Indoor air conditioning is one of the best ways to beat the summer heat. For many, the convenience of central air remains out of reach, which leaves the window AC unit as the next best thing. 

Today’s window air conditioners are much better than what you might be used to, and nothing like the massive energy hogs they once were. Modern window units provide relief from searing temperatures, remove humidity and use less electricity than ever before. 

However, if you don’t do your homework, it’s easy to end up with the wrong machine. You might get stuck with something too big, too small or that simply doesn’t fit where you want.

What Size Air Conditioner Do You Need?

The Rules for Keeping Cool

Window air conditioners typically have a cooling capacity ranging from 5,000 to 12,500 British thermal units (Btu/hr.). As a rule of thumb, an air conditioner needs 20 Btu for each square foot of living space.

But other considerations, such as the ceiling height and the size of your windows and doorways, might call for more cooling power.

To measure your room, multiply the length by the width. Add together the size of rooms that aren’t separated by doors, because the air conditioner will need to cool both spaces. Energy Star recommends that you make adjustments for the following circumstances:

• If the room is heavily shaded, reduce capacity by 10 percent.
• If the room is very sunny, increase capacity by 10 percent.
• If more than two people regularly occupy the room, add 600 Btu for each additional person.
• If the unit is used in a kitchen, increase capacity by 4,000 Btu.