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Window Air Conditioner Buying Guide

Window AC Buying Guide

As the cost of cooling homes continues to rise and the emphasis on greener household appliances grows, many people are looking toward more efficient cooling alternatives than their decades-old central air conditioners. As one good alternative, window air conditioners provide effective room cooling in space-saving packages. These appliances are designed to install inside vertical-opening windows or custom-created wall spaces.

Window air conditioner models are completely self-contained, require just a few easy-to-manage accessories, and are designed with green principles in mind. These systems are much more energy efficient and kinder to the environment than their early counterparts. Often carrying high Energy Efficiency Ratios (EERs), boasting Energy Star certifications, and using eco-friendly refrigerants, window ACs cool rooms with little impact on your power bill and carbon footprint — especially if you offset operation by limiting use of your central AC. To set up, all you need is an appropriately sized window (or wall space), a warm room, and an urge to relax in a cool environment on a hot summer day.

For easy access to the topics in this buying guide, use our topic list below:

About Window ACs

Comfort-Aire RAH-123G Window Air Conditioner

Window air conditioners, also known as room air conditioners, are self-contained cooling systems designed to cool one or two rooms at a time. Traditionally, these units mount semi-permanently inside standard vertical sash or double-hung windows or permanently inside a measured and prepared wall opening. Specially designed window air conditioners can be installed inside sliding windows, although these are less popular and more expensive than traditional models. Window ACs typically cannot be installed inside casement (or crank) windows, unless you make hefty modifications to the window frame.

A window air conditioner contains the three basic parts of an air conditioner: a compressor, a condenser coil, and an evaporator coil. A standard window AC also features two motorized fans, an expansion valve, an air filter, a manual or digital thermostat, and a control panel. To cool your room air, window air conditioners use refrigerant, a chemical compound that is used in cooling systems to absorb heat from its surroundings. This is a key ingredient in the cooling process that has recently become an important consideration when choosing an eco-friendly appliance.

All window air conditioners work in the same fashion. They cool by extracting hot and humid air from a room, cooling and dehumidifying it, and returning it back into the room while exhausting warm air to the outside. In more technical terms, a window air conditioner uses its compressor to compress refrigerant into a hot, high-pressure gas. The refrigerant gas then travels through the condenser coil, where it is condensed into a liquid and sent through the expansion valve and over the evaporator coil to absorb heat and cool down. Hot air is exhausted out through the back of the air conditioner — the part facing the outside — while cool air is blown into your room using the air return grille located on the front of the system.

Most window air conditioners use an air filter during the cooling process to remove large particles from the air and deliver a certain amount of purified air to your space. The units are controlled by manual or electronic control panels — situated on the front of each unit — that allow you to select your desired temperature using the onboard thermostat, choose a cooling speed, and in some cases, program timed operation.

Energy Efficiency

Window air conditioners are more often used as the primary source of cooling for small spaces that aren't covered by a central AC. However, it's not unusual for consumers who regularly use central air conditioning units to look to window air conditioners as a way to cool rooms using less energy during the warmer months. These systems typically cost less to purchase initially and less to operate over the long-term if sized correctly for your space. Look for two things when evaluating a unit's energy efficiency:

  • Energy Star Seal — Energy Star room air conditioners use at least 10 percent less energy than conventional models. These systems are often loaded with useful features to give you greater temperature control and make energy consumption easier to manage. These features include programmable timers, digital thermostats, automatic cooling modes, and multiple cooling speeds. The Energy Star program estimates that if every room air conditioner sold were Energy Star-certified, it would prevent 800 pounds of greenhouse gas emissions annually. This is roughly equivalent to the emissions of more than 66,000 cars.

  • Energy Efficiency Ratio — An EER measurement is another efficiency indicator for room air conditioners, and it's gaining popularity across the window AC industry. This ratio tells you how many British Thermal Units (BTUs) of heat energy a window AC uses for each watt of power. As a rule of thumb, remember the higher the EER, the more efficient the air conditioner. Typically, every 0.1 increase in EER translates into a 1 percent drop in your electricity usage. To achieve the best energy- and cost-savings, the U.S. Department of Energy recommends that you shop for a room air conditioner that has an EER of at least 10.0. Window ACs manufactured by Friedrich and Sunpentown are known for both their high EERs and Energy Star seals.

What to Consider When Choosing a Window AC

There are many things to consider when choosing a window air conditioner for your room. Some are minor and involve personal preference while others are major and take into account what type of AC your environment will support. In general, you should consider three major points when deciding among models — cooling capacity, installation type, and electrical requirements.

Cooling Capacity — The cooling capacity of a room air conditioner is measured in BTUs (British Thermal Units) per hour. To ensure high efficiency, choose an air conditioner with a BTU level designed to fit the square footage of your room or space. This is necessary to avoid a couple of common scenarios. If you use a window air conditioner that doesn't have enough BTU power to cover a large room, it will work overtime to try and bring the temperature down. In the process, it will waste energy dollars. In contrast, a window AC that has too large of a BTU capacity for your space will cool it, but it won't remove as much humidity from the air as a properly sized unit should. This will make your room feel damp and clammy.

