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Window Air Conditioners

Window air conditioners are one of the most common types of air conditioners, and most people are at least somewhat familiar with them. Here is a quick recap and general description of what a window air conditioner is:

These units sit in a window and are generally designed to cool just one room. They generally consist on just one "box" that contains the cold side of the air conditioner on the inside of the window and the hot side is on the outside. They usually range in BTU from around 5,000 BTU to around 18,000-20,000 BTU. Generally, they are not as energy efficient as split units, but they are usually less expensive to purchase and a professional installation is not usually required.

Window air conditioners run off either 120 Volt/ 60 Hz circuits or 220/240 Volts/60 Hertz circuits. Generally speaking units with a BTU below 15,000 use 120 Volts. Units with greater BTU ratings usually use the higher Voltage.

Window air conditioners are given EER ratings to denote their energy. An EER of 10.0 or greater is considered good.

One other factor to note is that window air conditioners are generally good at cooling one room, but more that one room, or even large rooms can present problems. Despite the fact that you can get window air conditioners with relatively high BTU levels, they are still putting out their cooling from just one location- the window in which they are installed. For this reason, it is usually better to go with several different window units or a central air conditioning system with several duct outlets for cooling multiple rooms or a very large area.

Choosing a window air conditioner

If you've decided a window air conditioner is what you would like to go with, here are some of the most important factors to consider when choosing what unit to purchase:

  • Your BTU requirements- This is probably the first and most important consideration. You want to get a unit with a capacity as closely matched to your needs as possible. A unit that is not powerful enough will run constantly and will never properly cool the room. A unit that is too powerful will "short cycle"- it will cycle on and off over and over again, only remaining on for short periods of time. Short cycling is bad for the compressor- it could substantially shorten the life of the air conditioner, and the air conditioner will not dehumidify appropriately- so while the air in your room might be a comfortable temperature, there could be an uncomfortable level of humidity. The ideally sized unit will run at its maximum capacity on the few hottest days of the year and run somewhat under capacity at other times
  • Your window size- be sure to pick a window air conditioner that will fit your window. Note that window air conditioners come with installation kits to fit certain common window sizes- just because the unit will fit in a window does not mean that the installation kit will fit.
  • The energy efficiency and energy requirements- You should be mindful of the EER of the air conditioner that you choose. A higher EER is better, and a higher EER air conditioner often costs less in the long run than a less efficient unit. Additionally, many local utility companies offer discounts on high EER air conditioners. As far as electrical requirements, most air conditioners do have robust energy needs, and even if the unit you are purchasing does not require a 220 Volt outlet, you might want to make sure that it can have a dedicated circuit (otherwise, if you run other high amperage appliances on the same circuit, you might trip a breaker). Of course, you should at least make sure you have the appropriate electrical connection (120 Volt or 220/240 Volt) before purchasing the air conditioner.

Once you've decided on some of the above factors, you may want to consider other features that can add to the convenience of the air conditioner:

  • Air filtration- all models have some form of air filter. Better models have better filters that can clean your air while air conditioning
  • Remote control- some units can be controlled from across the room
  • Manual vs. electronic controls- manual models are generally less expensive and can be simpler to use, but electronic models usually offer more advanced features
  • Slide-out vs. fixed chassis- models with a slide-out chassis are easier to install
  • Noise level- though many of today's air conditioners are quieter than older models, you still might want to consider their noise level. Often noise levels are given in Decibel ratings. The higher the Decibel level, the louder the unit is, and every 10 decibel increase is an increase in the sound pressure by a factor of ten (60 Decibels is 10 times louder than 50 Decibels and 100 times louder than 40 Decibels, for example)
  • Timer and sleep function- a timers allows you to save energy by only running the air conditioner at set times. For example, you might set the air conditioner only run when you anticipate being at home- and not wasting energy by cooling your room when no one is in the room. Sleep timers also help save energy by cooling less after the air conditioner has been running for a set time. This way, you set the air conditioner to run while you are going to sleep and it continues running while you sleep, but at a lower level (i.e., the temperature in the room is allowed to rise a bit) while you sleep
  • Air output- almost all models have at least two different settings for airflow. You might want more settings to increase the versatility of cooling. Also pay attention to the Cubic Feet per Minute (CFM) rating. CFM is a measure of the volume of air blown. The higher the CFM, the more airflow the unit kicks out
  • Air flow options- During normal operation, window air conditioners remove the heat and moisture from the air inside a room and expel that heat outside. Other than small leaks that are inherent in any (non-hermetically sealed) room, there is no air exchange. Air inside the room stays inside. Air outside the room stays outside. Some air conditioners offer venting options that allow you to get some fresh air circulating
  • Heating options- Some window air conditioners can heat as well as cool. This can be useful in the winter time- enabling you to use your air conditioner year-round
  • Louver adjustability- the more ways you can adjust the louvers (up/down, side-to-side), the more options you have for directing airflow. Also, some units can be set to "swing", so they blow out cool air from several different positions.
  • Air conditioner physical size and appearance- some air conditioners are smaller and/or more pleasing to the eye than others.


