Best Air Conditioner for Vertical, Narrow, Casement/ Sliding Window [2021 Small Thin AC units Buying Guide & Review]

Did you know that it is not just our bodies that suffer from heat but our tempers also rise? So, how are you beating the sweltering summer heat, cooling the body and the tempers too? It could be time you considered selecting the best air conditioner for vertical, narrow casement or sliding window that will put out great cold air to beat that heat and the tempers…

In this guide;

Your best air conditioner for vertical, narrow casement or sliding window comparison table

The 13 step vertical sliding window AC unit buying guide

Best AC for vertical, narrow casement or sliding window review

  1. Frigidaire FFRS1022R1 10000 BTU 115-volt
  2. Frigidaire FFRS0822S1 8000 BTU Heavy-Duty
  3. Arctic King EWL08CRN1BJ9 15″ 8000 BTU 
  4. Perfect Aire 3PASC10000 10,000 BTU
  5. Kool King Slider 10000 BTU

Tips and precautions when operating your slim air conditioner for vertical, narrow casement or sliding window

Final thoughts on the  air conditioner for small window opening

Your best air conditioner for vertical, narrow casement or sliding window comparison table

Brand(click for pricing)BTU
Frigidaire FFRS1022R1 10000
Frigidaire FFRS0822S1 8000
King Kool Slider10000
Arctic King EWL08CRN1BJ9 15" 8000
Perfect Aire 3PASC10000 10000

Your 13 step buying guide for the Vertical window AC

So, what should you consider when choosing the best air conditioner for vertical, narrow casement or sliding window?

1. Thin  vertical air conditioner size/ Window size

Measure the size of the window where you intend to install the best air conditioner for vertical, narrow casement or sliding window. Read the selected room air conditioner size specifications and compare against the recommended window size.

2. The window location in the room

If your window is at the far end of a room, your best air conditioner for vertical, narrow casement or sliding window must have the ability to direct airflow to the desired direction.

If the room is long, select the tall  skinny window AC unit that has a “Power Thrust” or “Super Thrust” fan control. This feature pushes the cool air farther into the room.

3.The air conditioning unit BTU

The BTU (British Thermal Units) is a basic measure of thermal energy and determines the capacity of your side  sliding window AC unit. A bigger  window air  conditioning unit size and weight has more BTU capacity.

4.Your room size vs the slim vertical AC unit BTU

Measure your room length and width in feet. Multiply the length and width to get the square footage. The following table is a guide on the room size vs the required BTUs.

The best BTU capacity is not just a factor of room size.  You may need to adjust the capacity indicated on the table based on the other factors listed below;

 Room sizeBTUs Capacity Needed Per Hour
100 - 150 sq. ft.5,000 BTUs
150 - 250 sq. ft.6,000 BTUs
250 - 300 sq. ft.7,000 BTUs
300 - 350 sq. ft.8,000 BTUs
350 - 400 sq. ft.9,000 BTUs
400 - 450 sq. ft.10,000 BTUs
450 - 550 sq. ft.12,000 BTUs
550 - 700 sq. ft.14,000 BTUs
700 - 1,000 sq. ft.18,000 BTUs
1,000 - 1,200 sq. ft.21,000 BTUs
1,200 - 1,400 sq. ft.23,000 BTUs
1,400 - 1,500 sq. ft.23000 BTUs
1,500 - 2,000 sq. ft.30,000 BTUs
2,000 - 2,500 sq. ft.340000 BTUs

Apart from the room size, factor the following to get the right BTU capacity;

  • Increase the BTU if the ceiling height is more than the normal 8 feet
  • The above BTUs are designed for 2 people in the room. For every extra person, add 600 BTUs.
  • Should you be installing in the kitchen, increase by 4000 BTUs.
  • If your room is exposed to more sunlight, increase the BTU by 10%

5.How much heat is your room exposed to?

The amount of the heat your room receives will affect the required BTU capacity of your slim  window air conditioner.

The heat will be a factor of the number of windows and the direction they face. More windows mean that the room receives more sunlight especially those facing west and thus you require a higher BTU capacity narrow window AC unit.

