. 

After securing the air conditioner into place, its first job will be to get air within the room by starting a blower and activating its compressor. As the compressor keeps running, a cooling coil will start dropping the temperature. The blower will then pull air from the room, which will first move to an air filter to eliminate all the unwanted particles and dust. The air will then pass through the cooling coil and drop the temperature before blowing back into the room. 

The only difference between a sliding window air conditioner and the traditional air conditioning unit is the installation method. These AC units are vertically structured to support the horizontally sliding windows. Their major drawdown is that installing them can be quite tricky.

Horizontal vs. Vertical Sliding Window ACs

When shopping for an air conditioner for your window, it’s easier to find the ones designed for windows that open up and down. Most air conditioners are primarily intended for vertically sliding windows. The good thing about them is that they are easy to install because they only rest without any need for support. They also have a horizontal rectangle shape, although you can find them in different sizes. That means you have to determine the room’s size to cool and compare it with the air conditioner.

You need to purchase a vertically-oriented window air conditioner for horizontally sliding windows, although they tend to be taller and skinnier than the standard air conditioning units. One important factor you need to keep in mind is that there isn’t any specific standard for casement air conditioners. Before you buy any sliding window air conditioner in a local hardware store, you need to take proper measurements to ensure you have the right size to fit your window. 

What’s the Most Ideal One?

 That’s a tricky question to answer, although it can be simplified by saying it all depends on the type of window you’re using. If you have a standard window, then a traditional air conditioner is the right option to consider.

However, if you have a window that slides left to right, you need a sliding window air conditioner to cool your room effectively. It’s always good to buy an air conditioner compatible with the type of window you have in your home/room where you want a cool breeze. 

Pros and Cons of Sliding Window Air Conditioners

Sliding window ACs come with their advantages and disadvantages. Understanding them correctly will save you the trouble of trying to decide whether they are worth it or not. Here are some of their pros and cons.


  • Sliding window air conditioners offer more support than horizontally sliding window air conditioners. These can be ideal when you’re living in a rental apartment with sliding windows.
  • Affordable – Sliding window ACs are also very affordable. They feature affordable prices, which makes them suitable to consider when you’re on a tight budget. 
  • Customizable – When it comes to customization, you can entirely rely on sliding window air conditioners. They are easy to customize to fit into the size of your window or your apartment’s location. They also come with convenient features like WIFI, remote control, and temperature sensors. 
  • Easy to install – Since sliding window air conditioners are usually installed in windows, you won’t have to worry about dealing with complications of new tech or hose systems when installing them. 
  • Another notable advantage of sliding window air conditioners is that their water easily drains out of the window itself.


  • Unattractive – Unfortunately, sliding window air conditioners don’t compliment your home décor. It’s nearly impossible to sugarcoat the bulkiness of these types of air conditioners. However, since they provide you with comfort and cooling your house, that’s the price you’ll have to pay.
  • Heavy – These are the types of units that you can’t easily move around since they are not lightweight. Because of the air conditioner’s weight, it can even become difficult to install them on your window. 

Check out other air conditioners including

Air conditioners for narrow windows

Air conditioner for Andersen crank windows

Best smart window air conditioners

Things to Consider when Choosing a Horizontal Sliding Window Air Conditioner

Thinking about buying a horizontal sliding window air conditioner? Here are important factors to consider.


Can you install a window ac easily? That’s a crucial question you need to ask yourself first before buying any window AC. Most of the window air conditioners in the market are specifically designed to fit into double-hung windows. That means you first need to measure your window’s dimensions to determine the ideal AC for it. The good news is that some window AC models are designed to easily install inside a custom-made wall with enough space for special mounting hardware.

Cooling Capacity

The cooling capacity of an AC should be the first thing you check before you buy it. The cooling power is measure in the British thermal unit (BTU), and it tells you how effective the air conditioning unit will be in a certain room. The higher the BTU, the more effective the air conditioner will be. BTUs can range from 5000 to over 20,000. Therefore, you should choose the BTU size suitable for cooling your space.


Window air conditioners require maintenance to keep them functioning properly. When outside debris and dirt accumulate in your AC over a long period, it can lead to damages. Therefore, you need to consider buying an air conditioning unit that’s easy to maintain. Try to at least clean your AC once or more times a year. You can use warm water and soap for cleaning, but it’s important to check the user manual first to avoid causing the AC any damages.

