How to Buy an Air Conditioner

Air conditioner sizing

Sources differ on how large of a window AC unit you should buy for a room of a given size, and experts say factors such as doors, windows and sun exposure, and high ceilings will all increase the output capacity (measured in British thermal units, or BTU) you'll need. ConsumerReports.org's sizing estimates are lower than those of the federal government's Energy Star size chart. We've combined the two to give you a general air conditioner sizing guide. Calculate square footage by multiplying the length by the width of your room.

Climate can also make a major difference in air conditioner efficiency, so keep in mind the standard calculations used in these charts are based on summer temperatures in the high 80s and low 90s. If you live in a milder climate, you can save money and energy by buying a less powerful air conditioner. On the other hand, if high temperatures in your area frequently exceed 100 degrees, you may need an air conditioner with about 50 percent higher output. This is especially true in areas with high humidity.

For room air conditioners with a capacity of less than 8,000 BTU, the EER must be at least 9.7 (the higher the number, the better). For a model to receive an Energy Star rating, it must reach 10.7 EER. You can estimate energy savings by calculating a 10 percent savings for each point difference of EER. For example, a model rated at 10.7 EER is 10 percent more efficient than a 9.7 EER model. By estimating the number of years you expect to use the unit, you can gauge whether a higher initial cost will eventually pay off. All new appliances are required to carry a bright yellow EnergyGuide decal that lists the unit's energy consumption in kilowatts and estimates annual cost of operation.

Air conditioner shopping tips

Here are some other considerations to bear in mind when shopping for a room air conditioner:

• Get the right size. Air conditioning is half cooling, half moisture removal. A unit that's too small for your room won't cool enough, while one that's too large won't remove humidity effectively. ConsumerReports.org's handy article "How Powerful an Air Conditioner Do You Need?" can help you determine what size air conditioner is right for your room. A less detailed guide, "Window Air Conditioner Estimator," is available from WarmAir.net.

• Consider ease of installation. Even the smallest air conditioners are heavy, and the largest can weigh more than 100 pounds. You'll probably need assistance to install a heavier AC; even with a lighter unit, an extra pair of hands is a good idea. Many units also require special installation. A slide-in chassis makes installation easier because you install the lighter portion first, but this means it can also take more time.

• Check for special requirements. Some extra-large window air conditioners require a 220-volt plug, and some have louvers that blow air in multiple directions -- a feature worth considering, depending on where you plan to install the AC. The filters in certain units may require additional space on one side, so be sure to check out how easy it is to install and remove the filter once the unit's in place. The models in the ConsumerSearch Best Reviewed section all require a three-prong outlet. Experts recommend that you run an air conditioner on its own circuit to avoid electrical overload.

• Look for convenience features. Thermostats, digital controls, remote controls and built-in timers are becoming more common, even on low-priced models.

• Know what level of noise you can live with. You may be willing to save some money on a noisier unit if you're not cooling a bedroom, but look for models known for quiet operation if you're a light sleeper.

• Get the highest-efficiency unit you can afford. In general, you'll pay a bit more for a high-efficiency air conditioner, but you'll make up the difference in your electricity bill over the unit's lifetime. Price differences have diminished between high- and low-efficiency air conditioners, and sometimes more efficient models are no more expensive than others.

Some features may not be worth paying extra for. Sleep mode increases the thermostat's temperature (usually to 78 degrees) to save energy costs when you're asleep and may not notice a warmer room. But according to the National Sleep Foundation, sleep researchers have found that temperatures of more than 75 degrees often disrupt sleep. Experts typically recommend keeping your bedroom at about 68 degrees for the most restful sleep, so if you tend to wake easily at night, avoid using the sleep mode setting on your air conditioner.

Energy-saver mode is another feature that isn't always as useful as it sounds. It works by turning off the air conditioner's fan when the room's temperature reaches the desired level and the compressor shuts off. However, leaving the fan on will make the room feel cooler and may allow you to turn the thermostat up a degree or two, saving more energy overall. In addition, the changing noise level might awaken you.