To find the right cooling capacity for your room, determine the square footage of your space. Then, use the chart below to find your ideal BTU measurement.

Area To Be Cooled (Square Feet)

Capacity Needed (BTUs Per Hour)

100 to 150 square feet

5,000 BTUs

150 to 250 square feet

6,000 BTUs

250 to 300 square feet

7,000 BTUs

300 to 350 square feet

8,000 BTUs

350 to 400 square feet

9,000 BTUs

400 to 450 square feet

10,000 BTUs

450 to 550 square feet

12,000 BTUs

550 to 700 square feet

14,000 BTUs

700 to 1,000 square feet

18,000 BTUs

1,000 to 1,200 square feet

21,000 BTUs

1,200 to 1,400 square feet

23,000 BTUs


To determine the most accurate BTU estimate, you should also consider these factors:

  • Ceiling Height — The above estimates assume you have traditional 8-foot ceilings. If your ceilings measure higher than 8 feet, you'll want to increase your BTU level.
  • Sunlight — If your room or space is sunny during the day, increase your BTUs by 10 percent.
  • Shade — If your room is shaded for most of the day, decrease your BTUs by 10 percent.
  • Number of Occupants — If more than 2 people will occupy your room or space regularly, you should add an additional 600 BTUs of cooling power for each person.
  • Kitchen — If you are installing your window AC in a kitchen, increase the BTU level by 4,000.

Installation Type — When deciding among window air conditioners, you should also consider where you will install the unit. The most popular window AC models are designed to fit inside double-hung — or vertical opening — windows. These same models can also be installed inside a custom-created wall space using special mounting hardware. This is a useful alternative if your window's dimensions are too small or too large, if you don't have double-hung windows, and if you're willing to perform the extra work necessary to create a wall opening.

  • Window Installation: When installing a unit in a double-hung window, you'll need to measure the dimensions inside your window frame exactly, paying special attention to the width. With these measurements in hand, look for the minimum and maximum window width dimensions listed in the air conditioner's specifications and compare. Don't worry if the window AC does not extend to fit your window frame exactly. All window air conditioners come with installation kits, which include side curtains to seal off the extra space left on each side of the window opening.

  • Through-Wall Installation: If you plan to install a window air conditioner through your wall, first make sure the unit you want can accommodate this type of installation and that you have the appropriate installation kit. Then, make note of the dimensions of the finished wall opening, which should be listed in the Owner's Manual. Use these dimensions when creating your wall opening. If necessary, consult a professional when attempting to install your window AC through a wall.

Once it's completely installed — whether in a window or through a wall — the window air conditioner should sit level inside the opening, with the warm air exhaust system facing outside and the cool air return system facing inside. Some models, such as Friedrich window air conditioners, incorporate a slide-out chassis and rugged mounting sleeves that help stabilize each unit while giving you easy access for maintenance. Be sure to follow the manufacturer's installation instructions, which will be included with your unit.

Electrical Requirements — Window ACs are more powerful than other common household appliances. Because of this, you will need to make sure your existing electrical system meets the needs of the unit you choose. Most room air conditioners operate on 115-, 125-, or 220-volt circuits. Air conditioners that have cooling capacities below 15,000 BTUs usually run on 115- or 125-volt circuits. This is the norm for outlets in most bedrooms and living rooms. Window ACs with cooling capacities above 15,000 BTUs usually run on 220-volt circuits. With these models, you may need to install special electrical wiring or hire an electrician to do this for you. Electrical measurements — including voltage, amps, and watts — will be listed in an AC's specifications. Additionally, the correct plug face type may be pictured or listed by its National Electrical Manufacturers Association (NEMA) classification.

For example, the Friedrich Kuhl 9,700 BTU Window AC uses a "NEMA # 5-15P" plug type. This is a 125-volt/15-amp, 3-prong plug with a face that looks like this:


Along with the big three considerations of cooling capacity, installation type, and electrical requirements, there are a few other features you may want to consider:

  • Number of Fan Speeds — Many window air conditioners offer a choice of fan speeds for more flexibility in cooling and in noise level. A unit with at least two speeds is optimal.

  • Type of Controls — Do you prefer electronic or manual controls? You can often set a more accurate temperature and stick to it with an electronic thermostat and controls, since they allow you to toggle the setting to the exact degree. However, foolproof manual controls are easier to use than the sometimes-confusing electronic control panels, which may be packed with pushbuttons, LED screens, and indicator lights.

  • Noise Level — Today's window air conditioners are much quieter than legacy models. However, they will still make noise, so learn to expect it. As a strategy, think about how much noise you can withstand. Many models list their minimum and maximum decibel ratings in their product specifications. Most window AC decibel ratings fall around this measurement — give or take a few decibels — when operating on high.

