The standard home window opens vertically, which is why so many window AC units are compatible with only vertical-sliding windows. But what if your home has windows that slide open and closed from side to side? The good news is that this doesn’t completely rule out the option for a window AC unit; there are plenty of sliding window ACs, also called casement AC units, to choose from.
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 cranks outwards. This guide will provide you with everything you need to know about sliding window air conditioners, covering everything from installation steps to the top sliding ACs on the market. So try not to let your sliding windows stop you from staying cool in the summer months.
Just like all window ACs, a casement AC is meant to be installed within a window space. After it has been secured into place, the first step of the air-cooling process is to get the air within the room moving. It does this by kicking on a blower and then activating a compressor.
As the compressor gets going, there is a cooling coil that begins to drop in temperature. Air from the room is pulled in by the blower, and it first moves through an air filter that removes all the unwanted dust and particles. The air then passes through the cooling coil, dropping in temperature before being blown back out into the room.
The only real difference between a casement (sliding) AC and the traditional portable window AC unit is the method for installation. These units are vertically structured to accommodate the horizontally-sliding windows. Installation is a bit trickier with this type of window AC – we’ll talk about the specific steps later on.
Horizontal vs. Vertical Sliding Window ACs
Shopping for a small AC unit for a window that opens up and down is fairly easy since most are intended for vertically-sliding windows. These are much easier to install since they essentially just rest in place and don’t require as much support. They are shaped like a horizontal rectangle, but come in all sizes depending on the size of the room you’re trying to cool – and of course, the size of the window.
For windows that slide horizontally, you’ll want to purchase a vertically oriented window AC. These are taller and skinnier than the traditional window AC unit. The main thing to remember is that there is no standard size for casement ACs. For this type of window, you must take measurements beforehand to size your new AC unit properly.
How To Find a Quality Air Conditioner for a Sliding Window
Cooling Power Vs. Area Coverage
You can’t expect to adequately cool a large space with a tiny AC unit. On the flip side, there’s no need for a massive casement AC if you’re cooling a room that is just 100 square feet in size. Properly sizing your AC doesn’t need to be a guessing game, and in fact, it shouldn’t be.
Consumer Reports says that “window air conditioners typically have a cooling capacity ranging from 5,000 to 12,500 British thermal units (BTU). As a rule of thumb, an air conditioner needs 20 BTU for each square foot of living space.”
So for a 200 square foot room, plan on purchasing a 4,000-BTU AC.
Size & Weight
Try not to let the compact size fool you; window ACs are a lot heavier than they look. Generally speaking, the higher the BTU, the greater the size and weight. When it comes to size, you must take measurements of the window so that the installation doesn’t lead to any unpleasant surprises. Be sure to take measurements for both width and height.
If you choose an AC unit that is greater than 8,000 BTU, plan on the installation being a 2-person job. If that’s not an option, opt for a unit that has a lower BTU rating, or choose two smaller units that are lighter in weight. Considering weight and size is not only about selecting a unit that the window frame can handle, but also one that you can handle.
Placement of your new AC unit should always be on your mind during the shopping process. Location within the home is a huge determining factor for the specific model you buy. For example, if you’re trying to cool down a room on the second story that is hit with direct sunlight for most of the day, you’ll want to purchase a powerful unit with a high BTU rating.
One of the first steps in the air conditioning process is to filter the air. The AC takes air directly from the room, but before cooling it down, it first filters out dust and other unpleasantries, like allergens and bacteria. Some ACs come with an outstanding filtration system that even works to purify the air within your home, while others do not.
Choosing a model that effectively filters out contaminants can prevent health issues and breathing problems down the road. Some AC units come with reuseable and washable filters, but others will need to have their filters replaced when the time comes.
Another function that only the best sliding window air conditioners provide is dehumidification. In other words, they work to dehumidify the air and bring down the moisture levels within the home. The main advantage of dehumidification is that it maintains healthy humidity levels, which can help with:
- Improved air quality
- Mold prevention
- Elimination of dust mites
- Protection of the home’s structural integrity
- A more comfortable living space
The overall efficiency of an AC unit is measured by the EER, or energy efficiency ratio.