Electrical Needs

Since window air conditioning units are more powerful than other household appliances, it’s important to ensure the electrical system you have in place can meet your AC’s needs. Most of the room ACs consume around 115V to 220V circuits. Electrical needs include the voltage, amps, and watts of your window air conditioner. You can check all this information in the specification section of your air conditioner.

Energy Efficiency

The best-selling window air conditioning units are the cost-effective ones and not the central AC. Energy-efficient air conditioners cost, and they are also cheap to maintain. There are two essential to look for when searching for an energy-efficient air conditioner. They include:

  • The energy star rating: These air conditioners only use about 10% less energy than other models. Therefore, they end up saving you money while using them. 
  • The energy efficiency rating (EER) is the measurement that tells you the number of BTUs an air conditioner uses for every watt of power. Keep in mind that the higher the EER rating of central air conditioner, the more efficient it is. 

How to Install an Air Conditioner in a Sliding Window

Here are simple steps to install an air conditioner in a sliding window. 

1. Record the Measurements

The first and most crucial step is to record or take measurements of your air conditioner. Measure your AC’s width and ensure you include any vents that may be sticking out on the side. Once you’ve measured the width of your air conditioner, go ahead and measure the height. The height should be the box height without the lips on the bottom or top. Also, measure the window opening’s height.

2. Cut a Frame Lumber (window framing)

Cut the plastic curtain frame lumber 2 x 4 such as:

  • 3 – width (include vents) of your AC
  • 2 – the height of the window frame

3. Start the Window Frame

Lay the 2 x 4 piece down in a slight tilt and then use one or more screws from the ends of the longer pieces to the end of the shorter piece. Screw another piece of size 2 x 4 to create a rectangle between the longer pieces on end. Ensure that the corners are square.

Test the rectangle into your window track to check if it fits. It should adequately slide in and sit right against the window frame. 

4. Complete the window Framing

 The next step involves drying-fit your AC. Set your air conditioner into the plastic curtain frame, including the bottom lip, which should be right against the outside plastic curtain frame. Ensure the last piece of your 2×4 sits across the top of the shorter leg of the U. However, avoid screwing it in yet.

5. Cover the Top wooden frame

Measure the opening on the top of the frame and use plywood to cover it. Once you have the accurate measurements, take plywood that fits it perfectly and use it for the cover of the window sash.

6. Install the Air Conditioner

After you’ve completed the above steps, the final step is to install a window air conditioner. All you have to do is open your window and slide the AC inside it and up against the window frame.

Best Air Conditioner For Horizontal Sliding Window Reviews

1. Frigidaire FFRS1022R1 Slider/Casement Room Air Conditioner 

FRIGIDAIRE FFRS1022R1 10000 BTU 115-volt...
  • Specially designed for casement-window or sliding-window installation - installation kit included (Not suitable for standard-window installation)
  • 10,000 BTU air conditioner cools a room up to 450 sq. ft. with dehumidification up to 3.4 pints per hour (Uses standard 115V electrical outlet)
  • Multi-speed electronic controls with 24-hr. on/off timer and full-function remote control
  • Auto cool, Energy Saver mode, Sleep mode, 4-way air direction and washable mesh filter with check filter alert
  • Energy Efficiency Ratio (EER): 10.4
  • Window height- 21.5 inch minimum / 40 inch maximum. Minimum window width- 15.5 inch

The Frigidaire FFRS1022R1 horizontal sliding windows are a powerful window ac that is specially designed to fit casement windows between 15.5-16.25 inches wide and 20.5-40 inches high. It produces 10,000 BTUs of cooling power enough to cover rooms up to 450 square feet and can remove up to 3.4 pints of moisture per hour when used as a dehumidifier.

This window opening air conditioner has an energy efficiency ratio of 10.4, and it comes with a programmable thermostat that lets you select temperatures between 60 and 90 degrees Fahrenheit. The air conditioner also features an energy-saving operation mode that shuts down the compressor when the temperature levels match what you set. The window opening air conditioner will only turn the compressor back on when temperatures rise above your set point. 

This Frigidaire casement window unit also has a fan with three speeds and four-way air directional louvers that allow you to direct cold air to where you need it. 


