Windows that slide horizontally, also known simply as sliding windows, casement windows, or slider windows, have long been a source of frustration and homeowners looking to cool their homes without having to install intrusive central air conditioning. 

There’s plenty of conditioners on the market for vertically sliding, double-hung windows, but manufacturers of air conditioners that fit into narrow, left-to-right sliding windows have for years been few and far between. The same is true for air conditioners that fit casement windows, which are sometimes called crank-out windows.

Fortunately, with increased demand for casement fitting AC, leading home appliance brands have responded by producing more models of slider window air conditioner for sliding windows, and I’m here to check out some of the most popular in 2021. 

You can trust my guidance, since it’s informed by over a decade of experience working in the Heating, Ventilation, and Air Conditioning (HVAC) industry. I’ve seen lots of families benefit from the home comfort that air conditioners can bring, and I want you to be the next person to benefit from my knowledge and expertise. 

Air Conditioner For Horizontally Sliding Window Buying Guide

Energy Efficiency Rating

How efficient an AC is at turning energy into cool air is an important consideration for many who are conscious of their carbon footprint and want an eco-friendly option. With a casement AC, this is measured by its Energy Efficiency Ratio (EER) rating. 

The best window AC’s have higher EER ratings, and you should look out for a rating of at least 10.0 if you want to save money off your energy bills in the long run. Window AC units usually have a higher energy efficiency than a portable air conditioner, though less so than central air conditioners.

If a unit has been awarded Energy Star certification, then it has met the strict criteria set by the US Environmental Protection Agency for reducing energy consumption. Look out for units with this award when you’re looking for your casement air conditioner! 

Cooling Capacity

Understanding the correct cooling capacity you need for your home is an important first step when shopping for your AC unit. A unit that’s too large will leave you uncomfortable and will also consume energy you don’t need to pay for! But go with a model that’s too small, and you won’t be able to adequately cool your room.

Cooling power is measured in British Thermal Units (BTUs). To calculate the BTU you’ll need for your room, measure its height and width, then multiply these dimensions together. So, for example, a 21.5 x 21.5 ft room will be 450 square feet. 

When looking at casement air conditioners, you’re a little more limited in the size of unit you can choose from than vertical window units. Currently, every casement window air conditioning unit comes with either 8,000 BTU or 10,000 BTU.

An 8000 BTU unit will be able to effectively cool a room of up to 350 sq ft, about the size of a home office or single bedroom. A 10000 BTU unit will quickly cool a room up to 450 square feet- that’s plenty for a double bedroom, living room, or dining area.  Anything beyond these sizes without a vertical window, and you’ll be better looking at other air conditioning options, such as central AC.

Remember, the BTU you need will also be influenced by direct sunlight in the room, the climate you reside in, and how well insulated the room is. You can use this BTU calculator which considers all these factors.

Unit Dimensions

Another size you’ll need to consider is the physical size of the unit. Window units are comparatively small, but it’s still important to check that you’re getting one that isn’t too big for the space you’re planning on installing it into. 

The casement and sliding window unit is the thinnest on the market, which also makes them some of the tallest. Most will need a minimum window height of 21.5 inches, and will not work in a window taller than 39.5 inches. 

They’re also notoriously heavy, and some weigh around 120 to 140 pounds! Check sure your window is big enough for installation, and enlist the help of an extra person to avoid putting your back out!

Air Conditioner For Horizontally Sliding Window Models

Frigidaire FFRS0822S1 8000 BTU 115v Window-Mounted Air Con

Frigidaire was around for the dawn of the modern AC as we know it, and the American company is well-established here in the US and known worldwide for its quality HVAC products. This particular model of 8,000 BTU window AC is one of the most popular on the US market today, and after running some tests it’s easy to see why. 

The unit has 8,000 BTU, which is plenty of cooling power for an office space or living room, and a super-quiet operation of around 40decibels makes it well-suited to bedroom installation too. It can also be used as a dehumidifier and removes around 3.4pints of moisture from the air per hour.

A full-function remote control provides a means of changing any setting that you would with direct electronic controls, without having to get out of bed or interrupt that Netflix binge! 

There are 3 different cooling speeds to choose from, altered by easily changing the fan speed, so you can lower the room temperature as quickly or gently as you prefer. And if you live in a hot climate and need a blast of cold, then the 4-way air direction control is a perfect feature for you.

