How to prevent your window AC unit from falling out, and other cool tips

It's time to get that air conditioner going again.
One side of a reddish-brown brick building, with 15 windows arranged in a grid on the façade, each containing a separate window air conditioning unit.

Some of these window units are installed safely, with support brackets, and others are liable to plummet to the concrete below. Thomas Layland/Unsplash

A heat wave has been scorching the US, signaling that summer weather is upon us. And if you’re part of the quarter of Americans reliant on individual air conditioners (versus built-in central air), that probably means it’s time for the annual struggle of installing a window unit.

But before you muscle that bulky old thing into position, take a few minutes to read this guide. We think you’ll come away with a bunch of good tips that will make living with this seasonal technology a breeze.

Make sure you have the right unit for your home

There are lots and lots of window unit options available (an Amazon search for “window unit air conditioner” yields more than 800 results). That can be intimidating for anyone looking to buy a new air conditioner or considering an upgrade.

[Related: Best air conditioners]

First, think about size. If your unit is too small, you’re less likely to maintain a sweat-free space. On the other hand, if it’s too big, you’re forcing the machine to operate inefficiently, says Joanna Mauer, senior research manager of the Appliance Standards Awareness Project at the American Council for an Energy Efficient Economy. Although larger units can cool a space more quickly, they end up frequently turning themselves on and off in small rooms while trying to maintain a set temperature, she explains. Frequent on-off cycling makes a window unit work harder and also lowers its ability to take moisture out of the air (or dehumidify), which is an important step in making a room feel habitable in the summer swelter.

Contrary to what you might think, the measurement that matters most is not height, width, or weight. No, you should be paying attention to British thermal units (Btu) per hour. This unit indicates how much heat an air conditioner can remove from a space over the course of an hour. Generally, you need 20 Btu per hour for every square foot of space.

Energy efficiency matters too—for your wallet and the environment. Air conditioners are energy-heavy appliances, and while there are some ways to reduce energy costs on your own (more on that later), it’s easier if you have a unit that uses less energy from the start. Don’t just take our word for it: The US Department of Energy estimates that a mid-sized (8,000 Btu per hour) window AC unit consumes more energy in one year than a new refrigerator—even accounting for the months most don’t use AC at all, says Mauer.

That means air conditioning can account for more than half of a city’s electricity usage on a blazing summer day, says Forrest Meggers, an engineer and assistant professor at Princeton University’s Andlinger Center for Energy and the Environment

[Related: How to build a house that doesn’t need AC]

To spend less on energy, look for Energy Star-rated window units, which can save you about 10 percent on your energy bill, says Mauer. Or, even better, units labeled “Energy Star Most Efficient,” which use a type of compressor technology that allows the cooling component within an AC unit to run at a more optimal level.

Choose the right location

When installing your air conditioner, it also pays to carefully consider the unit’s placement. If you have multiple windows to choose from, it’s best to pick one that faces north or east, which will generally get less direct sun exposure than one facing south or west, says Meggers. Putting your unit in the shadiest window possible boosts AC performance. “If it gets hit by the sun, that makes [your unit] have to work harder to get rid of its heat,” Meggers says. “And that just means more electricity for the same amount of cooling.”

Learn the safest way to install a window AC unit

One of the biggest dangers with window AC units is the risk that they’ll fall out and potentially kill someone below. Whether you bought a new unit or not, it’s important to make sure you install it correctly and safely every time. The best way to do that is to have a friend help, says Howard Lupowitz, owner of Mike’s Air Conditioning and Air Vent Medics in New York City. Window AC units average 64 pounds and can go up to 130, so maneuvering one into place is rarely a one-person job.

Lupowitz recommends installing a metal bracket to support your unit, and points out that brackets are required by New York City law in multi-dwelling buildings of six stories or taller. These brackets fasten to the outside of the window frame, securing the AC unit and preventing catastrophic falls. Lupowitz says installing this kind of support is often the most difficult part of the process because it requires power tools and lengthy screws, but it’s critical nonetheless. A simple brick underneath the exterior side of an AC unit won’t cut it, he says, both for safety and for making sure your unit is set at the recommended angle (usually tilted slightly down to the outside).

Maintain your chill

Tilting your unit is important because as it cools the air, it pulls moisture out of it. That vapor then condenses inside the machine. If you installed your air conditioner correctly, this condensation will drain out the back, as opposed to pooling inside. Stagnant water is bad for your windowsill, your window unit, and potentially your indoor air quality.

More than simply making things wet, excess moisture turns the inside of a window AC unit into the perfect place for hidden mold growth, which means the air blowing into your home could be chock-full of irritating (and potentially toxic) spores. It’s even possible to become allergic to your air conditioner if you don’t install and maintain it properly, says Lupowitz.

To check for mold, shine a flashlight into the top vent of your AC unit (where the cold air comes out) and look for patterns of dark specks, particularly on any foam insulation. Once mold moves in, it can be extremely difficult to remove completely, and proper cleaning requires dismantling and reassembling the machine. Sometimes, Lupowitz says, professionals like him will help—but it’s often not worth the trouble. 

[Related: Why does mold come in so many colors?]

To prevent the problem in the first place, he suggests spraying a 50 percent white vinegar solution into your AC unit, which will kill spores before visible mold shows up. Routinely cleaning your AC’s removable air filter will also help prevent mold growth, and it’s easy to do. All window ACs should have removable filters that are accessible from inside your home. But because the process varies depending on the model, we can’t cover every step here—check your owner’s manual for details. Lupowitz recommends wiping down the filter every two to three weeks to remove dust. Plus, keeping the filter clean will also make your unit more efficient.

Get the most bang for your buck

So, you’ve got the best window AC unit, you’ve installed it correctly, and you’re routinely cleaning the filter and spraying for spores. What else can you do to try to lower the cost of chilling your home all summer?

Time of day and outdoor temperature both change the efficiency of your unit, so you can optimize efficiency by running it in the early morning when the air is still cool, Meggers says. Then, once your room has become “over-cooled” and the sun has hit its peak, you can give the AC a rest. This may seem counterintuitive, but cooling your inside air before it can heat up means that your machine works less to keep your home at a comfortable temperature. 

And it may seem obvious, but one of the best ways to efficiently use a window unit is to take advantage of the “off” switch. With central air, you have to cool the whole home to chill a single room. However, window units can turn down the temperature of the room they’re in and avoid putting energy into cooling a space you’re not using. “There is a pretty big performance gain when you turn off your air conditioner in your bedroom during the day and turn on the window air conditioner downstairs,” says Meggers. “You’re basically cutting in half your cooling demand.”

Finally, staying cool in the summer isn’t just about the number on your indoor thermostat. 

“Comfort is just managing the heat that’s leaving your body,” Meggers explains. If moisture is evaporating off your skin or heat moves away from you as you produce it, you will feel cooler. Changing the temperature inside your home with AC is one way to help with that, but humidity and air circulation also play a big role. Fans are your friends, he says. Ceiling fans, desk fans, box fans—all can help your body cool down while using much less energy than a window unit.     

That said, AC is sometimes a necessity for your comfort and health when fans aren’t enough. We just want what’s best for you, and this summer that’s a clean, efficient air conditioner that stays in place and doesn’t blow through your bank account. Spend that money on your favorite summer treat instead.