The other factor is whether the room is under a shade. The room under a shade requires a less BTU capacity casement window AC unit than the one exposed to direct sunlight.

However, ensure that the airflow around the small vertical casement window air conditioning unit is not limited by the tree, shrub or other obstructions.

6.Your electrical power specifications

Know your home’s electrical system and ensure that your choice small window AC unit plug is compatible. Most homes can serve 115V  vertical window air conditioning units.

Those less than 230V may require a dedicated circuit. The units requiring 230V and above need special circuits and thus it is critical to confirm that the circuit can handle the additional power required to prevent circuit breaks.

7.The Energy Efficiency

Be on the look-out for energy star label and /or energy efficiency ratio (EER). The more efficient air conditioner for  small narrow  window will  have a higher EER.

You can save up to 10% on energy costs when you select  an air conditioner for casement window with an energy star certified  (source.). Moreover, you can are eligible to participate in the special energy bill savings program on offer by some local authorities.

8.Filter management

A dirty clogged filter affects the performance of the small window AC unit. Ensure that your choice of the air conditioner for sliding window is easy to access and clean. Also look out for the unit with a filter cleaning alert.

9.What is the dehumidification capability per hour?

When the room is humid, you need the tall  skinny window air conditioner  to cool and dehumidify at the same time.

10.Multiple cooling modes

Some vertical window air conditioning units come with multiple cooling modes for optimal efficiency. Look out for energy saving modes, fan mode, sleep mode or auto mode.

A sleep mode is where the slim, narrow double  hung window air conditioner increases the temperature gradually as you sleep. The increased temperature subsequently reducing pressure on the compressor and reduces the noise.


Make note of the noise levels the small casement window air conditioner for produces. Whereas some of the units are relatively quiet, others may get loud especially when on high setting.

Should you be light a sleeper, select a low noise thin vertical window air conditioning unit for the bedroom. Also, select a low noise unit for the office.


Choose the small casement window AC unit with a longer warranty.

13.Additional features

Be on the look-out for the best air conditioner for vertical, narrow casement or sliding window  that has features that make your life comfortable such as;

  • Setting the time when the narrow vertical window air conditioning unit kicks on and off in your absence through a programmable timer
  • Mechanical or electronic controls that are logical and easy to use. Electronic controls allow for more flexibility.
  • A remote control and possibly one that has a ‘follow me’ technology which enables you to set the temperature you want from the exact spot you are located in the room

Or those that improve the efficiency such as;

  • An electronic ionizer to assist the thin vertical air conditioner unit to more efficiently remove impurities from the air.
  • Venting options to recirculate room air, pull in air from outside or exhaust room air outside.
  • A long power cord.

The Best air conditioner for vertical, narrow casement or sliding window review

1.      Frigidaire FFRS1022R1 10000 BTU 115-volt: Air conditioner for vertical, narrow casement or sliding window with Full Function Remote Control


Air conditioner size

This  air conditioner for vertical window measures 20-1/4″ height, 14-1/5″ width and 23-1/2″ depth.

Window size

The slim window you plan to install the tall narrow window  AC unit should have a height between 21.5 inches and / 40 inches and a minimum window width of 15.5 inches.


This 10,000 BTU Frigidaire thin  vertical air conditioner  for casement window will  comfortably cool your 450 square feet room while dehumidifying up to 3.4 pints per hour


The tall casement window AC unit uses the standard 115V 60 HZ electrical outlet. With the  extra-long (6′ (6-1/2′) three-prong cord, you do not need to use an extension cord.

The thin, vertical, sliding window AC unit comes with an installation kit with SpaceWise® Adjustable Side Panels. Where necessary, extend these panels to fill in the space between the air conditioner and window frame.


To cool your room as desired, the air conditioner for  slim narrow  window features 3 fan speeds. You also get an Auto cool, Energy Saver mode and Sleep mode.

When you set to sleep mode, the temperature will gradually increase as you sleep and thus save you energy and running cost. Moreover, the 4-way air direction makes it easy to direct the cool air to whichever target.

