Best Sliding Window Air Conditioners in 2021

Just because you don’t have crank or casement windows, it doesn’t mean you can’t still install an air conditioner in your room. You may just be pleased to discover that you have another option to stay cool and comfortable this summer.

Ordinary window air conditioners are typically designed for double-hung windows. And with that, many homeowners simply do not think that their vertically structured AC units can actually accommodate sliders and casements. Casement AC units come in all shapes and sizes, and they are designed to fit within a window that slides from side to side or one that cranks outwards.

A slider or casement air conditioner is what you’re ought to be looking for if you need a window air conditioner that fits into a sliding window. Not every window air conditioner is going to fit into one. Casement air conditioners start from 20 inches in height and above and they come with pre-cut inserts and fasteners to hold the window air conditioner unit in the window frame. On top of helping your unit stay in place, these pre-cut inserts also eliminate the hassle of buying and installing Styrofoam or plexiglass to block any open space.

With numerous casement AC units available on the market, it can get confusing on deciding the best sliding window air conditioners for you. With that in mind, we have prepared this buyer’s guide that will provide you with everything you ended to know about the best sliding window air conditioners: the factors to picking one as well as a review of the best sliding window air conditioners you can get your hands on now to help you stay cool in the summer months.

Aspects and Factors to Consider when Buying a Vertical Sliding Window/Casement AC Unit

Before choosing your sliding window air conditioner, here are a few qualities that you need to consider:

Cooling Power vs Area Coverage

The first thing to look into is, of course, the window air conditioner’s cooling effectiveness. You can easily hit it out of the park on every other important aspect of a window AC, but what’s the point of buying one if it does not cool the way you need it to?

You can’t expect to stay adequately cool and comfortable in a large space with a tiny AC unit. On the other hand, there’s also no need for you to get a massive casement AC if you need to cool a room that’s only 100 square feet in size. Properly sizing your AC doesn’t need to be a guessing game, and it shouldn’t be.

Window air conditioners typically have a cooling capacity ranging from 5,000 to 12,500 British Thermal Units (BTU). As a general rule of thumb, you’ll need a cooling capacity of 20 BTU for each square foot of living space. This means that a 200 square feet room will need a 4,000-BTU AC unit.

Size & Weight

Just because it’s compact, doesn’t mean they’re light. Don’t ever let their compact size fool you as these window ACs are a whole lot heavier than you might think. Generally speaking, the higher the BTU, the greater the size and weight it is. When it comes to the size, you need to remember to take measurements of both the width and height of the window so that the installation doesn’t lead to any unpleasant surprises.

If you choose an AC unit that’s greater than 8,000 BTU, you need to plan ahead and expect installation to be a 2-person job. If that’s not an option, it’s better for you to opt for an AC unit that has a lower BTU rating, or choose two smaller units that are lighter in weight. Considering the weight and size is not only about selecting a unit that the window frame can handle, but also one that you can work and handle with.


While shopping for your new sliding window AC unit, the placement of the air conditioner should always be on your mind. Location within your home is a huge determining factor for which specific models you buy. For example, if you want to cool down a room on the second story that is hit with direct sunlight most of the day, you’ll want to purchase a more powerful unit with a high BTU rating to effectively cool your room down.


One of the first few steps in the air conditioning process is the air filter. The AC takes air directly from the room and filters out dust and other unpleasantries, like allergens and bacteria, before cooling it down. Some AC units come with an outstanding filtration system that even works to purify the air within your home, while others may not have this functionality.

Choosing a model that effectively filters out contaminants can prevent health and breathing issues down the road. Some AC units also come with reusable and washable filters but do note that others will need to have their filters replaced when the time comes.

Another useful function that only the best sliding window air conditioners provide is the dehumidification feature. These air conditioners work to dehumidify the air by bringing down the moisture levels within the room. The main advantage of dehumidification is that it maintains healthy air humidity levels, which can help with:

  • Improved air quality
  • Mold prevention
  • Elimination of dust mites
  • Protection of the home’s structural integrity
  • More comfortable living space
  • Efficiency

The overall efficiency of an AC unit is measured by the energy efficiency ratio (EER). This is calculated as the ratio of the cooling capacity (in British Thermal Units (BTU) per hour) to the power input (in watts). The higher the EER rating, the more efficient the air conditioner is. Another reliable method to determine whether the AC unit is efficient or not is to look for the government-approved ENERGY STAR label.

