How to Choose an Air Conditioner Buying a room air conditioner: How big? One Size Doesn't Fit All Matching the air conditioner to the room you want to cool is your first consideration. If it's too small, it simply won't cool the space. If it's too large, it will cool the space so quickly that the thermostat will shut the unit down before it can lower the humidity level in the space. The result is a cool room that feels damp and clammy. Room air conditioners are "sized" according to their cooling capacity, expressed in Btu per hour. You'll find the rating on packaging or in product literature; it typically ranges from 5,000 to 25,000 Btu. Units below 12,000 Btu start at $250 to $300. Those in the 12,000- to 15,000-Btu range cost from $450 to $600, while large units go up to $1,200. Air conditioners rated at 15,000 Btu should be enough to cool most rooms up to about 875 sq. ft. How do you get more precise than that? There are several different formulas. Most of the ones you'll see in stores simply compare the square footage of the room to Btu capacity.

The Association of Home Appliance Manufacturers (AHAM), a Chicago-based industry trade group, offers a more complete formula that includes window area, sun exposure, insulation levels, how the room is used and other variables. How Much Do You Need? For a calculation of the cooling capacity your space requires, use our Air Conditioning Calculator. You can get a free copy of the formula from the AHAM fax-on-demand service or through the organization's site on the Web. Although the form looks daunting, it takes only a few minutes with a calculator and tape measure to figure out the square footage of the room and measure a few other variables. Whichever way you determine the size you need, remember that for the 115V circuits typical of bedrooms and living rooms, you'll have to stay below 15,000 Btu; units above 15,000 Btu usually require a 230V circuit. And if you want to cool a large, open L- or T-shaped space, you're better off with two smaller units rather than one large one.

"The goal is to keep the cold air from pooling on the floor," explains Hank Rutkowski, director of technical affairs for the Washington, D.C.-based Air Conditioning Contractors of America. "Two units prevent cold spots in front of the air conditioner and warm spots around the corner."replacement rv ac unit Where to Find Itcentral air conditioning units cost replace unit Amana Home AppliancesAmana, IA 52204800-843-03042 ton ac unit size The Association of Home Appliance Manufacturers 20 N.Wacker Dr.Chicago, IL 60606312-984-5800 Box 4808Syracuse, NY 13221 Emerson415 Walbash Ave.Effingham, IL 62401800-332-6658 Fedders North America415 Walbash Ave.Effingham, IL 62401800-332-6658 Friedrich Air Conditioning Co.Box 1540San Antonio, TX 78295-1540800-541-6645

Whirlpool Corp.Consumer Assistance CenterBenton Harbor, MI 49022800-253-1301Older central and window air units cost more to run than newer ones. Air conditioning makes the hottest summer days more enjoyable, but rising energy costs and the growing awareness of energy conservation and resource depletion demands you cool your home as cheaply and energy efficiently as possible. Deciding which cooling method will save you the most -- three window air conditioners or a central air unit -- depends on a few factors. Cooling your home with the proper system saves you money and electricity, and keeps you completely comfortable no matter the temperature outside. Comparing Energy Usage Considering that the average home uses more electricity for cooling than for any other appliance or accessory, if you want to save money on your utility bill, carefully consider your cooling choices. A central air unit uses more energy to cool your home. As Mr. Electricity states, a window unit uses anywhere from 500 to 1440 watts to run, while a 2.5 ton central unit (about the size for a typical 1,500- to 2,000-square-foot home) uses about 3,500 watts.

It's not simply about the size of area cooled, but the fact that central air involves the furnace, too. The air does not flow to the rest of the house without the furnace blower -- so more running parts equal a larger power draw. Cost of Unit Installation It's simple to see that a central unit uses more power than a window unit, but there's more to your cost than just the energy draw. Once you factor in the purchase price and cost of installation, your cost per use may rise significantly. Dividing the total price and installation labor cost by the months you use it dramatically illustrates the true cost of just having the air conditioner, without figuring in the utility bill. Window units sell for a lot less than central units, and the installation typically is do-it-yourself. It's Not All About the Unit Another factor when determining which cooling unit is best for your circumstances is the condition of your existing HVAC system. No matter how efficient your central air unit, if the ducts the cool air travels through are full of holes, or poorly insulated and exposed to temperature extremes, the efficiency of the whole system goes down -- and the cost goes up.

If you choose to run a central air unit, insulating your ducts, and inspecting and maintaining the whole system is important, although it adds to the cost. Compared with window units, which blow directly into the room and need little but occasional cleaning unless they go out, a central unit again costs more. Verdict Although it costs more to purchase and install a central unit -- and responsible owners also spend more on annual service calls for maintenance and inspection -- if you plan to cool three or more rooms, the most cost-effective and energy-efficient choice is the central unit. A central unit has greater resale value, so you recoup more of your investment if you sell your home. The weightiest factor, however, is that three window units typically use more energy than a single central unit. Also consider that three rooms likely is a large portion of the home, and every time you travel between cooling zones with a window unit, you're leaking cool air, making your unit work harder.