  • It has a programmable timer
  • Sleep mode
  • Washable air mesh filter
  • Programmable thermostat
  • It is remote controlled
  • Operates quietly 


  • It doesn’t include a heat function
  • It is exclusively for casement windows

2. Frigidaire FFRS0822S1 Casement Window Air Conditioner

FRIGIDAIRE FFRS0822S1 8000 BTU Heavy-Duty Slider...
  • Beat the heat while remaining cool and happy on hot summer days
  • With 2344.57 W cooling power, enjoy a blast of cool air throughout your room
  • Effectively cools area of up to 350 Sq. ft., this air conditioner is perfect for bedrooms
  • Provides enough cooling in your room with 3 fan speeds
  • Full-function remote control allows you to precisely control the temperature and fan speed from across the room
  • Power source type: Corded Electric
  • Mounting type: Casement/Slider

The Frigidaire FFRS0822S1 ac unit is a powerful heavy-duty air conditioner ideal for spaces up to 350 square feet. It is specially designed for casement or sliding windows that are 15.5 inches wide and up to 40 inches high.

This 8,000 BTU window ac features a 24-hour timer that lets you set the window opening air conditioner to turn on or off as you please. This feature gives your home a cool breeze and comfortable all the time without the risk of running up your electricity bills. It also has an automatic restart feature that lets the air conditioner resume cooling with all previous settings in case of power problems.

This Frigidaire ac unit has washable antibacterial air filters that are easy to access for maintenance and a filter alert that notifies you whenever the filter needs cleaning. In addition to that, it features a fan with three speeds and 4-way air directional louvers that allow you to direct cool air to where you want it.


  • It doubles as a dehumidifier
  • It has an antibacterial air filter
  • 10.8 EER rating
  • It comes with a full-function remote control
  • Variable fan speeds and airflow directions


  • This ac is loud when the fan is on high speed.

3. Koldfront 115V Casement Air Conditioner with Dehumidifier

Koldfront CAC8000W 8000 BTU 115V Casement Air...
  • 8000 BTU vertical window air conditioner engineered for spaces ranging in size from 300 to 350 square feet
  • Designed to fit casement (left to right sliding) windows ONLY, and will not fit windows that slide up and down. Fits windows 15-1/2" to 16-1/4" wide with a minimum height of 21-1/4" when using the window panel retainer and a maximum height of 39-7/16" (minimum window height of 20-5/16" without the window panel retainer)
  • Digital Display; Dehumidifier; Sleep Mode; 3 fan speeds; Remote control with 16ft range; LCDI 5-15P plug type
  • Energy Efficiency Ratio (EER): 11.0 / Energy saver mode
  • Includes all installation hardware and weather seals

The Koldfront CAC8000W ac unit is a powerful casement window ac that is sure to keep the heat at bay with a long-lasting cool breeze. It produces 8,000 BTUs of cold air enough to chill spaces between 300-350 square feet, which makes it ideal for use in bedrooms and large living rooms and offices.

The air conditioner is energy-star certified because it has several features that ensure your space has cool breeze all the time without running up your electricity bills. These features include sleep mode, energy-saving mode, thermostat-controlled operation, among others. It also has a control panel with a digital display and a remote lets you operate the central air conditioner from up to 16 feet away.

The Koldfront CAC8000W Window ac unit is designed to fit in a window frame from 15.5 – 16.25 inches wide and a minimum height of 21¼ inches with the window panel retainer. Minimum height reduces to 20 inches without the retainer. It is easy to install, and it comes with all installation accessories and weather seals.


  • It dehumidifies
  • It has a 3-speed fan
  • Digital display with multiple settings
  • Energy efficient
  • It comes with a full installation kit and support bracket.


  • It does not have a timer.

4. PerfectAire 3PASC10000 Slider Window Air Conditioner

PerfectAire 10,000 BTU Slider Air Conditioner...
  • Adjustable temperature settings that range 62°F - 86°F (17°C - 30°C); cools areas between 400-450 sq. ft.
  • Expandable window mounting kit accommodates horizontal sliding or crank-out casement windows with a 15½”/16¼” (min./max.) window width and a 21¼”/39½” (min./max.) window height
  • 3-speeds in both cool and fan modes
  • Full function remote control with Follow Me portable thermostat technology for total room coverage
  • Front-mounted, tilt-out air filter access for easing cleaning

The PerfectAire 3PASC10000 is a 10,000 BTU window ac that can cool rooms up to 450 square feet. It is designed for casement windows with widths between 15.5 inches-16.24 inches and heights between 21¼ – 39½ inches.

