Find the Right Size Window Air Conditioner for Every Room

Room Sizes and BTUs

Window air conditioner unit set at 70 F.

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When it is a time for air conditioning in the heat of summer, knowing which type of air conditioner to buy makes all the difference. You may need a whole-house central air conditioner, a portable air conditioner, a built-in wall-mounted air conditioner, or simply a window air conditioner. Then you need to know which type of AC unit you need, depending upon the outlet available to feed it. It may be a 120-volt model that is most common or a 240-volt model, which is usually larger in size and more efficient as it runs. However, this may not be true as this option often cools a much larger area than that of the smaller 120-volt models.

If it's time for a new window air conditioner, but you don't know what size you need, this chart will be helpful. Air conditioners are rated by BTUs, and their cooling capacity is directly related to the number attached to this BTU symbol. The larger the BTUs, the greater the cooling capacity. By using the chart provided, you'll have a good idea of the minimum sized air conditioner to utilize for cooling in your room or areas of the home.

Then again, the window air conditioner that you choose may be no more than supplemental cooling for a specific room in your home. You can add a window air conditioner in the bedroom for nighttime cooling. You can use it in addition to the central air, which keeps the entire house comfortable, but not necessarily overly cool, as per the setting. If you want to add a little cooler environment to the bedroom, fire up the energy-saving window air conditioner to cool that room a bit more to make sleeping more comfortable.

Physical Size and Shape

The physical size of the window air conditioner can be related to cooling capacity. In other words, small window air conditioners often have smaller BTU ratings, while larger BTU capacity often translates to a larger unit. This may become a problem when the right size of window air conditioner—when measured by BTUs—won't fit inside the window opening. If a small window forces you to choose a smaller unit than you need, consider using a second air conditioner in another window in the room.

To measure a window's size, open the window as far as it will go, then measure the height and width of the window opening. This is the maximum size of the air conditioner that the window can accommodate. Finally, note the window's configuration. Most window air conditioners are designed for single-hung or double-hung windows. If you have a sliding window (slides side-to-side), make sure the air conditioner you choose is compatible with sliding windows. Some units require external support to work with sliding windows.

Matching the Circuit Size and Outlet Type

The next thing to consider when sizing a window air conditioner is the electrical outlet near the window where you're going to install the unit. Window air conditioners come in both 120- and 240-volt models. Each requires a different electrical outlet, so be sure to check that out in advance of purchasing the unit or you may need to rewire and an outlet for the unit.

Air Conditioner Sizes

The table below lists the square footage of the room and the required BTUs needed to sufficiently cool the room. This gives an indication of the size unit that will run the most efficiently, without overworking the air conditioner on those hot days.

Btu Rating                Square Feet of Cooling
5,000 Less Than 150
6,000 150225
7,000 225300
8,000 300350
10,000 350500
12,000 500650
14,000 650875
18,000 8751,100
21,000 1,1001,300
25,000 1,3001,600
29,000 More Than 1,600