Air Speeds, Programmability & Timed Cycles

Some sliding window air conditioners come with multiple airspeeds, while others may just have one airflow setting. The ability to allow you to control multiple airspeeds is important, though it’s not necessarily essential. Multiple airspeeds mean that you’ll be able to achieve maximum comfort, no matter the weather conditions.

A sliding window AC unit with programmable timed cycles is also another cool feature that will maximize the unit’s versatility. Programmability allows you to switch the AC off after you’ve fallen asleep for the night, or to turn it on before you arrive home from work. This function also adds to the machine’s efficiency since you can time it to turn off whenever the air conditioning is not necessary.

Noise Levels

Noise level is another huge factor to consider, especially if you plan to install this AC in your bedroom. The best quiet window air conditioners typically have a decibel rating between 40 and 60. Window air conditioners are installed such that they’re partially inside the home as well as outside, so the noise will be dispersed in both directions/ But even so, it is advisable for you to read reviews of the best sliding window air conditioners to find out each unit’s average noise level.

Ease of Installation & Maintenance

Installing a window AC unit can be a DIY project that does not require the help of a professional. That being said, there are some AC units that are easier to install than others. Casement air conditioners tend to be bulky and heavy, so choosing one that has easy installation steps is a must. You’ll also want to find one that is easy to maintain and does not require frequency servicing.


Even though window air conditioner units are much more affordable than central air conditioners, you don’t have to give up on the idea of reliable warranty coverage. Some manufacturers offer better warranty policies than others. The trick here is to not only focus on the length of coverage time but also pay attention to the specific parts, pieces, and defects covered by the policy.

Advantages and Disadvantages to Vertical Window Air Conditioners

Vertical window air conditioners obviously have a number of amazing qualities, but as with any air conditioning unit, they do come with some drawbacks. Here are some of their most noticeable pros and cons:



If you’re renting a home or apartment without a central AC system, vertical window air conditioners are one of the best solutions to help you overcome the heat. Obviously installing central AC in such a circumstance is often not an option, and window units are one of the most affordable ways to prevent roasting inside your home every summer.


With so many types of models and designs out there, it will certainly be simple for you to find a vertical window AC unit that fits your needs in terms of window size and location. Plus, some air conditioner models even provide you with handy features, such as a remote control, Wi-Fi, or temperature sensing ability.


Since these units are installed in windows, you need not worry about having to rig up some complicated new electrical and hose systems like you would need to do with a standing indoor AC unit. The water for these sliding windows units can just drain right out of the window itself.



Vertical sliding window AC units are not exactly the most attractive home decor available and it can be pretty difficult to sugarcoat how bulky these units can be. Of course, aesthetics is really a small price to pay when it comes to staying cool and comfortable in hot summer months, plus you also have the option to remove the sliding window AC when it’s not the peak of summer.

Complicated Installation

These air conditioning units can be heavy and complicated to install, so uninstalling and reinstalling every year may not be the most viable option for a lot of folks. Another thing to consider is that a sliding window AC unit requires actual insertion into your window, meaning your window will need to be left open to a certain extent.

Less Security

The fact that you need to leave your window open can also mean that you’ll allow hot, humid outdoor air to pour into your room and cool air to escape. Other than that, it also leaves your home more vulnerable to potential security threats. Though you can mitigate this with some insulation and other types of sealing, you can’t really get around the fact that on some level, this will make your home less secure.

Horizontal vs Vertical Window AC

Some may wonder why vertical window ACs are a thing since a horizontal window unit will make more sense in a sliding window situation. However, gravity will play a role and exert a different kind of pressure on a window unit that is placed in a horizontally-open window than one that is placed in a vertically-open window. For this reason, more and more people are incorporating vertical sliding window AC systems in their new homes and instead of horizontal sliding window models.

An air conditioner that’s installed in a vertical sliding window will have more support on either side to hold it in place whereas one that’s installed in a horizontal sliding window will not have that support, and as a result, tend to tip outward. In order to prevent this, you will either need a unit that substantially protrudes into the room or a block of wood or some other type of support system outside of the window, which may not be a viable option for those living on the second story.

