Written By
Josh Mitchell
Expert Reviewed By
Holly Curell
Last Updated On
August 9, 2024
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Over the years, I’ve helped countless customers fit their window ACs for home comfort, but not all windows are created equally.
Thankfully, horizontal sliding and casement window air conditioners (also called vertical air conditioners) are available for rooms without standard windows.
Below, I cover the best sliding and casement window air conditioners to help you effectively cool your space.
I’ve included some creative options as well – read on!
Quick Glance - My Recommendations
In This Article
Understanding Your Window and the AC Options Available
Vertical Windows
Vertical window ACs are the industry standard for window AC, and they are widely available in various sizes and with various features. These window ACs are best for:
- Standard Hung Windows:
These windows have two panels. The bottom panel slides up, and the top panel is fixed. Typically, these windows are at least 24” wide by 36” tall, and these are often found in older homes. - Double Hung Windows:
These are the most common type of windows in the US, with both panels able to slide up and down.
Horizontal/Casement Windows
These types of windows are less common, which means that window ACs made specifically for these windows are also less common.
For this reason, I often find that horizontal/casement window ACs are much more costly than their standard counterparts.
Also, it’s a bit confusing, but please note that even though these units are for windows that slide horizontally or outwards on hinges, they are sometimes labeled “vertical window ACs” because of their taller orientation.
- Horizontal Sliding Windows:
These window panels slide to the side. Sometimes one panel is fixed, and sometimes both window sash panels are able to slide horizontally. - Casement Windows:
These windows open out like a door on a hinge. They are often controlled by a crank that allows opening/closing, and are typically the most narrow type of window.
ACLAB Note:
With special window kits, it’s also possible to install a traditional portable AC like the SereneLife into various types of windows, which I’ll go into more detail on shortly.
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6 Best Air Conditioners For All Types Of Sliding Windows
Various window types and air conditioners are certainly not a match made in heaven.
These are some of the solutions I have installed, used and recommend for homeowners.
You can also check the out on my Amazon storefront sliding air conditioner list.
1. PerfectAire 3PASC10000 - Best Budget Option
4.5
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4.5
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4.5
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4.5
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Height
21"
Window Type
Vertical/Casement
SEER
13
Pros
- Low energy consumption
- Comes with full mounting kit
- Neat portable thermostat
- Can work with horizontal and vertical sliding windows
CONS
- Loud
- Packaging issues
Cooling always comes with a cost, but PerfectAire 3PASC10000 is a high energy efficiency AC which makes that pill less bitter to swallow.
The PerfectAire is both the most affordable horizontal sliding window AC on my list, and will offer the most long-term cost savings.
I recently installed this unit for a 400-square-foot backyard guest cottage, and it’s been perfect for the space. With 10,000 BTU of cooling power (just like the Frigidaire), it does a great job of keeping large spaces cool.
It’s rated for up to 450 square feet, but I think it could even take on slightly larger ones, similar to the Frigidaire model below.
I really appreciate that the PerfectAire ships with a complete installation kit, including accordion panels, a support bracket, a top rail, and even a screwdriver.
I just wish the instructions were better — be prepared to use your imagination at some points.
Like most other ACs on my list, it has multiple programmable user modes, including Auto Cool, Sleep, and Energy Saver modes. It also has a handy timer function.
Like the Frigidairemodel, the PerfectAire has a reusable filter. These things often slip my mind, so I love that there’s also an indicator light to tell me when to check the filter. Then all I have to do it gently wash the filter with dish soap and water.
PerfectAire does have one unique feature I like — the Follow Me thermostat.
The thermostat is embedded in the remote control and automatically sets the AC based on where the thermostat is.
Although this is a sliding and casement window AC, it can also work with narrow double-hung windows.
If you have an old home with narrow windows of any kind, this might just be the unit for you.
Who is the Perfectaire 3PASC10000 best for?
