What Size Air Conditioner Do I Need? How to Pick the Right BTUs

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I’m a huge baby about temperature, and fans sometimes just don’t cut it. So in the midst of a recent heatwave I decided I was going to bite the bullet and get an air conditioner. But when I started researching online, I found myself confused by the various units’ cooling and efficiency numbers, with prices seemingly directly correlated with each. I didn’t really know what any of them meant. Given the size of my apartment, how big of an air conditioner did I need?

“Many people buy an air conditioner that is too large, thinking it will provide better cooling. However, an oversized air conditioner is actually less effective—and wastes energy at the same time,” explains the very helpful Energy Star website. “Air conditioners remove both heat and humidity from the air. If the unit is too large, it will cool the room quickly, but only remove some of the humidity. This leaves the room with a damp, clammy feeling. A properly sized unit will remove humidity effectively as it cools.”

But before you run out and snag a small air conditioner, there are several factors worth considering, and a few vocab words that’ll make shopping for an A/C so much easier. For starters, you’ve most likely seen the letters “BTU” that seem to appear in every unit’s description after sets of numbers. You’re also probably wondering how to properly measure your room for an air conditioner, it’s not exactly as simple as measuring for a new couch. It’s these types of questions that make you wonder why they don’t teach these things in school. But I’ve got some helpful information on these topics, so you can be as cool as an ice cube during the most sweltering months.

BTU stands for British Thermal Unit, and it measures the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. According to the U.S. Energy Information Administration (EIA), one BTU is about the same amount of energy you’d get from burning a match. You’ll use this form of measurement to match up with how much square footage is in your room, but more on that below. It sounds oddly specific (and yeah, the name’s a little weird), but knowing what BTUs are will help you find an A/C unit that’s optimal for your space. 

How do I calculate the right size air conditioner?

There are a variety of variables that go into selecting the air conditioner worth spending your money on. One of the most important factors for calculating the right size unit is determining how big your room is. Consumer Reports recommends having 20 BTUs per square foot of the living space (or spaces) you’re wanting to cool down. But no worries about having to do any confusing equations—luckily there’s a convenient chart for figuring how much A/C power one needs for a room.

Area To Be Cooled (sq. feet)

→ Capacity Needed (BTUs per hour)

My air conditioner was for my living room, so I measured the room with a handy tape measure. It’s not the most exact measurement in the world, but it’s close enough. My living room is roughly 330 square feet, which the chart tells me means I need an AC unit with a capacity of 8,000 BTUs per hour — which was way less than I expected.

Of course, a room’s environment doesn’t just depend upon square footage. In some cases there might be environmental issues to be aware of. For example, in very sunny rooms, you should increase the necessary capacity of an air conditioner by 10 percent. For very shady rooms, decrease it by 10 percent.

If there are often more than two people in the room, add 600 BTUs per person, or make them bring ice. If you are cooling the kitchen, remember that ovens and stovetops put out a lot of heat, and your A/C will have to compensate. Add 4,000 BTUs for any unit you install in this room. The last thing you should consider? What type of A/C unit will serve your room best.

Is a wall-through unit the same as a window unit?

Nope, these two styles of A/C are very different. If central air isn’t already built into your place, there are several other options like portable air conditioners, but two of the most common being wall-through and window units. A wall-through A/C is a permanent fixture that’s added to a wall, oftentimes in a room that doesn’t have windows. If your apartment doesn’t already have one, this option is usually better reserved for homes, because it typically requires a pro to step in for installation. Window units on the other hand can be easily added and removed and do exactly what their name implies: cool you down from the comfort of one of your windows.

Now for the fun part! To help you get started, we’ve compiled a list of the best rated air conditioners that’ll help you keep your space refreshingly cool. Our picks include:


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