In this case, you can clearly see how a vertical window air conditioner makes far more sense. If you have the option of picking between a vertical sliding window and a horizontal sliding window AC, you should always go with the vertical one.

Review of the Best Sliding Window Air Conditioners in 2021

Now that we have spent some time talking about the basics of sliding window air conditioners, here are some brands that have done their job well and have been positively received by many homeowners alike. In the review below, we will talk about their features as well as touching upon different aspects like BTU rating, remote control features, fan speeds, and more to help you decide whether it’s the one for you.

Best Overall

1. Frigidaire FFRS0822S1

Among many other things, this window air conditioner really stands out to us because of its amazing dehumidification feature. Rooms can get really stuffy and develop bad smells after a couple of days away from it. This situation can get worse with humidity as it will give rise to algae and moss, making the room unbreathable.

To help reduce the humidity effects in a room, this portable air conditioner has the ability to remove more than 3 pints of water from the air per hour to keep the room dry and comfortable.

This air conditioning model comes with a relatively lower BTU, however, it is compensated by a good SEER level. The window air conditioner isn’t very big in size either, making it easy to install for most. Moreover, it reduces the energy consumption of the model which makes it economical in the long run. The unit requires 115V power to run and has the ability to cool rooms up to 350 sq ft.

Reviews online prove that buyers have only positive things to say about this product as it comes with all the features they need without the expensive price tag. Some of the features include a perfect remote control that gives them control over the temperature settings without needing to get up. They also praise the diverse settings that appear on the AC that gives them more control over the temperature they want inside the room.

Bottom Line

With an impressive energy SEER and better humidification factor, this window AC model is already making rounds in the industry as one of the most reliable window AC units available. This is further assured by the company’s better overall warranty and high-end construction of the model to increase the faith of buyers towards the model.

You would like this if:

  1. You want one that comes with double-wall thickness for more durability
  2. You want a higher relative warranty to make the model more reliable
  3. You prefer significant lower noise levels than most other models
  4. You want a remote control that comes with a range of settings

You might not like this if:

  1. You don’t want a time-consuming installation process
  2. You don’t want something which is relatively heavier than most other models


2. PerfectAire 3PASC10000

Featuring four different operating modes, this sliding window air conditioner unit enables homeowners to fully customize their desired climate. It offers dehumidification, auto, a cooling mode, and a fan mode. It is even able to gauge the natural climate changes to determine which operating mode will best suit your needs. Additionally, it further features a washable and removable air filter that will ensure healthy and clean air all year round.

This 10,000 BTU slider window air conditioner can cover areas of up to 450 square feet. It’s also programmable for you to time it to switch off and on by itself, making it the perfect choice for those who want to conserve energy or want to cool the house down before they return. However, one slight drawback is that its operation may be a bit noisy and hence not be suitable for the bedroom if you’re a light sleeper.

Nonetheless, the majority of the buyers were extremely satisfied with their purchase and particularly loved how the functional remote control doubles as a thermostat. Although some users found the unit’s operation to be a bit noisy, most stated that the AC unit is easy to install and cooled the room well.

Bottom Line

This PerfectAire model easily fits in architectural windows, eliminating the need for costly custom designs, and can cool rooms measuring up to 450 square feet. With three fan speeds, full-range direction control, and adjustable temperature settings, this sliding window unit will allow you to easily find your comfort zone.

You would like this if:

  1. You prefer tilt-out air filters that allow easy cleaning
  2. You want a window air conditioning unit that comes with three speeds in fan and cool modes
  3. You want adjustable temperature settings with a range of 62°F to 86°F
  4. You like to have a portable thermostat technology to ensure total room coverage
  5. You want to cool areas measuring between 400 and 450 square feet effectively

You might not like this if:

  1. You don’t want a noisy operation
  2. You want a heat mode

Best for the Money

3. Keystone 5,000 BTU 115V Window-Mounted Air Conditioner

The Keystone 5,000 BTU 115V Window-Mounted Air Conditioner is an excellent product that can effectively cool almost any room, even ones that are not the standard square or rectangular shape.

