How To Calculate How Much AC Power You Need

How To Calculate How Much AC Power You Need

Joelle Alcaidinho
Jun 27, 2012

After spending another sweltering weekend in my flat I knew it was time to replace the once-trusty window AC unit that had become not-so-trustyworthy. As I began a search for a replacement I tried to figure out just how many BTUs I needed for the space, wondering whether I needed an upgrade...

When shopping for AC, in addition to the guidelines that Energy Star puts out (as shown in the chart above) there are a few other important things to consider:

1. The Shape of the Space: What kind of space are you looking to cool? In addition to looking at the total square footage you want to consider at how the space is laid out and if it contains any heat sources like an oven. In our railroad style flat, in order for the bedroom to be cool, the air would have to travel past the hot kitchen which means that a more powerful unit is required.

2. The Amount of Sunlight: Are you trying to cool a space with large windows that let in lots of sunny heat? Best to get some shades to block some of that sun and factor the windows into your AC buying decision. A very sunny room requires the AC to work 10% harder to maintain the same level of cool.

3. Will the Cold Air Escape? Just as you would think about heat escaping in the winter, make sure to seal up any places where the cool air can escape. You don't want to spend money cooling the outside! A home that's not well insulated will take more AC to cool.

4. How Many People Will be in the Room? If you are looking for an AC for your room in which you host lots of gatherings thing about that when you're calculating how much AC you need. For rooms with more than 2 people regularly in them Energy Star suggests calculating an additional need of 600 BTUs per person.

5. Let Fans do Some Work: Properly placed oscillating fans can help cut down on how hard an AC needs to work to cool the room. Pick up some inexpensive fans and use them in the corners to help the cool air to circulate and you'll need less BTUs for those spaces that are a bit awkward to cool.

In the end, I settled for an AC that was slightly less BTUs then recommended by Energy Star and did my best to help the air to circulate with the help of some strategically placed fans. The new AC seems to be working out pretty well and and I'm quite happy I didn't wait till July to install it!

(Images: 1, 3. Flickr members Brendon and Stefani Seskin licensed for use under Creative Commons, 2. Energy Star )

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