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How to choose a cool AC window unit

What you need to know to buy the right window air conditioner.

Tyler Lizenby/CNET

Indoor air conditioning is one of the best ways to beat the summer heat. For many, the convenience of central air remains out of reach, which leaves the AC window unit as the next best thing.

Today's window models are much better than what you might be used to, and nothing like the massive energy hogs they once were. Modern AC window units provide relief from searing temperatures, remove humidity, and use less electricity than ever before.

However, if you don't do your homework, it's easy to end up with the wrong machine. You might get stuck with something too big, too small, or that simply doesn't fit where you want. Read on to learn how to avoid these pitfalls.

Know before you buy

Deciding on an air conditioner depends on a few key factors. Here is list of details you should figure out before you shop.

  • Target coverage area in square feet (or square meters)
  • Size and shape of your windows
  • Where to channel the water from condensation
  • Position and voltage of nearby electrical outlets

Calculate your coverage area

First, you need to figure out how big an area you plan to keep cool. That could be a standard-size bedroom, a living room or even an entire studio apartment. Regardless, add up the total square footage that your AC unit will tackle. Then use that number to select the right power output and cooling capacity. The EPA (Environmental Protection Agency) Energy Star website has a handy tool for this.

Say you live in a small studio apartment (700 to 1,000 sq. ft. or 65 to 92 sq. m.). An air conditioner with a BTU (British Thermal Units) rating of 18,000 fits the bill. An average family room (300 sq. ft or 27 sq. m.) requires a 8,000 BTU AC unit. If what you're after is cooling down a 250 sq. ft. (23 sq. m.) bedroom, then look to an air conditioner with a 6,000 BTU etc.

The EPA (Environmental Protection Agency) Energy Star website has a handy tool for calculating the right size AC unit you need.

EPA Energy Star

Measure your windows

Typically, window-mounted AC units are exactly that. The body of the appliance sits partially inside and partially outside of the window pane. A bracket or brace of some sort holds the air conditioner in place. This bracket also divides the inside from the outside, and hot air from cool air.

Since there's no universal standard for window size, measuring your window dimensions is a must. Once you have that info, you can then compare it against the specifications of any potential new machine. This way you'll hopefully avoid any nasty surprises when it's time to install.  

Permanent or temporary use

Decide if you plan to remove your new air conditioner at the end of summer, or leave it in the window year-round. There are trade-offs to either approach. With a permanent setup, you don't have to reinstall your air conditioner each year.

Even if your permanent AC mount is well-insulated, though, it won't be as draft-free as a quality window that's completely shut. That can be a problem if you live in a place with near- or below-freezing temperatures in the winter. If you live somewhere with mild winters, you should be just fine.

A portable air conditioner represents a third option. These free-standing appliances cost more than their window-style siblings, but move easily from room to room since they come with wheels. You need to mount an exhaust hose assembly inside your window, but the hose hardware is lightweight and installs much more easily than whole in-window AC unit.

Think about condensation

One downside to air-conditioned comfort is condensation. Similar to dehumidifiers, AC units pull moisture from the air as they run. That collected water must go somewhere, usually pooling in an internal drip tray. Some AC models advise you to drill a small hole in them for drainage. You can then hook a drain hose there, to channel excess water toward wherever you want it to go.

Electricity and power

Decades ago, it wasn't uncommon for old air conditioners to need high-voltage (240V) electrical outlets. Thanks to Energy Star certification, current models are a lot more efficient. They can operate at 120V, the default voltage for US home appliances.

It's a good idea to check the situation in your particular home. A legacy, defunct AC unit may only have a 240V outlet nearby. Here's another problem you might run into. The closest outlet is 120V, but it shares a circuit with other power-hungry appliances or electronics. In either scenario, you may have to have an electrician make repairs or add extra circuits.

GE has a line of window air conditioners that come with smart features, too.

GE Appliances

Sweat the small stuff

Features beyond size and cooling power might seem minor, but they can have a meaningful impact on how you use a window AC unit. Many AC units can make unholy racket when running, so be sure to check the noise rating of whichever models you're considering.

Smart features have started to appear on some air conditioners, too. Frigidaire and GE now offers both window AC and portable AC units that give you control through a mobile phone app. GE also sells a line of connected window air conditioners. You can set schedules for them, and sync settings across multiple units so they act like one, joined cooling system. 

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