One of the coolest things about this slider window air conditioner unit is its remote control, which comes with a temperature sensing “follow me” option that essentially allows the unit to read the temperature wherever the remote is and adjust its settings accordingly. Most units can only read the temperature where the unit is actually placed. With this option, you can now carry the remote around with you and the AC unit will adjust the temperature whenever you are.

Other than that, this sliding windows unit also comes with a number of other convenient features, including the ability to shut off the lighting on the unit’s interface so that it will not glow obnoxiously at night and interrupt your sleep.

Bottom Line

The Keystone 5,000 BTU 115V Window-Mounted Air Conditioner is an effective model that will cool where you are and not just where it is. However, it does have a more complicated drainage system which you will need to take note of during installation.

You would like this if:

  1. You want a quiet model that is easy to install
  2. You want a sliding window air conditioner that will not increase your electric bill
  3. You want a unit that cools more effectively than you would think based on its size
  4. You like to have the option to upgrade to an energy star, which comes with additional insulation

You might not like this if:

  1. You don’t want to deal with a complicated drainage system that drains poorly
  2. You want easily adjusted vents

Best Casement Window Air Conditioner

4. hOmeLabs 5000 BTU Window-Mounted Air Conditioner

The hOmeLabs 5000 BTU Window-Mounted AC is a fantastic unit that will get the job done no matter which room it is installed in. Disclaimer – this unit is too small to be able to cool a large apartment or the entire house, but it is definitely good enough to cool spaces such as master bedrooms or children’s bedrooms.

One highlight is that the control panel interface does not light up, meaning you won’t have to worry about obnoxious glowing lights at night that will interrupt your sleep. This unit also comes with four different settings: two fan settings and two cooling settings. This powerful AC unit is able to cool your entire room even when it’s set to the lowest setting – we guarantee you’ll be impressed.

You will be even more impressed to know that this unit has no significant impact on your electrical bill as users report a slight bill increase of about $40 even when they’re running the unit continuously. This is a small price to pay for ultra comfort in the blazing heat of the summer.

Finally, this casement window AC unit is incredibly easy to use. Installation, filter changing, and everything else about this window AC is simple and easy to figure out.

Bottom Line

The hOmeLabs 5000 BTU window-mounted Air Conditioner is a great AC product that can help you cool a room within your larger apartment or home. However, due to its size, don’t expect it to be able to cool much beyond that.

You would like this if:

  1. You want a quiet unit
  2. You want a good and durable unit that is suitable for smaller areas
  3. You want one that is good at dehumidifying a room
  4. You want a filter that is easy to remove and clean

You might not like this if:

  1. You want a timer that can be programmed to shut off automatically

Best Casement Window Seal

5. HOOMEE 400

The main purpose of a portable AC is to increase the cooling in your room while ensuring a properly balanced distribution of cold air in all corners of your room by not allowing the air to escape through the gaps in the window.

The AC also zips around the nozzle of the hose and blocks any kind of warm air from returning. This, coupled with better efficiency, helps ensure that people sitting in all corners feel an equal amount of cold.

Unlike other models, this one does not come with a restriction of size and it can fit around most casement windows with a maximum distance of 400cm between the panels. There are many reasons why this seal is considered to be one of the best.

The top reason being its ability to help regulate fuel consumption. Another reason why this is appreciated by buyers is that it’s a cost-effective model that lowers the electricity bill in the long run.

Bottom Line

With so many amazing features at its disposal, this air conditioning unit surely had to be included on our list. It comes with high-end construction that offers better durability and strength. Plus, it also offers easier installation and does not require a professional to do it. If you want to increase the efficiency of your AC, then this window seal will fit the bill perfectly.

You would like this if:

  1. You want to prevent the entry of any additional hot air from all sides
  2. You want an easy installation with the help of a thorough guide
  3. You want the ability to lock the hose between your window frames
  4. You do not want to buy additional tools for installation
  5. You want better controls

You might not like this if:

  1. You don’t want to have frequent cleaning

6. LG Energy Star Window Air Conditioner

The LG Energy Star Window Air Conditioner is a fantastic sliding windows unit that will make your life a thousand times easier thanks to its Wi-Fi control option. Once you’ve downloaded the LG SmartThinQ app on your smartphone (iPhone and Android model compatible), you will be able to use Wi0Fi to adjust your air conditioner’s fan speed, temperature, mode, and even the option to schedule an automatic timer to shut down or start up the AC unit.