This window opening unit features four operating modes that allow you to customize your indoor climate fully. These include a cooling mode, a fan mode, dehumidification, and auto, where the window opening unit chooses the best operating mode according to the natural climate changes in your space. It also has adjustable temperature settings that range between 62°F – 86°F.

The PerfectAire 3PASC10000 also has a removable and washable air filter that keeps your air clean and healthy. It also has an exhaust control to circulate air inside the room or push it outside.


  • It has four operating modes
  • It has washable filters
  • Three fan speeds and adjustable air louvers
  • Follow me remote feature
  • It has a check filter indicator.
  • Adjustable timer


  • This is a cool-only AC. It does not have a heat mode.

5. Global Industrial Casement Window Air Conditioner 

The Global Industrial MWDUL-10CRN1-BCJ4 is a powerful compact and energy-efficient window ac that can serve spaces up to 450 square feet. It has a powerful fan with three speeds and four-way air direction louvers which allow you to choose where to direct cold air.

This 10,000 BTU ac also features an auto-restart mode that restarts your unit with all previous settings intact in case power shuts down. Furthermore, you can set the window opening unit to sleep mode at night to maintain your preferred temperatures all night without consuming a lot of energy or disturbing your sleep.

In addition to that, it has an LED display that allows you to see the adjustments you make and a remote that lets you operate the unit from anywhere in the room.


  • It has adjustable speed levels
  • Cools a large area
  • It is remote controlled
  • It has an easily accessible washable air filter
  • It uses an eco-friendly refrigerant
  • Easy to install a window ac A full installation kit included and support bracket.


  • It is noisy at high fan speed.

6. Danby DAC100B1WDB 10,000 BTU Window Casement Air Conditioner

Danby DAC100EB1WDB 10,000 BTU Window Air...
  • Excellent Cooling Power: This 10,000 BTU window air conditioner with Follow Me Function quickly cools your room
  • Window air conditioner ideal for spaces up to 450 square feet
  • Powerful Air Circulation: Powerful 3 speed fan and 4-way air direction circulates the air in the room
  • Follow Me Function: Remote control acts as a thermostat allowing for more precise temperature control
  • Programmable Timer: This window unit air conditioner has a convenient 24-hour programmable timer
  • Comfort Sleep Mode: The Sleep mode prevents the room from getting too cold while you sleep
  • Modern Look: Electronic controls with LED display give a smooth modern look
  • Reusable Air Filter: The air filter is reusable and washable
  • Auto Restart: The air conditioner automatically restarts after a power failure

The Danby DAC100B1WDB window air conditioner contains 10,000 BTUs of cooling power perfect for chilling spaces up to 450 square feet. It is designed to fit casement windows that are 15.4 inches wide and have heights between 20.9 – 39.6 inches.

This unit has a powerful 3-speed fan and four airflow directions that allow you to direct the cold air to where you want it. It also features electronic touch controls with LED display and a full-function remote to give you total control of your indoor climate. 

This Danby Casement horizontal window unit is energy-star rated, and it is equipped with several features that keep your electricity bills low. You can set the 24-hour timer to turn the unit on and off as you please, and you can enable “sleep mode” at night to let the air conditioner adjust the temperatures all night to keep you comfortable as you sleep.

The Danby DAC100B1WDB is easy to install, and a full installation kit comes with the package and support bracket. In addition to that, Danby offers you a 12-month warranty on parts and labor.


  • It has a full feature remote control
  • 24 hr. programmable timer
  • Sleep mode keeps you comfortable while saving energy
  • It has removable and washable filters
  • Easy to install a window ac(full installation kit included and support bracket)
  • 12-month warranty on parts and labor


  • This ac unit lacks intrusion protection and an insect barrier.

Wrap Up

Cooling your space using an air conditioner for a horizontal sliding window doesn’t have to be complicated. The products I’ve reviewed above delivers unrivaled cooling to both residential and commercial spaces.

Remember, this is a guideline, and you should determine the size of your room to help you pick the right BTUs for your sliding window air conditioner.

You should also consider the size of your window since casement/horizontal windows are more narrow than double-hung windows.