5 Best Casement/Vertical AC Units For Sliding Windows (2021)

Homeowners with casement windows have quite a struggle finding casement window air conditioners. Can you put an air conditioner in a casement window? Of course, you can.

Casement window air conditioners are narrow AC units. While standard window units for double-hung windows are wide and short, the casement AC units are narrow and tall.

To install a casement window AC, you need a minimum window width of at least 15 1/2 inches; do measure the window length to be sure you can indeed install a casement air conditioner. For installation, you will require a special vertical AC kit that usually comes with the unit.

Here is how placing the casement window AC looks in theory:

window air conditioner for casement and vertical windows
Casement or sliding window AC units are high and narrow. They are usually 15″ wide and about 21″ high.

There are few manufacturers that offer vertical window air conditioners. Frigidaire, Koldfront, and PerfectAire create the overall best ones. #1 10,000 BTU Frigidaire FFRS1022R1 and #2 8,000 BTU Koldfront CAC8000W are generally considered the best two vertical window air conditioners currently on the market.

To help you out with picking the AC for your casement window, LearnMetrics has prepared a list of the best casement window air conditioner. You can skip to the list here:

Skip To Best Casement/Vertical AC Units here

To adequately familiarize yourself with these vertical air conditioners for crank windows (also used as sliding window air conditioners), let look at what specifications you should look for to pick the best unit. Before we look at the specs preferences, let’s clear up the terminology about the casement AC unit:

Casement vs Vertical vs Slider vs Sliding Window Air Conditioners (Terminology Explained)

If you have a narrow window or a sliding window, it’s only natural that you won’t look for standard window units. You really have to find an air conditioner that will fit into the casement or sliding window.

There is no uniform term for these narrow AC units. Several terms are in use – and they all mean the same type of window air conditioner. To not get confused when checking these units, let’s look at the various names that are used to describe these AC units:

  • Casement window air conditioner”. Most commonly used phrase for an air conditioner that fits a casement window.
  • Vertical window air conditioner”. A term used to describe window AC units that fit vertical windows; ie. vertical AC units.
  • Sliding window air conditioner”. Air conditioners that fit a sliding window; you can install a sliding window air conditioner, and slide the window as close to the AC as possible, and use the kit to fill in the window gaps.
  • Slider window air conditioner”. Pretty much the same idea as sliding window air conditioners; sliding windows are generally referred to as “slider windows”. Hence the term “slider window AC units”.
  • “Air condition for crank window”.
  • “Thin or thinnest air conditioner”. Basically, just an AC with the highest ratio between height and width; thinnest AC.

In short:

“Casement” = “Vertical” = “Sliding” = “Slider”

All these terms are used interchangeably for the same type of window air conditioner.

Example: You can install a casement window air conditioner in a sliding door. You can also install a slider window air conditioner in a vertical casement window.

Now that we understand the terminology, let’s look at 5 most important specifications to check before you buy a vertical slider air conditioner:

5 Key Factors To Look For In Slider Window Air Conditioners

Due to window width restraints, sliding window vertical air conditioners have quite a few common properties. The most noticeable one is this:

They are narrow and tall. Casement window ACs width is about 14″ to 15″. The height dimension can be anywhere between 20″ and 30″, depending on the size (cooling capacity) of the unit.

Let’s quickly go over the 5 most important factors to choose the exactly right air conditioner for your casement or sliding window:

Cooling Capacity (Measured In BTU/hr)

The function of casement window AC (and any other AC) is to deliver a cooling effect. The cooling effect is measured in British Thermal Units or BTU.

Standard double-hand window ACs produce anywhere from 6,000 BTU to 15,000 BTU or even more.

Slider window air conditioners have a narrower cooling capacity. In practice, you will only find 8,000 BTU or 10,000 BTU casement window air conditioners.