If you’re more old-school or less tech-savvy and prefer the unit’s manual features, there are also a number of options for you as well. The indoor vent points upwards and circulates the cool air throughout the room instead of just blowing it straight out as most front-facing vent would do. The outdoor vent can also be closed in order to block out any unpleasant outdoor smells if you happen to live in a city. Best of all, the Energy Star economy mode will work even on extremely hot days when electric companies lower the amount of available power.

Bottom Line

The LG Energy Star Window Air Conditioner is a great unit with incredibly convenient aspects to make your life better. Though it may take a little longer to set up, this is because the instructions are not very specific. However, once you have it up and running, you will be able to enjoy a cool and comfortable environment even on the hottest days.

You would like this if:

  1. You want an AC unit that is quiet and easy to use with strong energy efficiency
  2. You want to cool spaces quickly
  3. You have smaller rooms

You might not like this if:

  1. You want smoother installation with helpful instructions

7. Frigidaire FFRS1022R1 1000 BTU 115-Volt Slider/Casement Room Air Conditioner

Frigidaire offers a range of casement window air conditioning units and this is a 10,000 BTU AC that can cool a room about 450 sq. ft. In addition to that, this unit plugs into a standard 115V electrical outlet and can pull up to 3.4 pints of water out of the air per hour.

Other features of the slider window AC unit include multi-speed electronic controls with 24-hr on/off timer and a full-function remote control. It also has auto cool, energy saver, and sleep modes with four-way air direction and a washable mesh filter with a “check filter” alert.

The air conditioner unit fits sliding windows with a minimum height of 21.5 inches up to 40 inches and must be at least 15.5 inches wide. Aside from that, Frigidaire provides a limited 2-year warranty and a 3-5 year warranty on a sealed system.

You would like this if:

  1. You want a kit that provides a good range of window sizes it will fit in
  2. You have a narrow room as this unit outperforms its BTU rating

You might not like this if:

  1. You don’t want to drill an additional hole at the bottom for better draining of water and to avoid the fan splattering water

8. Global Industrial Casement Window Air Conditioner 10,000 BTU

This decent 10,000 BTU air conditioner unit from Global Industries will definitely meet your needs for a room around 450 sq. ft. This AC also runs on 115V and has a four-way air direction control fan to help cool the whole room evenly.

Furthermore, it comes with a washable filter, so that you won’t ever need to worry about replacements until you’ve really worn that one out. This sliding window air conditioner can be operated by remote control. Other features include auto restart, sleep mode, and a 24hr on/off timer for your convenience.

Bottom Line

On top of being a reliable air conditioner for your sliding window, Global Industries even offers a 1-year parts & labor warranty and a 5-year sealed system warranty to protect you from any defects.

You would like this if:

  1. You want an AC unit that comes with a support bracket for smooth installation
  2. Cooling capacity is often more than promised by the manufacturer

You might not like this if:

  1. You don’t want a unit that gets noisy at times

9. Koldfront CAC8000W

This Koldfront CAC8000W AC model’s control panel is its novelty and offers users plenty of settings to achieve their ideal comfort. It comes with a very easy-to-see and operates digital display. Unlike other models, the buttons on the control panel aren’t very small and are visible from afar too.

Moreover, the slider window air conditioner comes with different fan speeds that can control the airflow inside the room, allowing those residing in the room or RV to easily change the fan speeds according to their preference. The unit also has a noteworthy dehumidification ability.

The sliding windows unit is made for those who want cost efficiency and speed efficiency at the same time. It comes with 3 different fan speeds and a 16 ft range remote control for you to make use of these air conditioners even in larger RVs.

Moreover, this window unit is not very tall, which makes installation easy. This unit can cool rooms of about 350 square feet, making it suitable for a range of RVs alongside other rooms. What most recent buyers are thrilled about is that this unit is cost-efficient in the short and long run as it has a high SEER. They also love that it is extremely compact, making it easily portable.