According to Energy.gov, the EER of room air conditioners “is 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.”
One of the best ways to decipher an efficient AC unit 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 just have one airflow setting. It is up to you to decide if multiple airspeeds are important; although it’s not necessarily essential, it’s an added perk. Multiple airspeeds mean that you’ll experience maximum comfort, no matter the weather conditions.
Choosing a sliding window AC with programmable timed cycles is another cool feature that maximizes the unit’s versatility. Programmability allows you to switch the AC off after you’ve gone to bed for the night, or turn it on just before you arrive home from work. It also adds to the machine’s efficiency since you can time it to turn off whenever the air conditioning isn’t necessary.
Noise is a huge factor, especially if you plan to install this AC in the bedroom window. The quietest window air conditioners have a decibel rating between 40 and 60. Windows units are partially inside the home as well as outside, so noise is dispersed in both directions. But even so, you should always read reviews of the best sliding window air conditioners to learn about each unit’s average noise level.
Ease of Installation & Maintenance
Installing a window AC unit is a DIY project that rarely requires the help of a professional. That being said, some units are easier to install than others. Casement air conditioners tend to be bulky and heavy, so choosing one with easy installation steps from the manufacturer is a must. You’ll also want to find one that is easy to maintain and won’t require constant servicing.
Even though window AC units are a much more affordable alternative to central AC, you don’t have to give up on the idea of reliable warranty coverage. Some manufacturers offer better warranty policies than others. The trick is not only to focus on the length of coverage time, but also look into the specific parts, pieces, and defects that are covered by the policy.
7 Sliding Window Air Conditioners Reviewed
1. Frigidaire FFRS1022R1
Our Top Pick
|Energy Efficiency||10.4 EER|
|Dimensions||23.5” x 14.2” x 20.2”|
|Coverage Area||450 sq. ft.|
The Frigidaire FFRS1022R1 is specifically designed for casement windows or sliding window installation. This is just one of the many reasons that we have ranked it as the best overall AC for sliding window. It’s a powerful 10,000 BTU AC that can cool a room up to 450 square feet. The FFRS1022R1 is extremely energy efficient with an EER of 10.4. Any AC with an EER of 10 or above is considered highly efficient.
Frigidaire users love the fact that the unit comes with several programmable modes, including Auto Cool, Energy Saver, and Sleep Mode. There are multiple airflow settings with 4-way air direction that can be controlled directly on the unit or from the included remote. There’s a 24-hr On/Off timer that allows you to control the exact times that the AC is operating.
Here’s what Frigidaire company has to say about the AC’s filtration system: “Our antibacterial filter reduces bacteria, room odors and other airborne particles for a healthier, more comfortable environment.”
In addition to producing cleaner air, the filter is 100% washable, and you’ll receive alerts when it’s time to check the filter.
Because the FFRS1022R1 has so many great features, a lot of homeowners are asking if this unit can be installed in a standard window. Sadly, the answer is no; it is only compatible with casement or horizontally-sliding windows, so you’ll have to look into a different Frigidaire model if your home has standard vertical windows.
- Multi-speed fan
- Effortless temperature control
- Remote control operation
- 24-hour On/Off timer
- Antibacterial filtration system
- Not suitable for standard windows
2. Frigidaire FFRS0822S1
Best Small AC for Sliding Window
|Energy Efficiency||10.8 EER|
|Dimensions||14.2” x 23.5” x 20.2”|
|Coverage Area||350 sq. ft.|
Let’s face it; not everyone needs a window AC unit that is as powerful as the 10,000 BTU Frigidaire. If that’s the case, you can downgrade to a lower BTU with the FFRS0822S1. It comes with all the same great Frigidaire features, but it is reduced from 10,000 BTU to 8,000. This makes it better suited for a room that is around 350 square feet in size.