Window air conditioners come with installation instructions and installation kits, but below are a few factors to consider for installation. Please follow the instructions included with your window air conditioner for specific installation instructions and recommendations.


Window air conditioners should be installed into a window that is not in direct sunlight (otherwise the sunlight hitting the cabinet will increase the heat load on the unit). If you must put it in a window that is exposed to direct sunlight, you may want to consider building some sort of hood or awning to relieve some of the heat. Most of the window air conditioner will be on the outside of the window. On the outside, the back of the window air conditioner should have at least 12" of clearance. The bottom should have at least 4" of clearance. The air conditioner should be tilted a bit towards the outside, so that condensate (water condensed out of the air) can drip out. The window air conditioner will come with an installation kit that includes support brackets for the air conditioner, filler kits to be installed alongside the air conditioner, and all necessary hardware.

Installation Questions

What is the difference between a slide-out chassis and a fixed chassis?
See the picture of a window air conditioner with a slide-out chassis below:

A window air conditioner with a slide-out chassis has an outer cabinet that can be detached from the rest of the air conditioner. This can come in handy when installing the air conditioner into a window- instead of balancing 150 pounds of air conditioner while you install support brackets, you can just install the light outer shell. Once the outer shell is completely installed, simply slide rest of the air conditioner in place.

A fixed chassis air conditioner has a cabinet that cannot be detached for installation.

My window air conditioner is making splashing noises. Is it defective or did I incorrectly install it?

Many window air conditioners make some quiet splashing noises when they are running. This is because they use the condensate water to help cool the compressor before it drains off. These air conditioners use a "Slinger System" to splash water onto the compressor. If this noise bothers you, check your owner's manual- you may be able to drain off the water before it is slung onto the compressor. However, this might decrease the performance of the air conditioner.

Do window air conditioners fit casement (crank-out) or sliding windows?

Most window air conditioners are designed to fit standard double-hung windows. For windows that slide side-to-side, there are special window air conditioners, but they are usually more expensive than the "normal" kind. Otherwise, if your window opening meets the dimensions noted by the air conditioners specifications, then the air conditioner should fit.

Currently there are few options for window air conditioners for casement (crank-out) windows. You might try a mini-split or portable air conditioner, although there may be some extensive installation required for either of those units.

Can't I just turn a window air conditioner on its side to fit my slider window?

No. Turning an air conditioner on its side and running it is a very good way to quickly break it.

Can a window air conditioner be installed through a wall?

Most window air conditioners can be installed through a wall, if the hole in the wall is sized appropriately. However, it is recommended that you check with the manufacturer and/or the owners manual of the window air conditioner before attempting this type of installation. When in doubt, you may want to check with a contractor to perform this service.

Also please note that there are air conditioners that are specifically designed for through-the-wall use. You may want to look into one of these models for a through the wall installation.

Why are the maximum and minimum window opening dimensions different than the actual dimensions of the air conditioner?

Window air conditioners come with installation kits to securely hold them in your window and to fill the rest of the space on the sides that is not filled by the air conditioner itself. For this reason, the window dimensions that the air conditioner will fit vary from the actual physical dimensions of the air conditioner.

More information on window air conditioners: How to Buy a Room Air Conditioner
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