I recommend this Perfectaire 3PASC10000window AC for those looking to spend under $500 on their large room cooling.
Feature | Details |
---|---|
Energy Efficiency | 13 EER |
BTU Rating | 10,000 |
Weight | 72 lbs |
Dimensions | 23.5” x 14.8” x 21” |
Coverage Area | 450 sq. ft. |
Warranty | 1 year |
2. Koldfront CAC10000W - Cool + Dehumidify
Type: Horizontal Sliding / Casement
4.4
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Energy Efficiency
4.0
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4.7
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4.5
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Height
20.87"
Width
23.5"
Window Type
Horizontal Sliding / Casement
SEER
10.4
Pros
- Decently quiet
- Cooling power above its rating
- Energy-efficient
- Reliable operation
CONS
- Heavy unit
- No timer included
- Packaging problems
For those who live in the hot and muggy South, like me, an air conditioner that can dehumidify is essential.
The Koldfront CAC10000W fits the bill for extreme moisture removal and fantastic cooling.
Like the PerfectAire and Frigidairemodels, this 10000 BTU unit is meant to cool large areas of up to 450 square feet.
And cool, it does! I have live installed in my master bedroom, and sticky nights are a thing of the past.
I especially love that even in moderate temperatures, I can run it on “Dry Mode” to continue drawing moisture from my room.
Of course, the downside of this is that on super humid days, there is a lot of water dripping from the unit outside.
I ended up having to put some rock drainage below my window to keep it from seeping back towards the house.
Still, a small price to pay for powerful dehumidification and cooling.
Like the Frigidaire, this one is relatively quiet on low at 55 dB, but what really impressed me is its noise level of only 59 dB on high.
That’s much quieter than most portable ACs, but of course its far from being the quietest window AC when you compare with the traditional inverter compressor models
While I appreciate that Koldfront sends the entire installation kit with the unit, I still wish they were more upfront in their packaging on what additional items you’ll require beyond a screwdriver:
- A fine toothed saw
- An electric drill
- An extra set of hands
Like the Frigidaire, the Koldfront unit is hefty at 76 lbs, so I cannot stress enough having someone help you throughout the entire installation.
Who is the Koldfront CAC10000W best for?
This is the Koldfront CAC10000W horizontal window AC I recommend for people living in humid regions.
Feature | Details |
---|---|
Energy Efficiency | 11.0 EER |
BTU Rating | 10,000 |
Weight | 75 lbs |
Dimensions | 23.5” x 14.5” x 20.9” |
Coverage Area | 350 sq. ft. |
Warranty | 2 years |
3. FRIGIDAIRE FFRS1022R1 - Popular Model
4.3
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4.0
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4.5
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4.5
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Height
20.25"
Width
23.5"
Window Type
Horizontal Sliding / Casement
SEER
10.4
Pros
- Powerful cooling performance
- Plenty of user modes and options
- Remote control operation
- Simple usability
- Washable antibacterial filters
CONS
- Not suitable for standard windows
- Poor energy-efficiency
- Thermostat is sensitive to the sun
- Dim indicator lights
The Frigidaire FFRS1022R1 was initially my top choice for horizontal sliding windows, but I had to move it down my list a little bit because the company stopped producing this specific model.
Don’t fret, though! It’s still widely available on sites like Amazon, and I would not hesitate to buy this product.
The updated model by Frigidaire is also available, but it’s often sold out, which is why I’m still highlighting the FFRS1022R1.
The FFRS1022R1 (try saying that 10 times fast) has plenty of cooling power. With 10,000 BTU, it’s rated for rooms up to 450 square feet.
This was the perfect solution for a client who was looking for something powerful for their home theater room, because it’s also relatively quiet (for this type of unit) at 56 dB.
Usability is pretty simple, with push buttons on the unit and a remote control.
The display and indicator lights are pretty faint and hard to see, though, especially in daylight.
What I do like is the antibacterial filter.