The FFRS0822S1 has an EER rating of 10.8, which means that it is slightly more efficient than the previous Frigidaire casement unit. It is specially designed for casement or sliding windows, so don’t try to install it within a standard window frame. Similar to the last model, this one is capable of dehumidifying a room, removing up to 3 pints of water from the air per hour.
On the Frigidaire customer reviews page, one customer raves about the unit’s easy installation and quiet performance: “The window that I needed to install it in is not very wide and left me no choice but to purchase a narrow style unit. It was very easy to adapt and install in a double-hung window…Turned unit on and I was amazed how quiet the fan sounded on high speed.”
The full-function remote allows you to control the temperature and fan speed precisely, you can even set a timer from across the room. All in all, this is an excellent choice if you need a narrow unit that fits within a nontraditional window design. The only negativity has to do with improper packaging, but if your unit arrives damaged in any way, you’ll receive a replacement from the manufacturer.
- Dehumidification + filtration
- Easy installation
- NSF certifications
- Antibacterial filtration system
- Issues with improper packaging
3. Koldfront CAC8000W
Horizontal Sliding Window AC Only
|Energy Efficiency||11.0 EER|
|Dimensions||23.5” x 14.5” x 20.9”|
|Coverage Area||350 sq. ft.|
If your home has horizontal sliding windows, you’ll need a window air conditioner that is tall and narrow. The best horizontal sliding window air conditioner only is the Koldfront CAC8000W. Similar to the 8,000 BTU Frigidaire we just reviewed, this one has a room coverage area between 300 and 350 square feet. It’s the perfect sized AC unit for large bedrooms and living spaces.
This unit is designed to fit casement windows only, which means it won’t fit windows that slide up and down. There are a few things we love about this 75-lb unit, and the first is the easy to use control panel. There are clearly labeled buttons for several air setting modes, including cool mode, energy saver, fan only, and dry mode. There are also multiple settings for airspeeds (auto, high, medium, and low).
The remote control that comes with the CAC8000W works from up to 16 feet away. A further remote reach would be nice, but the fact that the unit has a remote control at all is a cool feature. Energy Star has approved this AC, so you can expect lower operating costs thanks to the amazing efficiency of the CAC8000W. It has an outstanding EER rating of 11.0.
The manufacturer says that “this window air conditioner meets strict requirements set by the U.S. Environmental Protection Agency to guarantee eco-friendly operation…The CAC8000W’s sleep mode will ensure you’re resting comfortably while helping save on costly energy bills. This function will adjust the temperature periodically by 2 degrees F before returning to the set temperature after six (6) hours.”
For something fuel-efficient that works with horizontal sliding windows, the Koldfront unit is a worthy contender.
- Digital display with multiple settings
- Energy saving
- Dehumidification function
- Easy installation
- Remote reaches only 16 feet
- No timer included
Complete Slider Window Air Conditioner Kit
|Energy Efficiency||10.4 EER|
|Dimensions||23.5” x 14.8” x 21”|
|Coverage Area||450 sq. ft.|
The PerfectAire slider air conditioner window kit is another 10,000 BTU unit that is capable of cooling a room size of 400-450 square feet. The temperature can be adjusted from 62 to 86 degrees Fahrenheit, and there are 3 speeds for both the cooling and fan modes. All of this can be controlled from the full-function remote that comes with built-in room temperature sensors, serving as a portable thermostat.
PerfectAire feels that this is truly the perfect solution for cooling a home that has slider windows. “Cooling areas up to 450 square feet, this unit fits like a glove in such architectural windows without having to resort to costly custom designs. Find your comfort zone with adjustable temperature settings guided by electronic controls, three fan speeds and full-range air direction control,” says PerfectAire.
There are four unique modes for cooling the room, including Auto, Sleep, Dry, and Energy Saver. The full-range air direction control allows you to maneuver the airflow in whatever direction feels best. The only negative aspect of the PA unit is that it’s a bit louder than other casement window units. This is the biggest complaint, so this might not be the best choice for you if you’re looking for a bedroom unit and you consider yourself a light sleeper.