It may not be the most energy-efficient model I’ve come across, with a low 10.8 EER rating, but then this is the case with most slider ACs. A useful Energy Saver mode conserves energy consumption when it isn’t needed to and does mitigate some of the issues.

I’ve also found that installation could be tricky if you don’t have any prior experience with a similar job, and the included instructions manual isn’t very clear either. While its narrow design means it’s great for thinner casement windows, it needs a minimum window opening height of 21.5inches, which is the tallest I’ve come across during my research for this review.

Aside from these relatively minor negatives, I can confidently recommend this model! It’s one of the best window air conditioners I’ve come across.

What We Like:

• Effectively and quickly cools spaces up to 350 square feet
• Variable fan speeds
• Remote control
• Especially great for narrow windows
• Quiet operation- perfect for bedrooms
• Four-way airflow control
• Dehumidifier mode removes 2.4pts of moisture per hour
• Energy Saver mode

What We Don’t Like:

• Not very easy to install without prior experience 
• Included instructions aren’t great
• No auto-restart

Frigidaire-FFRS1022R1-115-volt 10,000 BTU window/casement AC

This is the big brother of the Frigidaire FFRS0822s1, with all the same great features and an increased cooling capacity of 10,000 BTU for efficient cooling of spaces up to 450 sq ft. It will work effectively in a double bedroom, living space, or even a small studio apartment.

The Frigidaire FFRS1022r1 also boasts multi-speed electronic controls, a 24 hour on/off timer, and extra modes including auto cool, and sleep mode which makes it great for cooling large double bedrooms.

Things We Like:

• All the same great features of the Frigidaire FFRS0822s1, with extra cooling power!

Things We Don’t Like:

• Need a window frame minimum height of at least 21.5inches

Koldfront CAC8000W 8000 BTU 115V Casement/Slider AC

Koldfront has been at the forefront of electrical and domestic appliance manufacturing for small spaces since 1999. This unit is a great example of their expertise in this area and is designed for quiet operation in 350 sq ft bedrooms, small living spaces, or offices. 

It has plenty of useful extra features, including a sleep mode that lowers the fan speed during the evening as your indoors naturally cool down, a remote control, a three-speed fan, and an installation kit included that will provide a means of getting set up quickly. There’s also a dehumidification feature to reduce moisture levels.

The coveted Energy Star award is proudly emblazoned on the unit, so you know it’s one of the most efficient models around.

The warranty is a bit limited and only lasts 90 days, but since this unit is well-built (and heavy!), I’d recommend it if you’re looking to cool a smaller space but still have some nice extra features.

What We Like:

• Will effectively cool a room up to 350 square feet
• Easy to read digital display
• Also acts as a dehumidifier
• Sleep mode
• Three fan speeds
• Remote control
• Energy-efficient and Energy Star certified
• Installation kit included

What We Don’t Like:

• Not the best warranty- only lasts 90 days
• Heavy compared to other units
• No auto-restart

PerfectAire 10,000 BTU Casement AC

This unit from PerfectAire, a rising HVAC manufacturing company that’s been around since 2009, is engineered to handle the cooling of a space up to 450 sq ft.

Multiple airflow direction control targets especially warm areas of a room, and you can aim this at yourself for a refreshing blast of cool air on those especially scorching summer days! You can alter the airflow further by choosing one of three fan speeds.

A washable filter that can easily be taken out of a front-facing port means that maintenance is easy, so this is a unit to consider if longevity is your priority. There’s a full-function remote included, but aside from that, it’s a pretty basic unit that does what you’d expect at an affordable price. 

What We Like:

• Can cool a room up to 450 square feet
• Full-function remote control
• Choose from 3 different fan speeds
• Washable filter
• Four-way air direction control
• Powered by a standard 110-volt output

What We Don’t Like:

• No energy saver mode

Global Industrial Casement 10,000 BTU AC 115V

Global Industrial is a New York-based industrial and office supplies manufacturer, founded in 1949. They may not be as well-known for their air conditioning products as some of the other brands on this list, but I’ve still found this unit to be a decent option at an affordable price.

Built with 10,000 BTU of cooling power, this model can quickly cool a room of up to 450 square feet– for example, a medium-sized living room. 

One of the unique selling points of this model is the Follow Me program designed to provide efficient, on-the-go temperature control. If you leave a room with the remote in hand, the unit will detect this and adjust its temperature settings accordingly so you’re not consuming energy you don’t need to.