I don’t have lab results to prove just how effective it is, but as an asthma sufferer, anything that actively removes outdoor pollutants from the air is welcome in my books.
It’s important for me to note that this unit is over 80 lbs, so when I client asks for this one, it’s a three-person job for my team.
One design flaw I’ve noticed is that direct sunlight seems to throw the thermostat off and make the AC run even if the indoor temperature is where it should be.
I have learned I can compensate by setting the target temperature a bit higher.
Overall, though, I think this is a great product.
Even though Frigidaire has updated their model, replacement parts are still easy to find as well, so I’d recommend choosing whichever Frigidaire model has the current best deal.
Who is the Frigidaire FFRS1022R1 best for?
I recommend this Frigidaire FFRS1022R1 for people who are looking for powerful cooling in large spaces from a trusted brand.
Feature | Details |
---|---|
Energy Efficiency | 10.4 EER |
BTU Rating | 10,000 |
Weight | 72 lbs |
Dimensions | 23.5” x 14.2” x 20.2” |
Coverage Area | 450 sq. ft. |
Warranty | 2 years |
4. Midea U MAW08V1QWT - Excellent for Vertical Sliding Windows
Type: Vertical Sliding Window
4.3
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Energy Efficiency
4.5
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4.0
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4.5
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Height
13.46"
Width
21.97"
Window Type
Vertical Sliding Window
SEER
15
Before I get started, I need to note that the Midea U is not for horizontal or casement windows.
I’m including it on my list for sliding windows because, when installed correctly, it has allows for one of the lowest profiles and still allows complete access to opening/closing your window, which is something that cannot be said about traditional window ACs.
My favorite feature of the Midea U is its U-shaped DC inverter technology, which essentially allows your window to slide between the control panel and the compressor, making it really, really quiet.
I’m talking only 38 dB on low mode, which is comparable to whispering.
Compared to the Koldfront model, which I still find reasonably quiet at 56 dB, the Midea feels almost silent.
I have this 8000 BTU model in my bonus room, which is currently outfitted as a playroom for my kids.
This size is perfect for the 300-square-foot room, but the Midea U does come in 10000 BTU and 12000 BTU varieties if you require a bit more oomph for your space.
Beyond the basic AC features, the Midea U is a smart home ac that can connect to both your phone and your voice-enabled devices, like Alexa.
Even though the Midea U has advanced technology, it’s still more affordable than all of the horizontal sliding casement ACs I’ve included, including my budget option from PerfectAire.
So, if you have a vertical sliding window, this is really the best option. You’ll see this one over and over on my lists of best window ACs.
Who is the Midea U MAW08V1QWT best for?
I recommend the Midea U MAW08V1QWT for folks who have standard vertical sliding windows but who want something that will still allow them to open/close the window as needed.
Feature | Details |
---|---|
Energy Efficiency | 15 |
BTU Rating | 8000 |
Weight | 55.56 lbs |
Dimensions | 13.46" x 21.97" x 19.17" |
Coverage Area | 350 sq. ft. |
Warranty | - |
5. Using a Compact Traditional Window AC With Modification
A lot of people want to avoid horizontal sliding window ACs for two reasons:
- They are expensive.
- They are big and bulky, making installation more challenging.
Sometimes, when a customer has a narrow casement window, I recommend using a compact traditional window AC unit.
A traditional window installation kit won’t work, but with a bit of patience, you can make a pretty nice custom frame for any window AC that isn’t too wide.
I was recently able to install this LG Dual Inverter window AC into a customer’s horizontal window of 20” as this unit is just under 19.6” wide.
This model has the same 10000 BTU power as the casement window ACs I’ve included, including the Koldfront and Perfectaire.
The benefit here is that it will cost less upfront. In my opinion, this is a better solution if you plan to keep your horizontal window AC installed for a long time or permanently, as it looks more natural.