Should you want to set the best vertical window AC unit to kick off or on at a particular time, make use of the inbuilt 24-hour programmable timer.

The timer allows you to preset the slim vertical AC unit to switch on and off in half-hour increments.

And to quickly cool or warm the room, make use of the cool/warm mode to speed up the fan.

Furthermore, your comfort is taken care of with the Effortless™ Temperature Control which maintains the preset temperature.

Make use of the remote control to adjust the setting from anywhere in the room.

The Effortless™ Restart feature makes it possible for the sliding or casement window air conditioner to auto-resume the previous settings when power is reinstated.


With this air conditioner for vertical window, you enjoy a much healthier environment courtesy of the Effortless™ Clean Filter   which reduces bacteria, airborne particles and other room odors.

Moreover this crank casement window AC unit Clean Filter Alert will notify you when the filter is due for a cleaning!

Energy efficiency

The narrow, slim window air conditioner has an Energy Efficiency Ratio (EER) of 10.4.

Additional features

You get to easily operate this narrow window AC unit with the Ready-Select® Controls at the touch of a button.

What about the electronic controls that allow you to set and read your desired temperatures at your own convenience?

Moreover, the slim vertical window air conditioning unit is UL/CUL (SA11087) Safety Certified.


  • Quickly cools the room
  • Easy operation via the electronic controls
  • Energy efficient
  • UL/CUL safety certification
  • Flexible air direction


  • A little heavier
  • Could do better with the packaging when delivering

Want to know if this slim vertical window air conditioner fits within  your budget?

>>>>>>Check  user reviews and today’s price on Amazon<<<<<<<<<<<

2.     Frigidaire FFRS0822S1 8000 BTU Heavy-Duty: Air Conditioner for Vertical, Narrow Casement or Sliding Window with Electronic Controls

Best air conditioner for vertical, narrow casement or sliding window...Frigidaire FFRS1022R1 10000 BTU

Slim  window air conditioner size

The slider AC unit measures 14-1/5″ width, 20-1/4″ height and 23-1/2″ depth.

Window size

The best window size to install this room air conditioner should be 15-1/2″ width and 21-1/2″ – 40″ height.

Room size

This tall vertical window AC unit cools a room up to 350 square feet.


This 115V air conditioning unit comes with a window mounting kit. Follow the installation manual to easily mount the unit in your vertical, narrow, sliding or casement window. The mounting kit also includes an adjustable panel to fill in the remaining space between the air conditioner and recommended window size.

Energy Efficiency
The  small casement/sliding window air conditioner has a 10.9 energy efficiency Ratio (EER).  Moreover, the AC unit is a low voltage start-up.


This 8,000 BTU Frigidaire air conditioner quickly cools your 350 square feet room. To adjust the room temperature to your desired temperature, use the multi-speed fan feature to the relevant choice from the three different fan speeds.

And, you can easily select the options using the Ready-select electronic controls. Get comfortable in any spot and use the full-function remote control to set and adjust the controls.

Moreover, with the 4-way air direction control, you can you to direct the cools air wherever you want it.

Should you desire to set the narrow vertical window air conditioner to switch on before you get home, use the 24-Hour On/Off timer.

Frigidaire FFRS0822S1 dehumidifies the 350 square feet room up to 3 pints per hour.


The narrow window air conditioner comes with an anti-bacterial, slide out and washable mesh filter. The filter also keeps the air clean as it removes room odors and other particles in the air.

Moreover, the 8000 BTU tall skinny window air  conditioner unit also comes with a Filter Check that signals when your filter is due for a cleaning.

Additional features

Frigidaire FFRS0822S1 has a Full function remote control which allows you to comfortably control the temperature and fan speed from anywhere in the room.

This casement window air conditioning unit is also UL listed.


  • Frigidaire FFRS0822S1l operates quietly and thus cooling the room without distracting your sleep.
  • Auto mode great at cooling the room


  • The remote control has no temperature sensor that would assist you to set the desired temperature for a specific location in the room
  • Could do with better packaging when shipping.

Want to know if this smallest vertical air conditioner fits within  your budget?