- Expandable mounting kit included
- 3-speed cool/fan modes
- Follow Me remote control technology
- Easy cleaning filter
- Louder than average operation
- Not ideal for the bedroom
5. Frigidaire FFRS0833Q1
Top of the Range
|Energy Efficiency||10.8 EER|
|Dimensions||23.5” x 14.2” x 20.2”|
|Coverage Area||350 sq. ft.|
Yet another Frigidaire product to make our list of best sliding window air conditioners is the company’s FFRS0833Q1. We – and thousands of Frigidaire customers – consider this to be a top of the range window unit thanks to its appealing aesthetics and high-tech control panel. Similar to the other Frigidaires, this one was explicitly designed for casement windows, so anyone with standard windows at home is out of luck.
The 8,000 BTU operation makes this the ideal choice for rooms spanning 300 to 350 square feet. While it works to cool the room, the FFRS0833Q1 also works to dehumidify the air, removing up to 3 pints of water per hour. The Ready-Select electronic controls allow you to easily select from a series of cooling options with the touch of a button, or you can use the full-function remote to control temperature and fan speed from across the room.
One happy Frigidaire reviewer talks about his great experience with this unit: “It really saved the day! My house is not insulated whatsoever when it’s hot outside, it’s hotter, inside. We had such a hot, and humid summer. This Frigidaire A/C was a god-send!”
And just like all Frigidaire casement units, this one works to filter out harmful bacteria, particles, and odors from the air within your home. Unfortunately, the company is no longer manufacturing this model, but you can still purchase it from approved sellers on Amazon.
- Creates healthier breathing air
- Dehumidifies & filters
- Full-function remote
- Appealing aesthetics
- Ready-Select electronic controls
- No longer manufactured by Frigidaire
6. Honeywell MN10CESWW
Best Portable AC for Vertical Sliding Windows
|Energy Efficiency||9.0 EER|
|Dimensions||15.2” x 18.1” x 29.4”|
|Coverage Area||450 sq. ft.|
There is another option for homeowners with casement windows, and it doesn’t require installing a window AC unit. The alternative is to invest in one of the best portable air conditioners on the market, like the Honeywell MN10CESWW.
This is a standalone unit that doesn’t require window installation; you’ll just place it in the corner of the room, plug it in, attach the ready made kit (see right) and enjoy cool filtered air from Honeywell.
The MN10CESWW is a 10,000 BTU air conditioner with powerful airflow and quiet operation. Honeywell is a well-respected manufacturer of home air quality products, and this one is an all-time favorite.
It has a temperature range between 61 and 89 degrees Fahrenheit, a built-in dehumidifier to remove excess water from the air, and a 24-hour energy-saving timer with remote control included.
Honeywell says that “it features an environmentally friendly refrigerant, auto evaporation system, a reliable dehumidifying function as well as a traditional three-speed, fan-only function. The MN10CESWW is a convenient portable air conditioner that delivers optimum cooling, dehumidification and fresh ventilation.”
The only downside is that the EER rating of this unit is 9.0, which is significantly lower than the other sliding window air conditioners on this list.
The added perk of choosing a portable standalone air conditioner is that there is no installation whatsoever. The machine comes pre-assembled, so simply plug it in and start enjoying. The other perk is that you won’t have to worry about emptying the dehumidified water since the MN10CESWW has auto-evaporation functionality. The removable filter is washable, so it can be reused throughout the AC’s lifespan.
- Quiet operation
- Easy to maintain
- Easy to store
- Feather-Touch control panel
- Easy clean dust filter
- Low EER compared to others
- Short warranty period
7. LG LP0817WSR
Best Portable AC for Horizontal Sliding Windows
|Energy Efficiency||9.0 EER|
|Dimensions||23.7” x 18.7” x 16”|
|Coverage Area||200 sq. ft.|
Similar to the Honeywell we just reviewed, the LG LP0817WSR is another portable AC unit that requires no advanced window installation. Just like the majority of LG home appliance products, the LP0817WSR features a sleek design that fits well in any home.
