Consider room size. This is a case where the right size is important. A unit that is too small won't do a good job of cooling, but a unit that is too large won't do a good job of dehumidifying.

Measure the size of the room you're cooling and consult a sizing chart to determine the number of Btu needed to cool that area. The U.S. Environmental Protection Agency, for example, has a guide to help you decide what kind of power you need. Generally, a 150-square-foot room requires a Btu/hour of 5,000 and a 300- to 350-square-foot room needs about 8,000 Btu. Make adjustments for amount of sun vs. shade, number of people in the room and whether or not it is the kitchen.

Consider installation issues. Installation may be getting easier, but it's still a pain. A slide-in chassis is easier to use than a heft-and-balance system, and through-the-wall units require -- you guessed it! -- cutting a hole in your wall.

Take into account outside conditions. Direct sunlight, just like bountiful shade, has a direct influence on the temperature of your home and how well your air conditioner works. Humidity and how many people occupy the room are factors as well.

Calculate the cost of using it. Unless you only occasionally use your air conditioner, most of the cost associated with an air conditioner is the day-to-day operating cost (electricity) rather than the initial purchase price. Energy-efficient models may cost more initially, but you'll more than make up for the higher purchase price in terms of lower electric bills.

Room air conditioners have an Energy Efficiency Rating (EER) -- Btu/hour divided by number of watts required -- of 8 to 11.5; the higher the rating, the more efficient the model will be. Also, look for models that have earned the Energy Star rating from the U.S. Environmental Protection Agency. Energy Star room air conditioners must exceed minimum federal standards for energy consumption by at least 15 percent.

Watch for special needs. The best air conditioner is one that just works when you plug it in. But that's not always the way it works out: Make sure you check the voltage and mounting needs of the model you want.

Check ease of adjustment. Most models have louvers to direct cool air, but how easy and flexible are they? Also, see how hard it'll be to replace the filter: You should do it every six weeks to cut down on airborne nasties.

Disclaimer: The staff of Appliance411.com does not necessarily agree with the opinions expressed by Productopia.com. The information and links are presented for reference only.