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5 Things to Consider When Buying a Window Air Conditioner

5 Things To Consider When Buying A Window Air Conditioner

Window air conditioners, like portable air conditioners, are designed to cool single rooms or–with enough BTU power–a few rooms at a time. Also known as room air conditioners, window AC units are self-contained appliances that house all the components needed to cool an area in one tidy package. Traditionally, these units are installed inside standard double-hung windows. However, many models on the market today can also fit inside an appropriately sized wall opening.

There are many things to consider when shopping for a window air conditioner. For instance, what size should you get? How much maintenance is required? And probably top of mind–how is it installed? To get answers to these questions and more, here are 5 things to consider when shopping for a window AC.

1. Cooling Capacity

When shopping for the right window air conditioner for your space, make cooling capacity your first consideration. Cooling power is measured in British Thermal Units, or BTUs, per hour–the basic measure of thermal energy. For the best efficiency and effectiveness, stick with a unit that has a BTU level designed to fit your space. After all, a window AC with too little BTU power will run continuously to try to cool a large space and, in the process, will eat up your energy budget. A window AC that is too large for your space will not cool and dehumidify your space evenly, leaving your room air susceptible to uncomfortable hot and cold pockets.

To find your ideal cooling capacity, calculate the size of the space you want cooled in square feet. Then use the chart below to find the right amount of BTUs.

Area To Be Cooled (Sq. Ft.)

Capacity Needed (BTUs Per Hour)

100 to 150 sq. ft.

5,000 BTUs

150 to 250 sq. ft.

6,000 BTUs

250 to 300 sq. ft.

7,000 BTUs

300 to 350 sq. ft.

8,000 BTUs

350 to 400 sq. ft.

9,000 BTUs

400 to 450 sq. ft.

10,000 BTUs

450 to 550 sq. ft.

12,000 BTUs

550 to 700 sq. ft.

14,000 BTUs

700 to 1,000 sq. ft.

18,000 BTUs

1,000 to 1,200 sq. ft.

21,000 BTUs

1,200 to 1,400 sq. ft.

23,000 BTUs


For a more detailed estimate, take these factors into consideration, too:

  • Ceiling Height — The estimates above assume traditional 8-ft. ceiling heights. You may want to increase your BTU level if your ceilings are higher than 8 ft.
  • Sunlight — Is your room sunny during the day? If so, increase your BTU power by 10 percent.
  • Shade — If your room is heavily shaded throughout the day, you can decrease the BTU power by 10 percent.
  • Number of People — Will more than 2 people regularly occupy the room? For each additional person, you'll need 600 BTUs of cooling capacity.
  • Kitchen — Will you be installing the unit in a kitchen? If so, increase the capacity by 4,000 BTUs.

2. Installation

Next, you'll need to consider where you will install the unit. Most window AC models are designed to fit inside double-hung windows. However, many of these models can also be installed inside a custom-created wall space with special mounting hardware. This is a useful alternative if your window's dimensions are too small or too large, if you don't have vertical sash windows, and if you're willing perform the extra work necessary to create a wall opening.

When completely installed–whether in a window or through a wall–the window air conditioner will sit level inside the opening, with the warm air exhaust system facing outside and the cooling system facing inside. In addition, many window air conditioners feature a slide-out chassis and a rugged mounting sleeve that work to stabilize and secure the unit, while giving you easy access to it for maintenance. For reliable reference, all window air conditioners also come with detailed, easy-to-follow instructions for installation.

If you will be installing your unit inside a window, measure the dimensions inside the window frame exactly, paying special attention to the width. Then, 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 a window or wall opening.

If you will be installing your window air conditioner through a 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 product's specifications. Use these dimensions for the wall opening. If necessary, consult a professional when attempting to install your window AC through a wall.

3. Electrical Requirements

Because window air conditioners are more powerful than other common household appliances, you'll need to make sure that your existing electrical system meets the needs of the unit's electrical requirements. Most room air conditioners operate on 115-, 125- or 220-volt circuits. Units that have cooling capacities below 15,000 BTUs usually run on 115- or 125-volt circuits. This is the norm for 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 seek out an electrician to do this for you.

Electrical requirements–including voltage, amps, and watts–will be listed in a unit's specifications. In addition, the correct plug face type may be pictured or listed by its NEMA (National Electrical Manufacturers Association) classification.

For example, the Friedrich YS10M10 9,500-BTU Window Air Conditioner air conditioner uses a "NEMA # 5-15P" plug type. This is a 125-volt/15-amp, 3-prong plug with face that looks like this:


4. Energy Efficiency

In general, window air conditioners are a more economical choice than central air conditioners. They cost less to purchase and–if sized correctly for a space–are cheaper to operate over the long-term. To gauge a unit's energy efficiency, look for two things in the product's specifications: an Energy Star rating and/or an EER number.

Energy Star-rated room air conditioners use approximately 10 percent less energy than traditional models. These units also have extra features that give you better control over operation and energy output. These include programmable timers, digital thermostats, and multiple cooling speeds to choose from.

Another way you can determine a window AC's level of efficiency is by looking at its EER, or Energy Efficiency Ratio. An EER measurement tells you how many BTUs the unit uses for each watt of power. Use this as a rule of thumb: the higher the EER, the more efficient the air conditioner. According to the U.S. Department of Energy, you should shop for a room air conditioner that has an EER of at least 10.0 to realize the best energy- and cost-savings. Window air conditioners by Friedrich and Sunpentown are known for both their high EERs and Energy Star-qualified operation.

5. Maintenance

Like any other appliance, window air conditioners require periodic maintenance to keep them in top cooling condition. These appliances are particularly vulnerable to outside dirt and debris, which can accumulate inside the unit as well as on the back of the unit. In addition, dust and particles will build up on the unit's air filter overtime, and animals and bugs may even nest in or near it. If left untreated, all of these things will eventually combine to reduce the effectiveness of your air conditioner.

To ensure effective and long-lasting operation, clean your unit thoroughly at least once per year. Don't wait until you detect faulty operation. Window ACs with slide-out chassis make this routine convenient because all you have to do is slide the unit out to access it. For maintenance tips and instructions, refer to your unit's owner's manual. Most of the time, all you need to use is a vacuum crevice tool and a soft brush to sweep away dust and dirt from internal components. Most air filters are washable with mild soap and water.

For protection from pests, some room ACs–like the Friedrich Kuhl Series Ultra Premium models–are equipped with mosquito traps that allow condensation to flow outside without letting insects inside.

Of course, these 5 things aren't the only ones you should consider before buying a window air conditioner. They are, however, the most influential factors that affect a window AC's long-term operation. Other things you may want to consider deal mainly with your personal preference. These can include noise level, type of controls, number of fan speeds, additional operating modes, and safety features.

Still Have Questions?

For more information on specific products and ways to improve your indoor environment, review our extensive product listings and other educational materials. Not sure what’s best for you? We can take the guess work out of decision-making. Contact our product experts toll free at 1 (800) 934-9194. We want to help you make your indoor environment a healthy one.

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