The Most Efficient Way to Run Your Window Unit

By Michael Franco

June 12, 2025

The Most Efficient Way to Run Your Window Unit

Window air conditioners can be lifesavers during the hot summer months, especially in older homes or apartments without central air.

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But while they offer targeted cooling, they can also drive up your energy bill fast if they’re not used efficiently. The good news? A few smart strategies can keep your space cool and your costs low.

Start With the Right Size Unit

Efficiency starts before you even hit the power button. If your window unit is too small, it’ll run constantly and still leave you sweating. Too big, and it’ll short-cycle — cooling the air quickly but not running long enough to properly remove humidity. That results in a clammy, uncomfortable environment and wasted energy.

To find the right size, look at the unit’s BTU rating. “BTU” stands for British Thermal Units. For example, a 150- to 250-square-foot room generally needs a unit with about 6,000 BTUs, while a 350- to 450-square-foot room may need 10,000 BTUs. Energy Star has helpful guides for selecting the right size based on room dimensions, insulation and sun exposure.

Set It and (Mostly) Forget It

The sweet spot for both comfort and efficiency is to set your thermostat at about 78°F (25.5°C) when you’re home. This is the recommended setting from the U.S. Department of Energy — cool enough to feel comfortable, but not so low that your unit is working overtime.

When you leave the house, you can bump the temperature up by 5 to 7 degrees, especially if no one is home. If your window unit doesn’t have a built-in timer or smart controls, consider plugging it into a smart outlet or external timer so it can automatically power down and back up based on your schedule.

Use ‘Eco’ Mode — Yes, It Really Helps

Most newer window air conditioners come with an “Eco” or “Energy-Saver” mode. Unlike the standard cooling setting, which keeps the fan running continuously, Eco mode cycles the fan on and off along with the compressor. When the room reaches your desired temperature, the whole unit shuts off and only comes back on when the temperature rises again.

This setting is more energy-efficient than leaving the fan running nonstop. While it might feel a bit less consistent in terms of airflow, it can significantly cut down on electricity use without sacrificing overall comfort.

Don’t Neglect Air Circulation

Ceiling or oscillating fans are a perfect companion to your window AC. Fans help distribute cool air throughout the room, reducing the need to crank the AC lower than necessary. Since fans use far less energy than an air conditioner, you can often raise the thermostat setting a few degrees and still feel just as comfortable.

Also, make sure your furniture isn’t blocking airflow from the unit. If it’s tucked behind a curtain, sofa or shelf, that cooled air may not reach the center of the room, causing the AC to work harder.

Keep Doors and Windows Sealed

Even the best air conditioner will struggle if you’re losing cool air through gaps or pulling in hot air from outside. Check for drafts around your unit and window frame. Use foam insulation or weatherstripping to seal any leaks and keep the cold air in.

And while it may seem obvious, always keep doors and windows closed when the unit is running. Otherwise, your AC is trying to cool an ever-expanding space, which is a fast track to high energy bills.

Clean or Replace the Filter Regularly

One of the biggest factors affecting your window unit’s performance is a dirty air filter. A clogged filter forces the unit to work harder to pull in air, reducing its cooling efficiency and potentially damaging internal components.

During peak summer use, check and clean the filter every two weeks. Most filters can be rinsed under warm water and dried before reinserting. If your model uses replaceable filters, make sure to change them as directed — typically every one to two months.

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Close Curtains and Blinds During the Day

Sunlight streaming through your windows might look pretty, but it’s also heating up your room and making your AC work harder. Block out the sun with blackout curtains, reflective shades or even just tightly closed blinds, especially on south- and west-facing windows.

This simple trick can reduce indoor heat gain by as much as 33%, giving your window unit a much easier job.

Upgrade to an Energy Star Model

If your unit is more than 10 years old, it might be time for an upgrade. Newer models with the Energy Star label are certified to use less energy while delivering the same cooling power. Some also come with smart features that let you control them from your phone and automatically adjust to save power when you’re not home.

You may also be eligible for rebates or energy-saving incentives through your utility provider or local government when you upgrade to a more efficient model.

Don’t Cool Rooms You’re Not Using

If you’ve got a window AC in a guest room, home office or other space you don’t use regularly, turn it off when the room is unoccupied. Unlike central systems, window units don’t benefit from zoning — they cool exactly where they’re installed. Save your cooling power (and your dollars) for the rooms that need it.

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