What's a BTU? Solving the A/C mystery once and for all!

Every summer, I tell myself I need to get an air conditioner. But then somehow it always ends up being the middle of the summer, by which time I’ve become content with sleeping with ice packs and eating 100 boxes of freezies, and I just can’t justify buying one. But this year, my boyfriend had had it and with an impending heat wave, there we were, wandering through Wal-Mart with my sister, deciding on an air conditioner. “What about this one, this one is fine I’m sure,” I asked, pointing to a cheap one that looked decent enough to me. “No way man, that’s only got like 5,000 BTUs,” my sister told me. We both burst into laughter after she said it because obviously I had no idea what “BTU” meant and my sister’s house is currently a sauna and she has no plan for a/c in her near future. As it turns out, though, nobody really seems to know what BTU means.

What exactly is a BTU?

BTU is short for British thermal unit. In an air conditioner’s case, it describes the amount of energy needed to cool one pound of water by one degree Fahrenheit.

So what exactly does that mean?

Essentially it means that the higher the BTU capacity, the higher the cooling capacity of your air conditioner. It seems obvious to get one with the most BTUs per hour, but in fact, it’s not. If you buy one that is too strong for your room, you’ll freeze (and waste energy) and if you buy one that isn’t strong enough, it won’t cool the area (and again you’ll waste energy). Generally speaking, you can rely on the size of the area you want to cool to guide you:

AC story

Table by Energy Star

There are a few exceptions to look out for though.

Click on the snowflakes to find out more:

Another acronym to look out for is EER, which stands for energy efficiency rating. This rating tells you how much electricity is used to produce cool air. The higher the EER, the more energy efficient your unit will be. These units tend to be more expensive, but can save you money on your energy bills.

If you’re having trouble deciding between two air conditioners with the same BTU capacity, checking the EER can help you out.

In the end, I bought an air conditioner with 5,000 BTUs per hour, and it’s now nestled comfortably(ish) in my living room window and doing a great job cooling the space. The cool air even creeps into the kitchen and bedroom. My apartment is about 600 sq. ft. and we figured the living room was probably about 150 sq. ft., so this unit was perfect for us. Now we just spend a lot of time in the living room.

Click here for tips on staying cool during a heat wave.

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