Bottom Line

This portable air conditioner helps you keep the summer heat aside and lets you enjoy non-stop and never-ending cool breezes indoors at all times, even inside your RV. This compact air conditioner is one of the easiest units to install and does not require additional hardware. It also comes with good BTU energy efficiency, but the main reason why most people will opt for this window model is because of its relatively lower price.

You would like this if:

  1. You want 16 ft to range remote control for better customization
  2. You want a unit that features different speed levels and a sleep mode
  3. You want a unit that comes with all the installation hardware you will need
  4. You want relatively higher energy efficiency than most models

You might not like this if:

  1. You want a higher BTU
  2. You don’t want to pay too much for the repair and replacement of parts

10. Frigidaire FFRA0511R1 5,000 BTU 115V Window-Mounted Mini-Compact Air Conditioner

The Frigidaire FFRA0511R1 window air conditioner is an awesome window unit that fits into smaller spaces compared to many other window AC units out there. Its size makes it a convenient choice for a number of reasons other than easier installation and manipulation. This unit is also simpler to remove and easier to stow away in a storage area during the winter months to keep your house better insulated.

While you may not like the idea of always installing and reinstalling your AC unit, users of the Frigidaire Mini-Compact have reported that the whole process of installing and uninstalling will only take fewer than twenty minutes. Also, it will not take up a lot of space wherever you end up storing it thanks to its smaller size.

As another bonus, its compactness will ensure you do not need to use an outside supporting bracket to mount to your window. But just because it’s tinier doesn’t mean that it won’t function as well as the other window units. This model has two fan speeds, two cooling speeds, and two-way airflow – there is simply not much that this unit will not be able to do.

Bottom Line

The Frigidaire FFRA0511R1 5,000 BTU 115V Window-Mounted Mini-Compact Air Conditioner is great for sliding windows. Though its smaller size makes it very convenient, it may struggle to cool larger areas.

You would like this if:

  1. You want a quiet and lightweight unit that is easy to install
  2. You want a window AC that rapidly cools areas
  3. You prefer smaller size models that make for easier storage

You might not like this if:

  1. You need to cool large spaces

11. Frigidaire 5,000 BTU 115V Window-Mounted Mini-Compact Air Conditioner w/ Mechanical Controls

This Frigidaire model is an excellent air conditioner unit that keeps it old school with its use of mechanical controls on the control panel. If you’re old school and do not want to pay extra money for remote control or a Wi-Fi system that you will never use, then this is the air conditioner for you.

Its mechanical control system has two cooling speeds and two fan speeds. The unit also comes with adjustable vents to send cool air in any direction you want, so you do not have to worry about this unit being able to cool only what is directly in front of it. It is also a hardy little conditioner that will last you a very long time.

Another bonus to the mechanical controls is that not only is this unit simple to operate, but it is also quite easy to set up. Many owners report that it took them less than ten minutes to set it up and running. There is really not much to dislike about this Frigidaire model.

Bottom Line

The Frigidaire 5,000 BTU window-mounted mini-compact AC is a great air conditioner that is straightforward and easy to operate. Keep in mind though, that it does not have a thermostat for reading the actual temperature of a room.

You would like this if:

  1. You want a durable unit that can quickly cool rooms
  2. You want an energy-efficient model to keep the electric bill low
  3. You prefer mechanical controls that are simple to operate
  4. You want an easy installation that takes less than ten minutes

You might not like this if:

  1. You don’t want a heavy unit
  2. You want one with a thermostat

12. Koldfront WAC12002WCO 12,000 BTU 115V Window Air Conditioner

The Koldfront WAC12002WCO is a leader in energy-efficient sliding window AC models. Despite its high BTUs, this unit only uses 1000 watts. That means that you can keep this unit running 24.7 for a full 30-day cycle and your energy bill would only increase by less than $100, making this unit less expensive than a central air system!

Don’t even think for a second that this efficiency comes with a compromise on its effectiveness – this AC is able to cool an entire room within thirty minutes, and eventually even cool off an entire house. All this with 12,000 BTUs, also known as the highest BTU rating a “normal” outlet can process. So, you don’t have to install new 230V outlets.

This unit also serves as an excellent dehumidifier with the capability of removing several pints of water per hour from your room’s air. If you live in Florida, this might just be the best AC for you.

Bottom Line

The Koldfront WAC12002WCO is just about the most energy-efficient AC out there. However, it might not be as cool as some of the other models.

