It is not easy to get a good window air conditioner to fit a horizontal sliding window (also referred to as casement window AC). These ACs are vertically mounted unlike the standard window units to fit in the sliding or crank-out windows.
We have compiled below the best slider window air conditioners all of which fit in horizontal sliding windows with an emphasis on efficiency and low noise.
Following the brief comparison table, there are in-depth reviews that point out BTU capacity, room size coverage, noise levels, energy ratings, and special features such as Wi-Fi connectivity, remotes, and others (where applicable).
The table below gives you a quick comparison of our 5 best choices of horizontal sliding window air conditioners
| Air Conditioner | BTU | Noise Level | Energy Efficiency |
|---|---|---|---|
| Frigidaire FFRS0822S1 8,000 BTU Slider Window AC | 8,000 BTU | 48 dB | EER 10.8 |
| Keystone KSTSW10A 10,000 BTU Slider AC | 10,000 BTU | 55 dB | EER 10.4 |
| Koldfront CAC10000W 10,000 BTU Casement AC | 10,000 BTU | 56-60 dB | EER 10.4 |
| Perfect Aire 10,000 BTU Slider Window AC | 10,000 BTU | 55+ dB | SEER 13 |
| Midea Arctic King 10,000 BTU Slider AC | 10,000 BTU | 50 dB | EER 10 |
#1 Frigidaire FFRS0822S1 8,000 BTU Slider/Casement Window Air Conditioner
The Frigidaire FFRS0822S1 8,000 BTU Slider Window AC is frequently considered the best all-around casement-window air conditioner because of its combination of powerful cooling, low noise, and price.
This is a unit that is specifically designed to fit horizontal sliding or crank-out windows and can comfortably cool an area of 350 sq ft (which is ideal to cool a medium-sized room). Users and professionals rave about its whisper-quiet operation – around 48.4 dB on low, which is comparable to the sound level of a library conversation.
This is why the Frigidaire is a good option to use in bedrooms or home offices where low noise is of importance.
Although it is relatively small with an output of 8,000 BTU, the Frigidaire FFRS0822S1 is a powerful cooling system with an Energy Efficiency Ratio of about 10.8. It has three cooling speeds, a multi-speed fan and modes such as a 24-hour programmable on/off timer and Sleep Mode to save energy and provide overnight comfort. The supplied full-function remote control allows you to change temperature and fan settings at the other side of the room.
The Ready-Select electronic controls are also easy to dial in your preferred settings, which is a plus to the users.
This slider AC is heavy duty and has adjustable side panels and mounting hardware to fit sliding window openings. It has an easily accessible (tilt-out) washable filter that can be cleaned regularly to keep it efficient and clean the air. The Frigidaire weighs about 70 lbs (a typical characteristic of a casement unit) so a support bracket and an extra hand during installation is suggested. When installed, it works without problems and even has an Energy Saver mode which switches the compressor on and off to save power.
It is not ENERGY STAR-certified, but it is fairly efficient as far as its type is concerned.
#2 Keystone KSTSW10A 10,000 BTU Slider Casement Window Air Conditioner
In case you are concerned about having to lift a heavy AC into your slider window, then the Keystone KSTSW10A 10,000 BTU Slider/Casement AC is a game changer.
This model is also significantly lightweight (approximately 34 lbs, or half the weight of most other casement units) and is much easier to install. Although it is lighter, the Keystone has the full 10,000 BTU of cooling capacity, which is sufficient to cover areas up to ~450 sq ft (approx. 20 x 22 ft room).
It is a special window designed to fit horizontal sliding or crank windows and it is supplied with the required window kit and bracket to install it securely.
Keystone KSTSW10A has three fan speeds and three cooling modes (cool, dehumidify, fan-only) and a convenient Sleep Mode that allows the gradual change of temperature at night. It also has 4-way adjustable air direction so that you can direct cold air where you want it. The unit has a remote control and digital thermostat that enables you to adjust the temperature and fan speed of your choice across the room. Noise wise, the Keystone operates at a typical noise level of a window AC (mid-50 dB), which is quiet enough to most living spaces.
Although it is not as quiet as the smaller Frigidaire, the sound is quite bearable by most users, and is like background white noise.