10,000 BTU window AC units for crank windows or slider windows are by far the most prevalent due to a very simple reason:

Pretty much everybody is looking for a 10,000 BTU casement window AC unit. It’s the golden-standard capacity and by far the most sought-after vertical AC unit capacity.

Recommended Coverage Area (Based On BTU)

Based on the cooling effect (BTU), we can calculate how large a space that particular casement air conditioner can cool down. This is known as the recommended coverage area for the casement type of window AC unit.

For environmentally-friendly usage, the EPA recommends that the AC cooling effect to cool down 1 sq ft should be 20.

Example: If you’re looking to cool down a 500 sq ft area, you should look for a 500 sq ft * 20 = 10,000 BTU slider window air conditioner.

Of course, that’s the absolute lower limit. In practice, producers who calculate the recommended coverage area recommend 10,000 BTU air conditioners for up to 450 sq ft.

Example: Frigidaire FFRS1022R1 is generally considered the best casement window air conditioner. It has a 10,000 BTU cooling capacity and it will adequately cool down spaces up to 450 sq ft; 500 sq ft is a bit too big space.

What if you have a 300 sq ft place to cool down; should you still use the Frigidaire unit?

Yes, you can, just run it on a lower fan speed setting. An even better option is to choose a smaller 8,000 BTU casement window air conditioner. The best one – Koldfront CAC8000W – has an 8,000 BTU cooling capacity, superb 11 EER rating energy efficiency, and can cool down spaces up to 300 sq ft.

EER Rating (Energy-Efficiency, Important For Long-Term Electricity Savings)

Vertical window air conditioners should be energy-efficient. If they are, you will likely pay $500 less for energy over the next 10 years. If they are not, you will likely pay $500 more for electricity in the next 10 years.

Energy-efficiency is measured by the EER rating. EER stands for Energy-Efficiency Ratio and is calculated by diving the cooling effect (in BTU) by maximum energy-input (wattage).

Example: 10,000 BTU powered by 1000 W has an EER rating = 10,000 BTU / 1000 W = 10.

The higher the EER rating, the more energy-efficient a vertical window air conditioner you have, and you’ll pay less in electricity costs.

Any casement air conditioner with an EER rating of 10 is considered energy efficient. You can find EER 8 and 9 rated sliding window air conditioners as well.

If you check the comparison table below, you will see that all the best casement window air conditioners have superb energy-efficiency as well. 10,000 BTU units have a 10.4 EER rating, for example.

The compact Koldfront CAC8000W is the most energy-efficient vertical air conditioner with an 11 EER rating.

most energy efficient casement air conditioner with energyguide
EnergyGuide label of the Koldfront CAC8000W; the most energy-efficient vertical air conditioner.

Minimal Window Width And Height (Important For Fitting In The Window)

The whole point of air conditioners that fit into casement windows is that they are narrow. It only makes sense: a narrow AC unit to fit a narrow window.

Standard window air conditioners require the minimal window width to be at least 20″ or even 25″. Of course, the vertical casement slider windows tend to be 20″ or narrower.

That’s why all casement window air conditioners have a width less than 15″.

Here is where you have to be careful:

Despite casement window units measuring less than 15″ in width, that does not account for the width of the crank window AC installation kit. That can add an additional inch to the total width of the slider window AC unit.

All producers will give you the minimum window width in the specification sheet. All top casement window air conditioners have a min. window width of 15 1/2 inches. That’s the industry-standard dimension.

Here is how the installation kit for casement and sliding window ACs looks like:

casement window kit for air conditioner
Example of an installation kit that comes with pretty much all casement window AC units.

The height is less problematic; these are, after all, vertical windows. To double-check if the casement air conditioner will actually fit into your casement or slider window, make sure that your window’s height falls into the specified min. and max. window height interval.

Noise Levels (Quiet Casement Window AC Units Are Preferred)

Noise levels are quite straightforward; everybody prefers a quiet air conditioner. In fact, we made a separate list of the quietest double-hung window air conditioner here.