There are a lot of tutorials out there on how to do this, but this is the general order in which I did this project:
Items I Used:
- Exterior grade plywood
- Pencil, measuring tape, and level
- ⅜” polycarbonate window (you could also use glass if you’re feeling fancy)
- Table saw and jigsaw
- Caulk Cord Weatherstrip
- Sander
- 1.24” interior framing and finishing nails
- Desired paint (make sure only exterior paint on the outside)
- Weather Seals
- Outdoor silicone caulk
- Window AC support bracket
- Window AC
Steps I Took:
1
The first thing I did was take out the existing window to use as a model for my new frame. I cut the plywood using a table saw to be just slightly taller than the window, so that I could wedge it up into the frame for a tight fit.2
I created a rabbet notch all along the edging so that it would fit with my existing window frame. I applied Caulk Cord Weatherstrip to this.3
I cut holes for the new polycarbonate window and the AC unit. If you don’t mind losing your window space, feel free to just have a larger piece of plywood without a window.4
I sanded down everything and painted it before adding the window pane.5
I installed the window pane to the plywood, and then fit the entire piece to the window frame, using interior framing and finishing nails to make it look for aesthetically pleasing and secure. This is what makes this option a much more permanent solution.6
Next, I installed a window AC support bracket. The LG Inverter model I used didn’t come with one, but there are some really solid brackets online that even have built in levels, which I really appreciate when I already have my hands full!7
Once the bracket was in place, I installed the window AC according to its directions.8
Last, I used self adhesive weather stripping to fill in any gaps, and I finished with a silicone exterior caulk on both the inside and outside of the unit.
LG Dual Inverter Window AC - Requires Modification
Feature | Details |
---|---|
Energy Efficiency | 15 |
BTU Rating | 10000 |
Weight | 63 lbs |
Dimensions | 12.5" x 19.6" x 24.5" |
Coverage Area | 450 sq. ft. |
Warranty | - |
6. Using a Traditional Portable AC With a Specialized Window Kit
The last option on my list for horizontal sliding or casement windows is to use a traditional portable AC.
Most of these units are meant to vent out a standard window, but there are a few exceptions that make this the easiest solution for many people.
With that said, the easiest isn’t always the best. The downsides of using a portable AC include:
- Losing valuable floor space to accommodate the appliance.
- Less energy efficiency than window units.
- Louder than window units.
Whenever a customer asks me about using a portable AC in a horizontal sliding window, I recommend the Serenelife SLACT108.
It has an adjustable window plate that can be installed vertically up to 37” in horizontal sliding windows.
It’s as easy adjusting the plate to size, fitting it in the window opening, and closing the window on it for a secure fit.
Another benefit of the SereneLife is that it is the only option on my list that also functions as a heater.
And like the Koldfront model, it’s also a powerful dehumidifier, making this portable AC option great for places with large temperature swings, such as garages.
Using a portable AC in a casement window is a bit trickier, but not impossible.
There are window seal vents that are made from a tent-like fabric, that can be fitted to these windows and have built-in vent holes.
Related Article: Top Rated AC Seal Kits Reviewed
I really only recommend this option as a temporary solution such as an event or emergency cooling.
The fabric is not completely airtight, so it will allow some of your cool air to escape, making the AC even less efficient.
On top of that, it’s not weatherproof, and can definitely let rain seep in uninvited.
SereneLife Portable AC - Requires Modification
Feature | Details |
---|---|
Energy Efficiency | - |
BTU Rating | 10,000 |
Weight | 56.48 lbs |
Dimensions | 32.1" x 17.4" x 13.4" |
Coverage Area | 350 sq. ft. |
Warranty | - |
Comparing The Features Of Sliding Window ACs
Preview | Name | Rating | BTU | Dimensions | Price |
---|---|---|---|---|---|
PerfectAire 3PASC10000 | 4.5 | 10,000 | 23.5” x 14.8” x 21” | ||
Koldfront CAC10000W | 4.4 | 8,000 | 23.5” x 14.5” x 20.9” | ||
FRIGIDAIRE FFRS1022R1 | 4.3 | 10,000 | 23.5” x 14.2” x 20.2” | ||
Midea U MAW08V1QWT | 4.3 | 8,000 | 13.46" x 21.97" x 19.17" | ||
LG LW1022IVSM | - | 10,000 | 12.5" x 19.6" x 24.5" | ||
Serenelife SLACHT108 SLPAC | - | 10,000 | 32.1" x 17.4" x 13.4" |
Horizontal Vs Vertical Sliding Window ACs Explained
I know shopping for a sliding window air conditioner can be confusing.