Energy efficiency is good at an EER of about 10.4 (a little lower than some of the smaller units, so it is not ENERGY STAR qualified). But the Keystone compensates that by having such features as the Energy Saver mode and a 24-hour programmable timer to prevent unnecessary cooling when it is not necessary. The easy-clean washable filter helps to trap dust, which is a useful feature to allergy sufferers, and provides a constant flow of air. The first limitation is that Keystone only sells this model in 10,000 BTU, so unless your room is very large ( 400-500 sq ft), you may find yourself with more capacity than you need (in this case an 8,000 BTU unit is an option).
#3 Koldfront CAC10000W 10,000 BTU Casement/Slider Window Air Conditioner
The Koldfront CAC10000W 10,000 BTU Casement AC is a feature-rich vertical window air conditioner that fits in the sliding window and is famous because it comes with everything you need in the box.
Koldfront CAC series is available in 8,000 BTU and 10,000 BTU models, which are appropriate to rooms that range between 300 and 450-500 sq ft.
Among the greatest benefits of this model is that it comes with a full installation kit, which means that you do not have to purchase an additional window insert or side panel kit in most cases because it comes with mounting hardware and weather strips.
The cooling power is good: the 10k BTU unit can rapidly cool a 450 sq ft area, whereas the 8k BTU one can cool a 350 sq ft area. The unit has three fan speeds and cool, fan-only, and dehumidifier modes to make it versatilely comfortable. It also has a clear digital display and an adjustable thermostat and it also has a full-function remote control (16-ft range) to make it convenient. The Koldfront features helpful additions such as a Sleep Mode that makes it run more quietly and more economically at night, and an Energy Saver mode that switches the compressor on and off to keep the temperature steady with less energy.
The Koldfront 8,000 BTU has a great EER of 11.0 and is Energy Star rated, so it is one of the more efficient casement air conditioners on the market. The 10,000 BTU model has a slightly lower EER 10.4, which is just below Energy Star, which is normal as BTUs go up.
Remember that Koldfront CAC series is known to be slightly louder than its competitors. It is loud, according to many users, and particularly on higher fan settings, which are in the range of about the upper 50s in decibels (about a box fan or light conversation). This may be a factor in case you intend to use it in a bedroom or require quiet operation to be ultra-quiet. But in the case of living rooms, garages, or when you do not mind a bit of white noise, the compromise is that you get one of the most feature-rich slider ACs in the market.
#4 Perfect Aire 10,000 BTU Slider Casement Window AC (Model 3PASC10000)
In case you are interested in energy efficiency in a sliding window AC, the Perfect Aire 10,000 BTU Slider Window Air Conditioner is a great choice since it has an outstanding SEER 13 efficiency rating, which is among the best in this segment. This implies that it can provide more cooling per watt of electricity and this can help to keep the power bills down during hot summers. It comes in a single 10,000 BTU model that is suitable in rooms of about 400-450 sq ft.
Perfect Aire made this unit to fit casement and horizontal sliding windows and it comes with an expandable window mounting kit that fits widths of approximately 15.5-inches to 16.25-inches and heights of 21.25-inches to 39.5-inches, so it fits snugly.
In addition to being efficient, the Perfect Aire 3PASC10000 is a balanced product in terms of features. It also has 3 cooling speeds, 3 fan-only speeds, and a special Auto and Sleep Mode. One of the features is the “Follow Me” remote control – this remote has an in-built temperature sensor, so once it is pressed, the AC will adjust the room temperature to the temperature at the remote location (it is basically sensing the temperature at the location of the remote).
This provides a more balanced cooling particularly in bigger rooms. It also has a 24-hour programmable timer and maintenance-friendly, tilt-out washable filter. Regarding cooling capacity, users report that it cools the mentioned area range well, but Perfect Aire adds that when the temperature is very high (e.g. when the outdoor temperature is very high), this unit might not perform as well when pushed to the extreme.
Noise is the primary tradeoff of all that efficiency. This AC is not the most silent one in the category. The compressor and high efficiency fans give out a constant sound that is audible, particularly at high fan speed. It is similar to numerous 10k BTU (mid-50s dB on low to low-60s dB on high).