The slider window can be a bit louder than conventional units. To make sure the vertical unit has a super silent operation, check the noise levels. Everything below 60 dB is considered quite quiet.

Casement window air conditioners will have 2 decibel specs; for noise created on the inner side (facing the room) and for noise generated on the outer side (facing the outdoors).

The inner side noise levels are the ones that count; you will be in your room with the casement AC on.

It has to be said that many (but not all) slider window air conditioner producers specify the decibel levels. We consider the ones that don’t reveal that information less trustworthy.


With all that in mind, let’s look at the list of the highest-rated casement window air conditioners:

Best Casement Window AC Units (Useful For Vertical Windows)

  1. Frigidaire FFRS1022R1: Overall Best Casement Window Air Conditioner.
  2. Koldfront CAC8000W: Quietest 8,000 BTU Casement Window AC Unit With Superb Energy-Efficiency.
  3. PerfectAire 3PASC10000: Good 10,000 BTU Casement Window Air Conditioner.
  4. Keystone KSTSW10A: 10,000 BTU Vertical Window AC Unit.
  5. Global Industrial MWDUL-10CRN1-BCJ4: 10,000 BTU Slider Window AC Unit.
Casement Window AC: #1 Frigidaire FFRS1022R1 #2 Koldfront CAC8000W #3 PerfectAire 3PASC10000 #4 Keystone KSTSW10A #5 Global MWDUL-10CRN1
Photo:
Cooling Capacity: 10,000 BTU 8,000 BTU 10,000 BTU 10,000 BTU 10,000 BTU
Coverage Area: Up to 450 sq ft Up to 300 sq ft Up to 450 sq ft Up to 450 sq ft Up to 450 sq ft
EER Rating: 10.4 11.0 10.4 10.4 N/A
Min. Window Width: 15.5 inches 15.5 inches 15.5 inches 15.5 inches N/A
Max. Airflow: 323 CFM 235 CFM N/A N/A N/A
Noise Levels: 56/58/61 dB 51/53/55 dB 56/61 dB N/A N/A
Power, Voltage, Amps: 961W (115V, 10.0 A) 750W (115V, 6.5 A) 961W (115V, 8.5 A) 961W (115V, 8.5 A) N/A
Price: $$$$ $$$$ $$$$ $$$$ $$$$
Average Rating: 4.9 out of 5 stars 4.8 out of 5 stars 4.7 out of 5 stars 4.5 out of 5 stars 4.3 out of 5 stars
Availability: Check Price Check Price Check Price Check Price Check Price

1. Frigidaire FFRS1022R1 (Overall Best Casement Window Air Conditioner)

Frigidaire FFRS1022R1: Overall Best Casement Window Air Conditioner
Cooling Capacity: 10,000 BTU
Recommended Coverage Area: Up to 450 sq ft
EER Rating: 10.4
Min. Window Width: 15.5 inches
Max. Airflow: 323 CFM
Noise Levels: 56/58/61 dB
Power, Voltage, Amps: 961W (115V, 10.0 A)
Dimensions (HxWxD): 23.5″ x 14.5″ x 20.25″
Weight: 72 lbs
Price: $$$$
Rating: 4.9 out of 5 stars

Frigidaire is a very well-known big brand in the HVAC community. The Frigidaire FFRS1022R1 is the best air conditioner for casement or sliding windows. It has specifically designed as the most optimum AC for non-standard windows.

Frigidaire FFRS1022R1 is a 10,000 BTU casement window AC. It is installed on the window sill with a specially designed installation kit (you can the kit together with the unit). It has enough cooling capacity to adequately lower the temperature in areas up to 450 sq ft. On top of that, Frigidaire FFRS1022R1 also works as a dehumidifier; it will remove up to 3.4 pints of water every hour.

The energy efficiency is very good. The Frigidaire FFRS1022R1 has an EER rating of 10.4; far above the 9 EER rating average. This means it will use less electricity to generate the same amount of cooling effect; the electricity bills will be comparatively lower.

