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Air Conditioner Sizing

What sized air conditioner do I need?

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Air conditioners at supermarket Yamini Chao/Digital Vision/Getty Images

Air conditioners come in many different sizes, whether they are window air conditioners or central air conditioners. These units should be sized to cool the area of your home you’re trying to cool with the most efficiency. So how do you do that? Well, by measuring the area of the area to be cooled, you’ll have a pretty good idea what size air conditioner is for you.

To calculate this, simply multiply the length times the width of the room or area to be cooled. Then, as a practical number, multiply that total times 25 BTU. This allows ample cooling, whether it is a rainy, moist day or a hot, sunny, humid day. Let’s say the room is 12 feet wide by 15 feet long. That means 12x15=180 square feet. Take the 180 sq. ft. times 25 BTU per square foot and you get the minimum BTU air conditioner you should buy. That means 180x25=4500 BTU cooling capacity is needed.

You may ask if a smaller air conditioner will work or a larger one may be better? Here’s a thought about those questions. Smaller BTU units will continually run, just trying to keep up. This will increase your electric bill and it is unlikely the unit will be able to cool the area effectively.

An air conditioner too large can be overkill. To dispute the rumor that bigger is better, an air conditioner too large will cool more quickly, but that may impede the reason for running the air conditioner in the first place. You see, along with cooling the air, the air conditioner is also extracting moisture from the air (humidity) that makes all of us feel hot and sticky. Although the air may be cooler, if the unit doesn’t run long enough, the moisture cannot be extracted from the air properly. It would be like being outside camping on a cool, clammy, foggy night. You know the feeling when your skin is moist and you get goose bumps when cool air flows over it. Besides, an air conditioner too large will cycle on and off frequently.

Do yourself a favor and measure the area of the home to be cooled, calculate your BTU needs and size the air conditioner properly. Your local appliance store or heating and cooling center can aid you in selecting the proper air conditioner size for your home. Remember, too little is never enough and too much of a good thing can be bad.

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