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Putting A/C in your home
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June 24, 1999: 6:28 a.m. ET
The right air conditioner will save you money, keep you cool
By Staff Writer Nicole Jacoby
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NEW YORK (CNNfn) - Perhaps you're enjoying the icebox office climate just a little too much. Or maybe you find yourself lingering in frosty movie theaters long after the credits have rolled.
Whatever your strategy, the motive is clear: anything to avoid the sweltering sauna you call home.
If you are desperate to stay cool, but haven't had the energy to hit the stores for an air conditioner, don't sweat it.
With the right information, shopping for an A/C unit doesn't have to be a flurried experience.
Size matters
The primary factor to consider when purchasing a new air conditioner is its cooling capacity, which is measured in British Thermal Units or BTUs per hour.
Air conditioners work by removing moisture from the air as the warm air is forced past cold coils. Cooling capacity is the amount of heat and moisture transferred from indoor air to outdoors, so the higher the BTU, the more powerful the unit.
A common mistake made by many consumers is buying an A/C that is simply too big in terms of BTUs.
"A lot of consumers think the largest unit is the best way to go, but that's not necessarily true," said Marian Stamos, vice president of major appliances at the Association of Home Appliance Manufacturers. "Bigger is not always better."
For one, an oversized air conditioner can leave rooms cold and clammy. A unit that is too large runs only for short bursts of time because the indoor coil never gets cold enough to remove moisture from the air. As a result, oversized units cool -- but do not dehumidify -- the air, reducing air quality and aggravating allergies.
In addition, oversized air conditioners tend to turn themselves on and off more frequently than properly-sized units, so they can run up your electricity bill. Air conditioners are most efficient when they run continuously for a long period of time.
Because oversized units emit cold air under most conditions, an A/C that is too large may keep you from noticing other problems, such as leaky ducts, constricted air flow, dirty filters, neglected coils or improper refrigerant charge.
Oversized units also tend to be louder.
Finding a good match
To determine what size air conditioner is right, you will have to measure the square footage of the room where it will be placed.
As a general rule of thumb, a room that is 250 square feet or smaller will need an A/C unit with about 5,000 BTUs, at a cost of about $250. Rooms larger than 550 square feet generally will require more than 11,000 BTUs, at roughly $500.
Ceiling height, the number of windows and the amount of direct exposure to sunlight could also affect the amount of BTUs needed.
If you're cooling three or fewer rooms, individual room air conditioners will likely be most cost-effective. However, if your space exceeds 1800 square feet and more than three units are necessary, a central air system may be better.
Installing a central air system can cost as much as $5,000, so you may want to consider air conditioners for just a few rooms, keeping doors to those spaces shut at all times to bolster efficiency.
Conserving energy
Energy efficiency is the key to lower electricity bills.
Once you have determined the BTUs needed, you will want to assess an air conditioner's Energy Efficiency Rating, which is computed by dividing BTU/hour by the watts of power used. The higher the EER, the more efficient the model.
"A 10 EER window-mounted room air conditioner will save about 20 percent in cooling costs over an 8 EER window-mounted air conditioner assuming your use, et cetera, is equivalent," said Jim Nanni, manager of the Home Testing Unit at Consumer Reports.
While energy-efficient units tend to be more expensive than less productive counterparts, the utility savings may make the extra expense worth your while.
Consumers need to consider "the difference between price and total cost," said Shorge Sato, spokesman for the Alliance to Save Energy. "The up-front price of most appliances is only a small fraction of total costs to you… By paying more up front, you can see substantial savings in the long run."
The Alliance to Save Energy estimates consumers can save anywhere from 10 to 40 percent in utility costs by using a high-efficiency air conditioner. The level of savings depends on what type of climate you live in, how big your home is and whether your A/C unit is properly sized.
Because the energy efficiency of air conditioners has improved greatly in the past two decades, current units can save an average of $26 per year in energy costs compared to air conditioners built in 1980.
Consequently, you may want to consider replacing an old air conditioner with a more current model to save electricity costs. However, proper maintenance should keep your unit efficient.
Keeping cool
To get the most out of your air conditioner, you will have to consider more than just BTUs and EERs.
"People tend to think that an air conditioner is a cure-all," said Sato. "But there are a number of different variables that go into room temperatures."
If you have windows that are heavily exposed to the sun, for instance, they may be admitting excessive heat into your home. Install blinds or opaque curtains on these windows during the day, or consider outdoor shading devices such as trellises or awnings. Leafy trees and vines can also provide shade, reducing indoor temperatures.
If your home has an attic, make sure it is well insulated. Attics and crawl spaces are exposed to extreme outdoor temperatures and can become as hot as 115 degrees. If that hot air leaks into the rest of your home, your air conditioner will have to work harder to cool the house down. Also close off unused rooms, so the air conditioner has less space to cool.
When setting up your air conditioner, make sure the air flowing in or out of the unit is not blocked by drapes or furniture. And take care that the area around the air conditioner is sealed and won't leak in hot outside air.
Finally, clean and replace the air conditioner's filter at least once a month. Dirty filters block the air flow, making A/Cs work harder. 
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