Here’s how you check if your casement window can accommodate the Frigidaire FFRS1022R1:

  • Minimum window width should be at least 15 1/2 inches. This is the thinnest air conditioner.
  • Minimum window height should be at least 21 1/2 inches.
  • Maximum window height should be 40 inches or less.

Frigidaire FFRS1022R1 is also fairly easy to use. It has multi-speed electronic controls, a 24h on/off timer, remote control, and all the important modes: Auto, Energy Saver, Sleep mode. The airflow can be directed in 4 different ways and it passes through a washable mesh filter (alert light will go red when you have to clean the filters).

All in all, the Frigidaire FFRS1022R1 was designed as the best casement window air conditioner. It has quite a good reputation for reliability and ease of use. Frigidaire FFRS1022R1 is the #1 rated vertical window air conditioner:

Frigidaire FFRS1022R1 Review

Pros
  • Made by Frigidaire; most well-recognized and reliable AC makes
  • Can reliably create 10,000 BTU of cooling effect for up to 450 sq ft
  • Easy to use: remote control with Auto, Energy Saver, Sleep models, and 4 airflow directions
  • Reliable and robust enough to easily last for 15 years
Cons
  • Noise levels on the highest fan speed settings is 61 dB; not loud but also not whisper quiet

2. Koldfront CAC8000W (Quietest 8,000 BTU Casement Window AC Unit)

Koldfront CAC8000W: Quietest 8,000 BTU Casement Window AC Unit
Cooling Capacity: 8,000 BTU
Recommended Coverage Area: Up to 350 sq ft
EER Rating: 11.0
Min. Window Width: 15.5 inches
Max. Airflow: 235 CFM
Noise Levels: 51/53/55 dB
Power, Voltage, Amps: 750W (115V, 6.5 A)
Dimensions (HxWxD): 23.5″ x 14.5″ x 20.88″
Weight: 75 lbs
Price: $$$$
Rating: 4.8 out of 5 stars

Koldfront CAC8000W is one of the best and most useful casement window air conditioners. It doesn’t matter if you have a casement window, a vertical one, or a slider window, the Koldfront CAC8000W can be installed in any of those, and what a unit it is:

Koldfront has created the best smaller 8,000 BTU vertical air conditioner with super specs. In fact, with an EER rating of 11, the Koldfront CAC8000W is the most energy-efficient casement air conditioner. According to the EnergyStar label, it will spend only $71 on electricity in the hottest 3 months in the summer. Other vertical AC units can spend more than $150 on electricity.

Apart from being extremely energy-efficient, the Koldfront CAC8000W is also the quietest slider window air conditioner. We said that anything below 60 dB is super silent. The Koldfront noise levels of 51/53/55 dB are completely below 55 dB. This is quite outstanding for a casement air conditioner.

There is one drawback, however:

The Koldfront CAC8000W can only be installed on crank windows that slide from left to right; it cannot be installed on windows that slide up or down. This is very important: you should have a horizontally sliding window to properly install the Koldfront CAC8000W.

All in all, the Koldfront CAC8000W is a superb smaller 8,000 BTU casement air conditioner best for smaller rooms up to 300 sq ft. It’s the quietest and most energy-efficient unit – a clear specs-by-specs winner – but it can only be installed in horizontally sliding windows:

Koldfront CAC8000W Review

Pros
  • Most energy efficient casement window AC unit with 11 EER rating ($71/season electricity expenditure only)
  • Quietest unit with the whole interval of noise levels below 55 dB (51/53/55 dB)
  • Will fit pretty much any window; casement, sliding, and so on as long as it slider horizontally
  • A reliable AC with superb reviews and track-record
Cons
  • Cannot be installed on a vertically sliding window (up and down)