You would like this if:

  1. You want a model that is quiet and easy to install
  2. You want an AC that’s made of high-quality material and can be controlled remotely
  3. You want a unit that still produces a large amount of cool air on the lowest setting

You might not like this if:

  1. You prefer colder environments as the lowest setting is 62 degrees

Unique Challenges of Sliding Windows

Unlike a traditional window, a sliding window moves from left to right. Side-by-side casement sliders will conflict with each other since you can’t open both sides at the same time. The sashes of these types of windows do not allow you to fit a traditional window AC into it.

Because of this, a normal AC unit will leave a lot of space at the top which brings down the window AC unit’s efficiency or make you add other fitting work to cover up space. Also, most window AC units are too wide for typical casement windows.

Sliding windows come in standard sizes. So, do remember to measure the size of your window before you purchase an AC unit. The size of the air conditioner will also influence the power outlet. Larger casement air conditioners will need an independent 230-volt circuit and not the normal household 110-volt.

A casement AC performs best when its rear side is shaded from the sun. So, the best choice is to install the window air conditioner in a window where there is some shade – a tree, overhang, or even plants or shrubs can help, as long as they aren’t too close.

A metal frame is also installed to the sliding window to support the AC unit. This not only helps protect the window frame but also provides extra support to the AC unit itself, preventing it from putting a lot of weight on the sill and window jambs.

Basics of Cooling Potential

Each air conditioning unit has the potential to cool a space down based on its BTU rating. The BTU essentially indicates the amount of heat that the air conditioner can remove from a room. The larger the BTU rating, the larger the room that the air conditioner can cool.

A casement window air conditioner can come with a maximum of 12,000 BTU. That window air conditioning unit size can comfortably cool a room that’s slightly over 500 sq ft. If you have sliding windows and are looking for an AC for a larger space, we will recommend for you to consider a central air conditioning system.

However, you will also need to consider a few other aspects apart from the room size when measuring BTUs. The height of the ceiling, the use, the floor plan of the house, as well as the direction of the sunlight are some factors that will come into play when considering the size of the AC unit to buy.

Adding Security

Once you’ve found an efficient cooling option to cool your room with a sliding window, you might still be concerned about security, since it is not easier to pry open the window or break it. To help prevent anyone from sliding the window open and popping out the AC, you can cut a piece of wooden dowel such as a broom handle to block your window. Simply wedge it on the opposite side between the window jamb and the frame and intruders won’t be able to slide your window open.

Some windows may offer locks for different positions. You could also look for special casement window lock units at your local hardware store. Another security measure is to secure the top mounting rail into the window sash with its screws. This will also provide your unit with more stability.

The accordion panel on the AC might also pose a weakness. So, be sure to fasten it in place. A more extreme measure would be to install a grill made to go over the section. The next step would be for you to install a stick-on type window alarm. While being a good way to know when you’re facing a burglar, their visibility can also be a great deterrent to any intruders.

Life Hacks

Purchasing casement air conditioners could be an expensive proposition, especially if you just happen to move into a new house or apartment thinking that your old window AC would work. There are actually many hacks online that you can use to make a traditional unit work. Some online resources provide detailed instruction manuals and guides that will help you fit a traditional, horizontal AC in a sliding window. But it’s often necessary for you to hire a carpenter to create the right sized frame for your window. You may also need an electrician as well, depending on where your outlets are located and whether your AC is 120 or 220 volt.

Though it’s possible and a safe option if done by a competent installer, we don’t find this a preferred method. You may void your warranty because the unit is supposed to have a definite “top”. And if not done correctly, it could lead to electrical hazards, poor ventilation, or poor drainage.


Casement air conditioners are often designed to meet the very specific needs of sliding windows by addressing special challenges of the window size and shape, so we definitely recommend using this type of unit where needed and trust that it will serve you well and faithfully.

The ease of installation can vary with each AC, but many models are DIY. If you’re still wary of the installation, you can always consult a carpenter or electrician for help where needed. There’s no reason to suffer in the heat just because your window type – casement AC are both good to look at and highly functional. We hope today’s buying guide has given you sufficient information on the best casement air conditioner to keep your home cool and comfy this summer.

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