Unless you are insensitive to noise, you may prefer the quieter Frigidaire, however, in case you are considering using it in a bedroom. However, in occupied spaces or in case you are used to sleeping with white noise, the hum of the Perfect Aire should be tolerable. The positive side of that little hum is that it is a very efficient operation, the Eco Mode will switch the compressor off once the desired temperature is achieved, saving energy by only switching the fan on and off (which also helps to reduce noise at times).
Simply bear in mind that, in this model, you sacrifice a little bit of silence, it is a bit louder than some of the competitors, so you should consider how much noise you can put up with and where you will place it.
All in all, Perfect Aire provides a cool, effective breeze that is difficult to match in case you are concerned with the low consumption of electricity.
#5 Midea Arctic King 10,000 BTU Slide Casement Window Air Conditioner
Midea is a leading manufacturer of air conditioners in the world and the Midea Arctic King 10,000 BTU Slider AC is a reliable no-frills air conditioner by this reputed company. This 10k BTU casement window air conditioner is sold under the brand name of Arctic King (a Midea brand) and is rated to cool rooms of up to ~450 sq ft (approximately a 20′ x 22′ area) and so can be used in bedrooms, living rooms or apartments with horizontal sliding windows.
It is designed to suit the tall, narrow frame required to install slider/casement and it is supplied with a window kit and panels to seal gaps around the unit.
The Midea/Arctic King provides everything you would want. It has three cooling speeds and three fan speeds, a 24-hour on/off timer and Sleep Mode to cool gradually overnight. The digital controls and the remote that comes with it enables you to control temperature, fan speed and mode across the room.
The Midea Arctic King 10k has average noise and efficiency by its class. It does not have any special marketing as being ultra-quiet, so you can anticipate a low hum when it is operating (comparable to other 10,000 BTU units, about 55-58 dB range depending on fan speed). The majority consider it to be white-noise-like and non-obtrusive in living quarters; in a bedroom, light sleepers may hear it but many adapt to the noise. The unit has an estimated EER of about 10.0 and is not ENERGY STAR certified on energy.
It does have an Energy Saver mode, to assist in reducing power consumption by cycling the compressor, but its efficiency is more average.
What to Consider When Choosing a Horizontal Sliding Window AC
Get the right BTU capacity of the AC to the size of the room to get the best cooling.
Another rule of thumb is approximately 20 BTUs per square foot of room area. As an example, 8,000 BTU unit will cover approximately 300-350 sq ft, 10,000 BTU will cover approximately 450-500 sq ft. Each of the above models gives a rough coverage area; do not over size (which may cause the unit to short-cycle) or undersize (which will not be able to cool the area).
Horizontal sliding window ACs are vertical and they fit narrow windows (usually about 15” to 16”). To make sure that the unit and its installation kit will fit, measure your window opening (width and height). All of our suggestions include a window kit or panels that can be adjusted to a specific range (e.g. 21″ to 39″ height). In case your window is either too tall or too short, make sure to check the product specification to fit. Majority of slider ACs are not designed to fit windows that move up/down, but side-to-side.
Ensure that the Energy Efficiency Ratio (EER) or Combined Energy Efficiency Ratio (CEER) is checked. The larger the numbers, the more cooling per watt (i.e. lower operating cost). A few 8,000 BTU units (such as Koldfront) have EERs of 11 and even some are Energy Star, compared to 10,000 BTU sliders with EERs of 10-10.5. The SEER 13 of the Perfect Aire is quite high and this means that it has a good seasonal efficiency.
All window ACs are noisy but it varies. To use in a bedroom or a quiet office, seek models that are labeled as low-noise or have dB ratings in the upper 40s and lower 50s at low fan speed. One of the quietest in this category is the Frigidaire ( 48 dB on low), which is perfect to use by light sleepers. Bigger 10k units will normally give 55-60 dB on high which is approximately the sound of background TV or conversation.
Newer slider window ACs have digital thermostats, remotes and several modes. Convenience is provided by a remote control in all our top picks. Others such as Perfect Aire include sophisticated remotes with temperature sensors. Automatic operation is convenient with Timers (to switch on/off), Sleep modes (to gradually change temperature to make it comfortable).