3. PerfectAire 3PASC10000 (Good 10,000 BTU Casement Window AC Unit)

PerfectAire 3PASC10000: Good 10,000 BTU Casement Window Air Conditioner
Cooling Capacity: 10,000 BTU
Recommended Coverage Area: Up to 450 sq ft
EER Rating: 10.4
Min. Window Width: 15.5 inches
Max. Airflow: N/A
Noise Levels: 56/61 dB
Power, Voltage, Amps: 961W (115V, 8.5 A)
Dimensions (HxWxD): 23.5″ x 14.75″ x 21″
Weight: 72 lbs
Price: $$$$
Rating: 4.7 out of 5 stars

PerfectAire 3PASC10000 is one of the best casement air conditioners you can buy. Specs-wise it’s actually very close to #1 Frigidaire’s casement unit specs; that alone tells quite a lot.

It has a 10,000 BTU cooling effect. If you install it on the sliding casement window, you will be able to adequately cool down up to 450 sq ft. With every purchase of PerfectAire 3PASC10000, you’ll also get an installation kit for free.

To install it, your casement window has to be at least 15 1/2 inches wide. This is the thinnest air conditioner currently on the market. Vertically, the casement window min. height is 21 1/4 inches and the window max. height is 39 1/2 inches. Keep that in mind when you’re measuring your casement window.

PerfectAire 3PASC10000 is highly energy-efficient. It has a 10.4 EER rating, a standard number among the energy-efficient crank window AC units.

At its peak fan speed setting, it will drain 961W of power. Like all vertical window air-cons, it requires the standard 115V voltage.

In short, PerfectAire 3PASC10000 has superb specs, but the PerfectAire brand is not as well-recognized and a guarantee of reliability as Frigidaire:

PerfectAire 3PASC10000 Review

Pros
  • Superb specs: EER rating of 10.4
  • Easy installation (with included installation kit)
  • Good coverage (up to 450 sq ft) and 15 1/2 min. window width requirement
  • Affordable price
Cons
  • Peak noise level is above 60 dB
  • PerfectAire is not as well a known a brand as Frigidaire

4. Keystone KSTSW10A (10,000 BTU Vertical Window AC Unit)

Keystone KSTSW10A: 10,000 BTU Vertical Window AC Unit
Cooling Capacity: 10,000 BTU
Recommended Coverage Area: Up to 450 sq ft
EER Rating: 10.4
Min. Window Width: 15.5 inches
Max. Airflow: N/A
Noise Levels: N/A
Power, Voltage, Amps: 961W (115V, 8.5 A)
Dimensions (HxWxD): 23.5″ x 14.57″ x 20.87″
Weight: 35 lbs
Price: $$$$
Rating: 4.5 out of 5 stars

Keystone KSTSW10A is another good 10,000 BTU casement air conditioner. With 10,000 BTU, it can cool down rooms with casement windows that have up to 450 square footage.

It’s quite useful as far as the controls go. You have 3 fan speed settings and 4-way air directions. That means that you can adequately correlate the BTU output to your needs, and you can additionally direct the airflow to where it’s needed the most.

Keystone KSTSW10A can achieve a maximum EER rating of 10.4. It even has an Energy Saver mode that saves electricity and is more eco-friendly than the full turbo mode.

It can easily be installed in a horizontal slider of the casement window, as long as the width is more than 15 1/2 inches.

All in all, the Keystone KSTSW10A is a decent casement window AC unit that gives you a lot of control about the BTU output and the airflow direction:

Keystone KSTSW10A Review

Pros
  • High energy efficiency with 10.4 EER rating
  • Gives you freedom to regulate cooling output (3 speeds)
  • You can adequately direct the airflow (4 different ways)
  • Will fit any casement or horizontally sliding window that is wider than 15 1/2
  • Fair price
Cons
  • Noise levels are not specified
  • Keystone is not a big and well-recognized brand