With this portable AC, you won’t have to worry about an unappealing window unit protruding from your home. It can be conveniently placed in the corner of your bedroom or living space, and it won’t take away from the room’s aesthetics. It still does need to be vented and comes with a hose and kit that fits windows with fits widths and heights from 18″ to 50″.
This LG AC comes in a few different size options, including units for home spaces ranging from 200 to 500 square feet. The 8,000 BTU unit is perfect for bedrooms that measure 200 square feet, but if you’re looking for a unit that can cool a larger space, opt for the 10 or 12,000 BTU portable AC instead. No matter which size you choose, your LG portable AC will work to dehumidify the room and filter out any dust, bacteria, and odors from the air.
The thing we love most about this AC is its maximum usability display. LG says that it’s easy to “operate with LED display and simple selection control panel, up/down temperature adjustments, and fan speed selection, using the full-featured remote without leaving your bed, workspace, or couch.” It comes with a 24-hour On/Off timer, an auto-restart function for power outages, and an auto evaporating system.
The only downside of the LG is that the 8,000 BTU unit is not as capable of cooling a large space, especially when compared to the Frigidaire models. If you need to cool down a large area that is over 200 square feet, you’ll have to upgrade to a higher BTU unit, and these come with higher price tags.
- Sleek LG design
- Compact & lightweight
- No installation required
- Far-reaching remote control
- Simple selection control panel
- Less capable of cooling large space
Comparing Sliding Window & Other AC Types
|Type||Max Room Size||Most Common BTU||Dehumidifier
|Sliding Window||450 sq. ft.||8,000-10,000||Yes||$21 per month
|Fixed Window||450 sq. ft.||10,000||Yes||$29 per month
|Thru-The-Wall||550 sq. ft.||12,000||Yes||$38 per month
|Portable||350 sq. ft.||8,000||Yes||$21 per month
|Central AC||Whole House||36,000||No||$75+ per month (36,000 BTU)||$$$$|
Benefits of Slider ACs
Choosing a slider AC is the ideal choice for many, but some homeowners won’t benefit from this type of cooling unit. The main benefit is that it is compatible with casement and horizontally-sliding windows. Plus, a slider AC unit won’t break the bank as a central AC system will. Here are a few more benefits that come along with installing a slider AC unit:
- Since it’s not a permanent fixture, it’s easy to remove if ever necessary.
- Most modern sliding units are versatile with a wide selection of programmable features.
- The best sliding window air conditioners are efficient to run, especially those with the Energy Star label.
- Drainage is possible without the need for added plumbing.
Negatives of Slider ACs
Now that we’ve covered all the significant positive aspects of choosing a sliding AC unit, let’s talk about the negatives. There aren’t many, and most people will agree that the positives outweigh the negatives. The main drawback is that window units aren’t the most aesthetically pleasing method for cooling down the home. But this is true of all window AC units, not just sliding ones.
Another concern is the lack of home security once the unit has been installed. Many people worry about an intruder removing the AC unit from the window, leaving the house wide open for anyone to come in. This is, of course, a possibility with any window unit, but there are plenty of ways to prevent this.
Many windows lock in different positions, so this is your first option for adding security. If that doesn’t work, purchase a window locking unit at your local hardware store or online. If you’re still feeling worried about security, install a window alarm that will sound as soon as someone tampers with the window or sliding AC.
Determining the Right Size AC for Your Window
There are two main factors to consider when determining the right size AC for your window: window size and room size. You’ll first need to choose a unit based on the size of the window; even selecting one that is a quarter of an inch too large means that you’ll have to return the AC and start from scratch.
The second consideration is the size of the room. The larger the room, the more space there is to cool, so the more powerful your AC will need to be.
The window air conditioner buying guide by Lowe’s states that the BTU rating “indicates the amount of heat it can remove from a room. A higher number means more cooling power for a larger room.”
Most sliding window air conditioners range from 5,000 to 12,000 BTU. For rooms that have a square footage between 150 and 350, look for a window unit between 5,000 and 8,000 BTU. Rooms that are between 350 and 550 square feet require a more powerful AC unit, anywhere between 8,000 and 12,000 BTU.