Four-way air direction control ensures you can cool down specific parts of a room more quickly, and sleep mode is perfect for the evenings when the unit will automatically and steadily reduce the fan speed, so it’s not too cold when it’s time for bed.

Unfortunately, this unit’s warranty is only valid when bought directly from Global Industrial, so if you buy from a third-party seller, you’ll need to contact the manufacturer separately to benefit from the 3-year limited parts warranty. 

I’ve also noticed some issues with the compressor when selecting a temperature above the minimum setting of  62℉, so this model isn’t ideal if you live in a milder climate and don’t always want maximum cooling power. Ultimately though, it’s priced less than most other 10000 BTU models and will probably suffice if you’re buying on a tighter budget.

What We Like:

• Can effectively cool in a room up to 450 square feet
• Four-way air direction control
• Multiple speed fan
• Full-function remote 
• Follow Me program designed to provide on-the-go control
• Budget-friendly price

What We Don’t Like:

• Warranty only valid when purchased directly from the manufacturer
• Compressor inefficient above minimum setting of 62℉
• Noisier than competing ACs

Horizontally Sliding Window Air Conditioners: Prices

Air conditioners for casement windows are a much more affordable option than installing central AC. However, their specific design means they’re also slightly more pricey than vertical units. I’ve compiled some of the price ranges you can expect to pay depending on the BTU cooling capacity, with the extra cost of accessories and installation included.

Who Can Install My Horizontally Sliding Window AC?

Most window AC units, including the sliding window AC and the casement window air conditioner, are designed for DIY installation. They’re a lot easier to install than conventional central AC units since they require no intrusive ductwork and just some very basic knowledge of electrical appliances.

However some window AC units are comparatively heavy, and you could need at least 2 people to carry out the heavy lifting required to lift the AC into the window frame. I’ve also found some brands don’t have very clear instructions on how to install their model, so you might need to look for some helpful how-to videos online.

If you are installing your window air conditioner upstairs, the packaged installation kit must be used correctly, to stop the unit from falling onto somebody below! If you’re unsure, it’s best to enlist the help of a licensed electrician or HVAC specialist, who will be able to safely and securely install your unit.

Horizontally Sliding Window Air Conditioners: Frequently Asked Questions

Can You Put A Window AC Unit In A Horizontal Sliding Window?

If you’re looking for a casement AC unit and you own a home with windows that open horizontally, you’ll require an air conditioning unit designed specifically for use with this type of window frame.

If you attempt to place a window AC horizontally by standing it on its side, you’re very likely to damage the components inside, especially the compressor which is the most expensive part of an air conditioner to replace. 

A casement window air conditioner is also suitable for use with a slider window unit. They’re affordable and easy to install, so don’t be tempted to fit a regular AC unit to your window- get the right window-mounted air conditioner for the job.

How Do You Use A Window Air Conditioner With A Horizontal Sliding Window?

A casement window air conditioner model, once properly installed, is easy to operate with very little maintenance required. Nearly every casement air conditioner runs off either a 110 volt or 240-volt standard mains outlet. There’s no need for complicated electrical wire tampering. 

Window air conditioners are designed to be able to run safely 24/7, so simply turn the unit on, select your desired setting using a remote control or by activating one of its extra features, and then enjoy your cool and comfortable room!

What Air Conditioner Should I Use For Large Horizontal Sliding Door Window?

You need to make sure that you purchase and install a window AC unit that’s specifically designed for sliding windows or casement windows. Any other type just won’t work and attempting to fix a vertical (or double-hung) type of AC to a slider window is likely to damage both the model and your windows!

There are a few good choices of slider window AC on the market today, and most are narrow enough and tall enough to be used with a large slider window frame of up to 40inches tall.

My Final Thoughts

Hopefully, I’ve helped you understand what you’re looking for from the best sliding window air conditioners. A sliding window air conditioner is perfect for bedrooms, offices, and living spaces between 350 square feet and 450 square feet. They provide a means of quickly cooling your chosen space quickly, quietly, and efficiently, without consuming power you don’t need to pay for.

While options are limited compared to other air conditioning options on the US market, there are now enough good quality units to choose from that you can find something that’s just what you’re looking for. Follow my guidance, and you’ll find the best sliding window AC for you and your home!