Here are some terms you’ll find when shopping for window treatments, and some additional tips after our years of testing.
BTU stands for British Thermal Units. In the case of air conditioning, BTU is a way of measuring how much heat a compressor can remove from a room. There is a quick and easy way to find out if the AC unit is capable of cooling your space. First, you’ll need to find the square footage of your room by multiplying the length by the width. Then, use the US Department of Energy’s guidelines for the BTU capacity you need. For example, a 150 to 250-square-foot room may need a 6,000 BTU AC unit or higher for proper cooling.
See Integrated Energy-Efficiency Ratio (CEER). You should list a CEER rating on any air conditioner you buy, which is one of the best ways to check the energy efficiency of a unit. You will see a number between 9 and 15. The higher the number, the lower the cost when the electricity bill arrives. A small window AC unit may save you money initially, but it may end up being much cleaner in the long run. The US Energy Star program has a website where you can check AC units based on their CEER rating.
Check local laws. Some cities, such as New York City, require brackets to be installed to support your window AC. Something as simple as this example should do the job, although we haven’t tried it yet. You may want to go to the hardware store for some plywood to make sure your window screen is flat, but that depends on the type of windows you have and the model of AC you buy. When installing, ask a friend to help you. These units are heavy and difficult to hold, the last thing you want is to drop one out the window.
Measure your window. Before you buy, read the supported window types and sizes for the AC unit you’re looking at, and measure your window to be safe. Be sure to seal as many places as you can with the included foam (you can buy more if you want).
Correction July 28, 2021: It has been clarified that BTU measures the amount of heat that can be removed, not the amount of energy required to remove the heat. Thanks, readers.