5. Global Industrial MWDUL-10CRN1-BCJ4 (10,000 BTU Slider Window AC Unit)

Global Industrial MWDUL-10CRN1-BCJ4: 10,000 BTU Slider Window AC Unit
Cooling Capacity: 10,000 BTU
Recommended Coverage Area: Up to 450 sq ft
EER Rating: N/A
Min. Window Width: N/A
Max. Airflow: N/A
Noise Levels: N/A
Power, Voltage, Amps: N/A
Dimensions (HxWxD): 23.5″ x 14.63″ x 20.88″
Weight: 85 lbs
Price: $$$$
Rating: 4.3 out of 5 stars

Global Industrial MWDUL-10CRN1-BCJ4 is quite a mouthful. This is your basic 10,000 BTU air conditioner for slider windows that covers up to 450 sq ft.

The installation kit is included. When the AC unit is installed within the slider window, the total length of the AC itself is closer to 16″.

All the filters are easily removable and washable. You can the Auto restart and Sleep mode, even a 24 on/off function.

Truth be told, most of the specs about the Global Industrial MWDUL-10CRN1-BCJ4 are not known. This unit doesn’t seem to be special in any kind of way. It’s just a casement window AC that may be good but the reliability here is questionable:

Global Industrial MWDUL-10CRN1-BCJ4 Review

Pros
  • Decent 10,000 BTU casement window AC
  • Installation kit for sliding window is included
Cons
  • Many specifications are not known
  • Doesn’t really have anything out of the normal to offer
  • Global Industrial is an unknown brand

If you have any questions regarding these very niche casement window ACs, you can pose them in the comments below.

8 thoughts on “5 Best Casement/Vertical AC Units For Sliding Windows (2021)”

  1. I have an open LR, DR, Kitchen, hallway area that is roughly 23′ x 30.’ I need 14,000-15,000 BTU casement window air conditioner according to what I have read. I have a window on the side of the house where it would go, but all other windows are in the front, so getting two smaller units is problematic as it would be really ugly. It sounds like most casement window AC’s are up to 10,000 BTU’s. Does anyone make one in the size I need?

    Reply
    • Hello Deborah, you hit the nail right on the head; there is no 15,000 BTU casement window air conditioner. As you have correctly stated, all casement AC units are up to 10,000 BTU. It’s an engineering feat to create 15,000 BTU casement unit and up till now nobody has been able to create one.

      Reply
  2. I have a problem similar to the previous person (Debora) I also need 12000BTU but might be able to get away with 10K BTU if I can stand a little less coolness in my APT. The real problem I am encountering is size. I need 15 x 20, W x H. The dimensions in this article 15.5 x 23.

    Are there any units fitting the dimensions of my sliding casement window?

    Reply
    • Hello Leon, it is quite a common question. For 10,000 BTU units, the minimum width is 15.5 inches and the height is usually about 23 or 24 inches. It’s not ideal that these casement units are not made of other dimensions.

      Reply
    • Hello Tim, sadly there are no air conditioners with HEPA filters. The best you can do to reduce wildfire smoke is to get an air purifier with a high smoke CADR rating; you can check out some of the best air purifiers for wildfire smoke here.

      Basically, air conditioners use 5 different types of filters, and none of these are HEPA filters. You can have pre-filters, silver ion filters, activated carbon filters, electrostatic filters, and antimicrobial filters. Unfortunately, they don’t do much to reduce wildfire smoke which is especially challenging if you have an air conditioner with fresh air intake.

      Reply
  3. Why do these units have a width of 14.xx inches, but require a minimum of 15.5 inch window width?
    If they are 14.xx inches they should be able to fit into a 15 inch window right?

    Reply
    • Hello Kai, theoretically that’s absolutely true. However, in practice, you always have to allow about 1/2 inches on left and right of these thin window AC units. That’s how you ensure the unit doesn’t have direct contact with the window; if it would be in contact, the potential vibrations could damage your window and the unit itself.

      Reply

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