These air conditioners have many names, like horizontal and vertical window ACs and casement window AC units.
What’s the difference? It all comes down to shape.
A horizontal AC, or horizontal window AC, is your typical sliding window air conditioner.
These units are wide rectangular boxes that fit a classic double-hung window that (confusingly) slides vertically, or a crank window that opens upwards.
ACLAB Note:
If you do not have the right window type for either traditional or casement AC, consider getting a through-the-wall AC.
A vertical air conditioner, or vertical window air conditioner, is a narrow and tall window AC unit.
This shape allows them to mount to horizontally-opening slider windows where a traditional horizontal AC won’t fit.
Finally, casement window air conditioners are the same as vertical window AC units. You can install these machines into casement windows that open on hinges. You just have to remove the glass panel before installation.
Related Article: Best Saddle U Shaped ACs Compared
How To Find A Quality Air Conditioner For A Sliding Window
The following is a shorter version of our more comprehensive Window AC Buyer's Guide.
Cooling Power Vs Area Coverage
The power of a casement air conditioner is rated in two ways — British thermal units (BTU) and coverage area. A higher BTU translates to a larger coverage area. [1]
I recommend looking for casement air conditioners with at least an 8,000 BTU/350-square-foot rating.
The ultimate choice depends on the size of the room you want to cool, though, so it’s a good idea to carefully measure it ahead of time and also consider ceiling height.
Size & Weight Of The Unit
Most air conditioners for windows come with covers to block any remaining window openings, but I advise buying a unit that’s as close to the size of the window as possible.
Horizontal sliding and casement window ACs are definitely heavier than their standard window AC counterparts, so I always emphasize not taking on this job alone. For example, the Frigidaire unit I included is 80lbs!
ACLAB Note:
The heavier the unit, the harder its installation. Take proper measurement of the window before buying a vertical window air conditioner.
Location Location Location
Aim toplace your slider window air conditioner in a shaded window without any trees or other obstructions within two feet.
Direct sunlight can overheat the air conditioner and reduce its effectiveness, while trees or bushes can impede proper airflow.
ACLAB Note:
Also, remember that most AC units only have six-foot power cords. You should never use an extension cord with a window air conditioner, so choose a window that has a nearby wall outlet.
Look For Filtration/Dehumidification
I recommend choosing a sliding window air conditioner with an advanced filtration system, like the Koldfront unit.
Proper filtering (ideally antibacterial) prevents your AC from drawing contaminants indoors and maintains high air quality, which is particularly important if you live with breathing conditions as I do.
If you live in a humid region, it may be worth picking an air conditioner with a dehumidification function.
This can help maintain healthy indoor humidity levels and prevent dust mites and mold growth.[2]
ACLAB Note:
An AC with a robust air filtration system and dehumidifier is recommended. A good air filtration system can help keep the air clean and a dehumidifier can help remove excess moisture.
Energy Efficiency Matters!
Try to find a window air conditioner with the highest possible energy efficiency ratio (EER) rating.
This rating is simple to understand — the higher the EER number, the more efficient the unit is.
I would aim for an EER rating of at least 10, like on the Koldfront and PerfectAire units. If the AC has an Energy Star certificate, that’s just further proof that it won’t drain your wallet.
Related Article: Learn How Much Energy a Window AC Uses
Noise Levels (Decibels) - The Lower The More Comfortable
There’sno such thing as a silent window air conditioner, but some units are quieter than others.