>>>Click  here to read  user reviews and check today’s price on Amazon<<<

3.   Perfect Aire 3PASC10000 10,000 BTU: Best Air Conditioner for Vertical, Narrow Casement or Sliding Window with multiple energy modes, “follow me” Remote and EER 10.4

AC unit for sliding window conditioner size

The Dimensions of this thin vertical window AC unit are 14 ¾” width, 21” height and 23 ½” depth.

Window size

The window width should be 15 ½” – 16 ¼’” and the height between 21 1/3” and 39 ½”.

Room size

This air conditioner for narrow sliding window cools spaces 400-450 Square Feet.


The package includes a window mounting kit for easy installation. Connect the NEMA 5-15P plug type to the 115V/ 60Hz power outlet.


Perfect Aire 3PASC10000 effortlessly cools your 400-450 square feet living room, bedroom, office etc. Use the electronic controls to set the 3 cooling and fan speeds (Low, medium or high). You can also set the slim  vertical AC unit to run on sleep, dry or energy saver modes.

When it gets humid, choose the “dry mode’ to dehumidify the room.

When it is not too warm but you need to circulate air, choose the fan mode.

The auto mode selects the best operating mode to achieve the desired temperature. The sleep mode conserves energy as it operates on a lower fan speed and gradually increases the temperature as you sleep and thus reducing the pressure on the compressor.

Make use of the full function remote control to adjust the above settings from any corner of the room.  Also, make a note to select the “follow me” feature and consequently the remote turns into a thermostat monitoring the specific location temperature. You can then set the temperature to the one you desire at the point where you are located.

To ensure that your room cools evenly, the sliding window AC unit comes with full range 4-way air direction.

The room humidifying unit also has an auto restart function in case of power loss.


The vertical narrow window air conditioner comes with a slide out front mounted filter access which is easy to clean. The slim vertical  AC unit also has a clean filter indicator to alert you when the filter is due for a cleaning.

Energy efficiency

Perfect Aire 3PASC10000 is energy efficient with an energy efficiency rating (EER) of 10.4

Additional features

Perfect Aire 3PASC10000 is UL listed.

What about eco-friendly refrigerant…

Add the 1- year warranty.

And, the LED display which makes it easy to read temperature settings and notifications


  • Follow me remote allows you to set the temperature at the exact spot you are at.
  • Additional fan only and dry operating modes
  • The Digital display
  • Great customer service


  • Some users find it a little noisy

Want to know if this tall skinny vertical air Conditioner unit  for  window fits within  your budget?

>>>>>>Check  user reviews and today’s price on Amazon<<<<<<<

4.Arctic King EWL08CRN1BJ9 15″ 8000 BTU Air Conditioner for Vertical, Narrow Casement or Sliding Window with Energy Star Rating

 Air conditioner size

The slim  vertical window AC unit has a 14.25″ width, 21″ and 23.5″ depth.

Room size

350 square feet


You easily install Arctic King EWL08CRN1BJ9 and connect to 115 Volts Amps, 15 Amps, 60HZ power outlet.


The 8,000 BTU Cooling Capacity air conditioner for vertical window will cool your 350 square feet room quickly. To achieve your desired room temperature, set the electronic controls to the respective 3 fan/cooling speeds (cool, fan, auto).

You can set the tall  skinny window air conditioner on Sleep Mode to save energy which enables the unit to increase temperature and thus reduce pressure on the compressor and thus save energy.

The LED wireless Remote control with “Follow Me” technology allows you control the settings to your convenience.

For even room cooling, make use of the adjustable 3-way air directions.


Clean air is vital and the air filter in this vertical narrow window air conditioning unit is washable. You even get reminded when the filter is due for a  cleaning!

Energy Efficiency

Since this air conditioner for narrow window is Energy Star Rated and has a 10.9 EER, it then follows that it will effectively utilize every watt. Set it to sleep mode which auto adjusts the temperature and save more energy.