Sliding Window AC Installation Steps
Installing your new sliding window AC can be completed as a DIY project within an hour or two. Installation is especially easy if you have a window that slides up and down. The first step is to open the window as wide as it will go. Then, carefully set the AC in place and slide down the window so that it makes contact with the top of the unit.
Using a set of shims (most manufacturers include these with the unit) ensures that the AC is leveled, but remember that it should be angled slightly downwards to promote drainage to the outside of the home. To secure it in place, use the included installation hardware and seal the window wherever needed. Finally, plug it in and start enjoying the cool breeze.
Installation of a casement AC unit in a horizontally-sliding window is similar, but there is just one major difference.
The Spruce says that installing a casement window air conditioner requires more support than a portable AC, so “you will begin by installing a wooden support base of your own making on the window sill, and then the metal manufacturer-supplied platform assembly on top of that support base.”
Care & Maintenance
The best way to keep your window AC running smoothly is to give it the love and care it needs. The most important maintenance step is to clean or replace the filter. Most filters can be removed and washed, but if the filter is in rough shape, you might want to replace it altogether.
Cleaning the coils is another important step, and the best time to do this is whenever you remove the filter. The coils are located right beneath the filter, and the easiest way to clean them is by using a vacuum brush attachment. This will remove any dust and debris that has gotten in the way of airflow.
Frequently Asked Questions
Is it safe to use extension cords to run sliding window air conditioners?
Hunker says that “window air conditioner should be installed close enough to an outlet to allow the cord to reach, but when you need immediate relief from the heat, you can use an extension cord for your new appliance. The one you choose must be heavy enough to handle the load, which for many air conditioners is around 12 amps.”
How do I determine which sliding window AC to get based on my apartment size?
The window AC you choose is based on a few things, but the main one is BTU vs. square feet. The BTU of the unit you choose should be directly related to the size of the room you’re trying to cool. The BTU rating of window units ranges from 5,000 to 12,000; a small 150 square foot room will do just fine with a 5,000 BTU room.
Do all portable air conditioners have to be vented out a window?
There are some types of portable air conditioners that serve as standalone units and do not need to be vented through a window. But when you purchase a window AC like the ones we covered in this list of best sliding window air conditioners reviewed, then yes, you will need to vent and drain them out of the window space.
Can I mount a standard AC on a sliding window?
Although it is not recommended, there are a few ways to get by with a standard AC on a sliding window. Instructables says that “if you already have some of these air conditioners or are attracted to them because their price tags are significantly lower than that of casement units, portable units, or central air, it is possible to make a frame to adapt them to sliding windows.”
Is the unit installed from the outside or inside? What holds the unit in place?
The unit will be installed from the inside of your home, and it is held in place by brackets and supports that are provided by the manufacturer. If you want to add additional support shims or brackets, you can do that, but never alter the actual AC during installation.
How can I fill in the gap left between the unit and the upper window frame?
Bob Vila provides some helpful insight for installing a window AC: “Once the upper pane is secured, there will be a gap between the two panes of the window. Fill that gap with the foam seal included with the unit. Cut the seal if necessary to fit your window, and then press it into the gap. This keeps drafts from outdoors out of the room.”
Do I need a professional HVAC technician to install a sliding window air conditioner?
No, you do not need to hire an HVAC professional to install your new sliding window AC. But “if you live in an apartment, condo complex, or a neighborhood with a homeowners’ association, check with management or the HOA board before investing in a unit. Some complexes don’t allow window ACs for aesthetic reasons.” This is very rarely the case, but it’s still a good idea to check beforehand.
Still searching for the perfect sliding window air conditioner to cool your home down? Very few casement AC units compare to the Frigidaire FFSR1022R1. This window AC comes with multiple program settings, an easy-to-use timer system, and a high EER rating. To top it all off, the Frigidaire filter is designed to reduce bacteria, odors, and airborne particles, so you’ll be breathing cleaner air while you stay cool.
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