What the best air conditioner has
- Energy efficiency. Every window air conditioner has an Energy Efficiency Rating, or EER, and a Combined EER, or CEER, which measures both how much energy the unit uses while running, as well as the standby energy it uses when off. Since June 2014, the CEER rating is what's considered by the Department of Energy for efficiency standards, including Energy Star qualification, which varies from 9.9 to 12.1, depending on the cooling capacity and type of unit.
- 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. A remote control adds convenience. The best ones include a digital readout, let you adjust the temperature from across the room, and have buttons to set the timer and toggle through the different air conditioning modes. Even more helpful is a temperature-sensing remote, which measures the temperature where you are sitting or sleeping, instead of at the unit where temps tend to be cooler.
- Good dehumidification. Air conditioners pull moisture out of the air as they cool, lowering the humidity in your room to make it more comfortable. Some air conditioners have a separate dehumidify mode, which is ideal for humid days without high temperatures, like in the spring and fall, or during summer rains.
- 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. 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, though experts aren't sure they actually perform any better than standard filters. 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.
- A good warranty. A one-year warranty is standard with many air conditioners, but some 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). The Energy Star website provides the appropriate BTU capacity for different sized rooms, how to accurately calculate room size, and how to compensate for factors such as shade, sun and room usage.
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 window mounting is not possible or is undesirable, consider an air conditioner that mounts through the wall. However, in-wall room air conditioners are often costlier than equivalent window air conditioners and have other drawbacks, as outlined in the introduction of this report.
What about the electricity? Air conditioners draw a lot of power, so you need a nearby outlet that can supply it satisfactorily. All of the models mentioned in this report work on 115 volts, the standard voltage for residential electrical service in the U.S. However, the circuit also needs to be able to handle the air conditioner's current needs (measured in amps). If the wiring isn't rated to handle that, or if the circuit is shared with other appliances, you might need the help of a licensed electrician to sort things out. It's also best to pick a window that's in reach of the air conditioner's cord. Using an extension cord isn't the greatest idea, but if necessary, be sure to use a major appliance extension cord that's rated to handle the current draw of your air conditioner.
Keeping your air conditioner in good shape. Maintenance is uncomplicated for most in-wall and 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.