Additional features

  • 24-hour energy saving timer  allows you to start/stop the tall  skinny window AC unit as desired
  • A one year Warranty on parts /labor
  • Thermostat


  • Efficiently cools the space
  • You set when you want the casement slider Window AC unit to start or shut down
  • Convenient control of settings via the follow me remote control


  • Sliding panels could be longer

5.     Kool King Slider 10000 BTU: Best Air Conditioner for vertical, narrow casement or sliding window (Best budget)

Air conditioner size

14.6 x 23.5 x 20.9 inches

The AC unit is 14.6 inches wide and 20.9 inches high and 23.5 deep.

Room size

This 10000 BTU slider window air conditioner will efficiently cool your 450 square feet room


Us the support bracket that attaches to the outside of the window to easily to install this vertical air  conditioner window unit and connect to a 115V power source.

To fill in the space between the air conditioner and window frame, the AC unit comes with expandable side panels.


This 10,000 BTU quiet slider casement window AC unit has 3 fan and cooling speeds.  Make use of the sleep mode function to save energy. With this unit, the controls are electronic with LED display.

You conveniently control the settings using the full-featured remote control with memory and ‘follow me’ technology.

Should you want to set the narrow small vertical air conditioning unit to switch on at a particular time, use the 24-hour On/Off Timer.

For even air distribution, Kool King Slider Air Conditioner comes with 4-way adjustable air direction.

The window AC unit also auto restarts.

Energy efficiency

Kool King Slider Air Conditioner is Energy star compliant and an Energy Efficiency Rating of 10.8


  • Highly efficient
  • Best budget narrow casement window AC
  • Relatively quiet operation


  • Some people have an issue with the listed 2 months shipping but some reviewers have received the AC unit in less than 2 weeks.

pointing finger 1 Best Air Conditioners

Want to  know if this sliding glass window air conditioner fits within your budget?

>>>>>>>>>Click  here to check user  reviews and latest price on Amazon<<<<<<

Tips and precautions when operating your best air conditioner for vertical, narrow casement or sliding window

Immediately Inspect

Inspect the best air conditioner for  thin, vertical, narrow casement or sliding glass window AC unit upon receipt for damages, defects or missing parts. Should you note anything unusual, immediate action allows you to take advantage of the seller’s / manufacturer’s return policy.

Make the right choice of window

A centrally located window works best. However, should the window on the far end of the room, make use of the tall  skinny window air conditioner vents to direct the cold air to flow to the rest of the room. However, ensure that the cold air is directed to the center of the room for uniform conditioning.


  1. The back vents of  your  slim  window air  conditioner  may cut your fingers. To prevent this occurrence, wear a strong pair of leather gloves to wear when unpacking and moving the best air conditioner for horizontal sliding window.
  2. As mentioned in the buying guide, ensure you are connecting to a suitable electrical system
  3. Read and understand the user manual and follow the manufacturer’s instructions to correctly install and secure the air conditioner for vertical window. Get professional help where necessary.
  4. Sometimes, you may find that the expandable side panels  of  the mini compact AC do not quite cover the remaining space. Some users have made do with construction Styrofoam / thick Insulating foam board to cover the gaps.
  5. Avoid sharing the power outlet with other appliances.
  6. Keep the carton in good order. You will need it to store the horizontal sliding window AC unit during winter.
  7. Should you notice the window vibrating after installation, the unit may not properly in place.
  8. If the narrow window air conditioning unit is not correctly tilted to the outside, you may notice water dripping in the room. Proper tilting is also critical as you do not want stagnant water in the unit and creating a perfect environment to grow mold and other organisms.


  1. Make sure the side protective cover is in place when operating the best air conditioner for vertical, narrow, casement or sliding window.
  2. Avoid operating the  ultra compact AC in wet spaces such as bathrooms or laundry
  3. To save on cost, maintain the set cooling mode and increase fan speed to get a feel of the cooler air.
  4. Keep the room well ventilated especially if stoves are in use.
  5. Clear any obstacles around air inlets and outlets
  6. Some users indicate that a ceiling fan may assist to distribute cold air from the AC  for  small window opening to cool rooms that are a little bigger than manufacturer recommendations.
  7. Avoid directing airflow to indoor plants or pets
  8. Take care of the power cord. Avoid placing the cord near flammable substances. Also, take care not to place heavy objects on it. Keep inspecting for damages and replace only with the manufacturer recommended option.
  9. When necessary, defrost the cold coil by running the fan mode for some time.
  10. The water draining from the air conditioner for sliding glass windows is contaminated and thus not fit for consumption
  11. For better performance, consider operating the other heat producing machines during the cool hours.
  12. Hire a professional when necessary
  13. Properly ground the best air conditioner for vertical, narrow casement or sliding window
  14. Every so often, inspect the external bracket and ensure that it is in good order to prevent the AC for  narrow window from falling.