My recommendation is to look for an AC with a running noise of around 55 dB, like the Koldfrontor Midea models.
This noise level is about equal to a regular conversation and isn’t too distracting during normal life (except maybe in the bedroom). [3]
Ease Of Installation & Maintenance
I would pick a unit that comes with a full installation kit, like the PerfectAire.
Vertical AC units can be really heavy and installing them is usually a two-person job. Having mounting frames and other parts custom-made for your unit can make fixing the unit to the window sill much easier.
ACLAB Note:
Window AC filters should be replaced or washed once a month. Find a unit with washable filters so you won’t have to buy new ones as often.
When you change the filter, it’s smart to clean the cooling coils at the same time — they’re usually right under the filter and you can use a brush vacuum to get rid of any dirt.
Warranty (1 Year Plus)
Choose a sliding window air conditioner with at least a one-year warranty.
All of the units I’ve listed have a year-long warranty or longer, just in case something goes wrong with the unit. Yet, it’s still worth comparing the fine print.
Comparing Sliding Window With Other AC Types
Type | Max Room Size | Most Common BTU | Dehumidifier | Running Costs | Price |
---|---|---|---|---|---|
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) | $$$$ |
FAQs
Is It Safe To Use Extension Cords To Run Sliding Window Air Conditioners?
Using extension cords with sliding window air conditioners is generally not safe. All extension cords can’t handle their high power consumption and could pose a fire hazard.
Can I Put An AC Unit in a Horizontal Sliding Window?
You can install an AC in a horizontally sliding window, but you must buy a specific type of window air conditioner. Confusingly, these units are called vertical or casement window air conditioners, because they’re tall and narrow — which makes them vertically bigger than regular window ACs.
Can I Mount A Standard AC On A Sliding Window?
You can mount a regular window air conditioner on a horizontally sliding window if the unit fits in the window frame. You’ll have to make a DIY frame to block the large window opening, which may decrease the unit’s efficiency.
Can I Install A Portable AC In A Casement Or Sliding Window?
Yes, you can install a portable air conditioner in a casement or sliding window using the same duct panel you’d use with a double-hung window. You may have to use some duct tape to secure the panel, but they work all the same whether mounted horizontally or vertically.
How Can I Fill In The Gap Left Between The Unit And The Upper Window Frame?
Most window AC units come with an accordion panel and foam strips to cover the gap left behind by the installation. If your window air conditioner didn’t come with a panel, you can buy cheap foam insulation board at a hardware store, cut it into shape, and attach it with duct tape.
Do I Need A Professional HVAC Technician To Install A Sliding Window Air Conditioner?
You don’t need an HVAC professional to install sliding window air conditioners. If you can’t lift the heavy AC units, though, you may need someone to help you. I also recommend checking with HOA, landlord, or any other relevant authority whether you’re allowed to install window ACs, especially if you rent.
Can I Use An AC Without Putting It In A Window?
You can use a window air conditioner without putting it in a window if you can build an exhaust and water drainage system for it. Many portable air conditioners can also be run without window installation. However, this will often compromise their cooling efficiency, so I don’t recommend it.
Summary - What To Buy?
There are plenty of options for fitting a window AC in a horizontal sliding or casement window, but some options stand out as true winners to me.
My top choice for this setup is the PerfectAire model.
Not only is this 10000 BTU powerful enough to cool spaces of up to 450 square feet, but it also comes within everything you need for installation and is the most budget friendly!
My #1 Recommendation
PerfectAire 3PASC10000
- Powerful cooling performance
- Plenty of user modes and options
- Remote control operation
- Simple usability
- Washable antibacterial filters
References:
- https://www.totalhomesupply.com/air-conditioner-btu-calculator
- https://www.epa.gov/mold/mold-course-chapter-2
- https://hearinghealthfoundation.org/decibel-levels