In this report, we cover room-sized air conditioners designed to be installed in a window. If that type of installation is impossible or impractical for your needs, see our report on portable air conditioners. Those units don't work as well as window ACs and are a lot more expensive, but a portable air conditioner can be a viable alternative if you can't install a window model.
When selecting your air conditioner, it's important to match the size of the unit to the size of the space you wish to cool. Smaller ACs tend to be less expensive than their larger counterparts, but it's easy to underestimate your cooling needs. On the other hand, don't fall into the trap of buying more air conditioner than your space really requires. "Too much capacity and the unit will cycle on and off too often, wasting energy," cautions the American Council for an Energy-Efficient Economy (ACEEE); ConsumerReports.org adds that this can leave the room uncomfortably damp. See the sizing chart on our What to Look For page to help you determine what size unit you need.
Reviewers say most modern window air conditioners do a pretty good job of cooling a room, as long as you buy the right size unit for the space you need to cool. Noise is the big complaint in consumer reviews at Amazon.com, Sears.com, AJMadison.com and elsewhere, especially if you need an AC for a bedroom. Among professional reviewers, ConsumerReports.org is by far the leader in testing window air conditioners, and even has a dedicated lab to do just that. EnergyStar.gov publishes a frequently updated list of Energy Star-rated air conditioners, but it's based on analyzing efficiency data. Only ConsumerReports.org tests actual performance.
Still, the Energy Star rating is important: With energy prices rising across the country, an extra point or two in an appliance's energy efficiency ratio (EER) can make a difference on your monthly power bill. And, as ConsumerReports.org points out, AC units with higher EERs are usually no more expensive than non-Energy Star-rated room air conditioners. All of the Best Reviewed models in this report are Energy Star-rated. They also all restart automatically after a power outage -- an especially important feature if you have pets that could suffer in a hot room.