Special Features

Along with the main window AC considerations, you'll find yourself weighing the benefits of many "nice-to-have" features as you peruse window AC models. These functionalities are in place to give you more control over your unit's operation and, in some cases, to boost operational efficiency.

Lots of window air conditioners are equipped with additional operating modes, making these models perform double- or even triple-duty in your environment. These can include fan-only settings for ventilation, independent heating modes, dehumidifier modes, and air purification modes. Most room air conditioners feature basic air filters that help remove large particles from incoming air that might otherwise get caught in the system and affect operation. These filters get more advanced at higher price points, and some may also remove odors and smoke as well as airborne germs. Mosquito traps are protective screens that work in the same manner, preventing mosquitoes and other bugs from entering the AC — and your room — from the outside.

To help direct airflow throughout your room, room air conditioners like the Friedrich Chill CP10G10A have adjustable louvers, which you can adjust horizontally and vertically to make air flow in multiple directions. This gives you better air circulation throughout your space. Programmable timers allow you to set timed operation and manage energy consumption. Remote controls give you the convenience of selecting and setting functions from a distance.

Eco-Friendly Refrigerants

In January 2010, the U.S. Environmental Protection Agency (EPA) began requiring air conditioner manufacturers to use eco-friendly refrigerants in their new air conditioner models, including central ACs, portable ACs, and window ACs. This decision is part of a larger program designed to protect the Earth's ozone layer by phasing out ozone-depleting HCFC (hydrochloroflourocarbon) refrigerants, which have contributed to significant ozone depletion over the South Pole.

One of the most common HCFC refrigerants used in air conditioners is HCFC-22, also known as R-22. The R-22 refrigerant has now been replaced by non-ozone-depleting R-410A refrigerant. All major AC manufacturers have begun using eco-friendly refrigerant in new AC models.

Safety and Security

Window air conditioner units have become safer to install and operate over the years with the introduction of sturdier window kits, electrical safety plugs, and current-protecting power cords. Be sure to follow the manufacturer's installation instructions closely when installing your window AC in a window or through a wall. If installed correctly, the AC unit should sit firmly and securely within the space without any opportunity for shifting. Often, you might need to use extra window brackets for sufficient support in your window. These can be purchased separately.

Safety becomes an issue when a window air conditioner is improperly secured or you use loose objects to support it. Setting objects on top of the housing is also discouraged. These objects may include things like bricks, wooden blocks, flower pots, satellite dishes, and/or birdfeeders. Safer current-protected electrical cords and polarized plugs drastically reduce the risk of electrical shocks during operation. Adding extension cords is not recommended.

To deter intruders, some window ACs are equipped with anti-intrusion protection systems. These systems are constructed of steel retaining wire that secures the chassis to the mounting sleeve in order to deter a "kick-in" intrusion.


Much like any other appliance, window air conditioners require periodic maintenance to keep them in top operating condition. These units are particularly susceptible to outside dirt and debris, which may accumulate inside the system as well as on the outside of it. Moreover, dust and other particles will build up on the air filter overtime, and animals and bugs might even nest near an AC unit. If these issues are ignored, they will reduce the overall effectiveness of your window AC.

To maintain effective and long-lasting operation, clean your window AC thoroughly at least once per year. Don't wait until you detect faulty operation. Window air conditioners that feature slide-out chassis make maintenance convenient because all you have to do is slide the unit out to access it. For maintenance tips and procedures, refer to your AC's owner's manual. Lots of times, all you have to do is use a vacuum crevice tool and a soft brush to sweep dust and dirt away from the internal components. Most air filters are easily washable with soap and water.

The Least You Should Know

  • When used to cool single rooms and small spaces, window air conditioners are effective alternatives to costly and inefficient central air conditioners.
  • A window AC's energy efficiency is indicated by its Energy Efficiency Ratio (EER) and Energy Star certification. For the most energy and cost-savings, look for units with an EER of 10.0 or higher and an Energy Star seal.
  • Consider three major points when shopping for a window AC: cooling capacity, installation type, and electrical requirements.
  • Other factors to consider include number of fan speeds, noise level, and type of controls. These depend mostly on personal preference.
  • Many room air conditioners offer special features to further simplify operation and boost efficiency. These include additional operating modes, advanced air filters, mosquito traps, programmable timers, remote controls, and adjustable airflow louvers.
  • Newer window AC models use eco-friendly refrigerants, such as R-410A, that will not deplete ozone, harming the environment.
  • Following the manufacturer's instructions will ensure that you install your window AC properly, so that it is stable and secure. Never sit anything on top of your unit. Use extra brackets if necessary to increase support, and do not use an extension cord.
  • To properly maintain your window AC, clean it thoroughly at least once per year using the manufacturer's instructions as a guide. Don't wait until you detect faulty operation.

Still Have Questions?

For more information on specific window air conditioners and other ways to improve your indoor air, browse our products and visit our Knowledge Center. Not sure what's best for you? We can take the guesswork out of decision-making. Contact our product experts toll-free at 1-800-934-9194. We want to help make your indoor environment healthy and comfortable.

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