Before you start cleaning, switch off power and circuit breaker.  Avoid using water as it may degrade insulation or leak into the machine. In case water leaks into your crank casement window air conditioner, switch off and get professional help.

Filters management

For those filters that need replacement, please follow the user manual instructions. However, most are replaced every 1-2 months. The frequency of replacement or cleaning may be influenced by the frequency of use, dust, fur-bearing pets in the home etc.

Follow the manufacturer’s instructions on filter cleaning. Cleaning of clogged, dirty filters is necessary as trapped particles may build up causing accumulation of frost on cooling coils. A clean filter may reduce the energy consumption of your narrow air conditioner for  vertical window  by 5-15% (source).

Dust your best vertical, narrow casement or slider window air conditioner with an oil-free or damp (water and mild detergent) cloth. Make sure you wring out any excess water to prevent leakages into the sliding  glass  window AC unit. Note that harsh cleaners, wax or polish are not to be used when cleaning the small window AC unit.

The evaporator and condenser coils

Whereas a clean filter is a great plus for the coil, it will still get dirty /clogged with time and thus reduce its efficiency to absorb heat. Keep the area around the condenser debris-free and also give the coils an annual clean up.

Drain channels

Keep the vertical sliding  window  AC clean. The website recommends passing a stiff wire through the drain channels.


To prevent fires, avoid using extension cables. If the best air conditioner for vertical, narrow casement or sliding window also has a heater, place it 2 feet away from combustible materials.

Do not leave open spaces to prevent break-ins. Cover gaps above or beside the slider casement window air conditioner.

Screw the narrow thin AC on the window to secure it further.

Also, avoid using gasoline or other flammable substances near the vertical window air conditioner.

Operating environment

Keep the spaces as cool as possible.  Insulate the rooms by covering the windows with plastic.

When the temperature is higher than 90 F, close window treatments such as blinds or curtains to reduce the amount of heat the room is receiving

Where possible have the room under a shade while also ensuring that no bushes or other items interfere with the AC operation.

Storage during winter

You may need to store the air conditioner for casement window during winter. Follow removal instructions and put your slim window air conditioner back to the original carton or cover with plastic to prevent dust/debris.

New season use

Inspect the small vertical air  conditioner window unit as well as the side panels to ensure that it is in good condition. Sometimes moisture may affect the panels.

Final thoughts on the best air conditioner for vertical, narrow casement or sliding window

When your window happens to be vertical or narrow, make use of the above buying guide for the best air conditioner for vertical, narrow casement or sliding window. From the listed units choose your best slim window AC unit and then follow the tips and precautions for maximum service.

All the best as you cool the temperature, cool the body and cool the tempers.

Happy cooling!

Could  you  be searching  for  something  to  gift  the  women in  your  life? Click  here for women’s gift  ideas.

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Could you be on the look-out for the best humidifier for sinus problems, allergies or asthma? Click here

Does noise disturb  your sleep? Click here for the  quietest portable air conditioners…

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Vicky Geem

Hi there, I'm Vicky!- an ardent reader, researcher and writer. And I love breathing in cool, clean, healthy air. No wonder the interest in information and products that cool, heat, moisturize or purify the air in our living spaces. At, I share this information with you in a way that helps you make better and wiser decisions. When I’m not reading, researching or writing, you are most likely to find me enjoying the cleaner air outdoors. Or minding what I eat as I tend to my kitchen garden, picking some and ... meet you in the kitchen! Or contact me on email  or facebook/vickygeem

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