What the best air conditioner has

  • Eco-friendly cooling: Look for an air conditioner that uses R-410A as a refrigerant. Not only is it more environmentally friendly than R-22, but it's cheaper and easier to find when you need to recharge your unit.
  • Energy efficiency: Every window air conditioner has an Energy Efficiency Rating, or EER. This is a measure of how much electricity it uses -- the higher the EER, the better. The best air conditioners have at least a 10.0 EER and an Energy Star rating.
  • A programmable timer: A built-in timer gives you the power to turn your window air conditioner on and off even when you aren't around. This cools your room when you need it while saving you money on your electric bill. A 24-hour timer is best, which reviewers say is handy to cool off a room before they come home or to tag team with a central air conditioner at night.
  • User-friendly controls: For setting the temperature, digital controls are more precise than a knob, which typically has only a generic range of warmer to colder. For extra convenience, a remote control lets you adjust the temperature and fan speed from across the room. The best remotes also include buttons to set the timer and toggle through the different air conditioner modes.
  • Dehumidifier: Air conditioners pull moisture out of the air as they cool, lowering the humidity in your room to make it more comfortable. Top air conditioners have a separate dehumidify mode, which is ideal for humid days without high temperatures, like in the spring and fall.
  • Adjustable airflow: The best window air conditioners have louvers that are adjustable and effective, cooling specific zones in your room or diverting the air from blowing directly on you. Experts compare these to the vents in a car: The best designed louvers aim the air in a general direction, but few are very precise.
  • An air filter: Window air conditioners with built-in filters help freshen the indoor air. Units with an electronic ionizer go one step further by filtering out odors and smaller impurities. For user-friendly maintenance, select an air conditioner with a filter that is washable and easy to remove. An indicator light on the front is extra-convenient, reminding you that it's time to clean the filter.
  • Warranty: A one-year warranty is standard with many air conditioners, but the best brands also cover the sealed system and compressor for five years.

Know before you go

How much cooling power do you need? The power of an air conditioner is measured in Btu, short for British thermal units. The higher the Btu, the larger the area it can cool. But bigger is not automatically better. It's important to match the size of your air conditioner to the needs of your room: It must be powerful enough to keep your space cool, but not so large that it shuts off too soon (which leaves too much moisture in the air).

  • Up to 150 square feet: A small air conditioner is best, with 6,000 Btu or less.
  • 200 to 300 square feet: Select a medium air conditioner in between 7,000 and 8,000 Btu.
  • More than 300 square feet: With a minimum of about 9,000 Btu, a large air conditioner is necessary to cool bedrooms and living spaces greater than 300 square feet (which is the equivalent of 15 feet by 20 feet).
  • Kitchens: So much heat is produced in a kitchen, that this area needs serious cooling power. Start by estimating the size of the room, then add 4,000 Btu to calculate the size of the unit you need.
  • Sunrooms and areas with large windows: An area bathed in excessive sunlight also warms up more than usual. Figure out the square footage of the room, then add 10 percent more Btu.

How large is your window? Measure your window opening before you start shopping, as some extra-wide units won't fit in smaller windows. Most window air conditioners are designed for windows that slide up and down. Look for a casement window air conditioner if your windows slide to the side or are hinged.

If a nearby outlet is required. Air conditioners draw a lot of power, so you need an outlet that can supply the right amount of power and is close enough for the window air conditioner to plug directly into. If the nearest outlet isn't right below the window, measure the distance from the unit to the outlet and look for a unit with a long enough cord. Never use an extension cord with an air conditioner.

Keeping your air conditioner in good shape. Maintenance is uncomplicated for most window-mount air conditioners, but a little regular cleaning is important to keep mold under control (especially in moist climates). Most built-in filters require washing once a month; replace disposable filters at least once a season or as the manual recommends. Clean the drip tray thoroughly at the end of summer to remove mildew, dust and pollen.

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