Home Series Booklets

How to buy a room air conditioner

Size and efficiency | Free Copy | Art files

Room air conditioners-sometimes called window units-mount in a hole cut into an exterior wall or in a window frame. (Portable units that roll from room to room and vent through a window also are available.) Room air-conditioning units are designed to cool one room at a time, and you would need multiple units to cool an entire house. However, room air conditioners are a good choice if you only need to cool one or two rooms, live in an apartment or own a very small, well-insulated home. One or more energy-efficient room units can be less costly to run than an older, full-sized central air-conditioning system; on the other hand, a couple of older room units can be more expensive to operate than a new central unit.

Energy-efficient room air conditioners are moderately inexpensive and fairly easy to install in a wall using basic carpentry skills-although some models weigh around 100 pounds, so installation could be a two-person job. For peak operating efficiency, locate room air conditioners on the north side of your home or in shaded areas-and, if possible, in the middle of each room for better air distribution. The opening around the unit, whether it's mounted in a wall or window, must be sealed to prevent air leaks. And if you don't remove the unit every fall for winter storage, cover it with a fitted, insulated blanket made specifically for that purpose to keep cold air from infiltrating your home.

Consider size and efficiency
A room air conditioner that's sized correctly will handle both the heat and humidity in a room. Some people buy an oversized unit, assuming that it will do a better job of cooling. But remember that an air conditioner must remove heat and humidity from the air, and it's designed to do both during a normal cycle. A unit that's too large may cool a room quickly, but the resulting short cycle won't allow it to reduce the humidity to an acceptable level.

The cooling capacity (size) of a room air conditioner is measured in Btu/hour (British thermal units per hour) and is dependent on the square footage of the room you want to cool. After figuring the square footage of the room, use this chart from ENERGY STAR® to estimate what size air conditioner best fits your needs.

If the room is on the sunny side of your house, increase the air conditioner's capacity by 10 percent; if the room is shaded, subtract 10 percent. For a kitchen-mounted unit, boost the capacity by 4,000 Btu/hour. And if more than two people usually occupy the room, add 600 Btu/hour for every additional person.

At the store, look for the ENERGY STAR designation on the yellow EnergyGuide label for each air conditioner. Also check each unit's EER-Energy Efficiency Ratio-the unit's cooling output (Btu/hour) divided by its power consumption. The minimum federal standard is an EER of 9.7, while ENERGY STAR qualified units must have an EER of 10.7 or higher. Buy the most efficient room air conditioner your budget allows; you'll more than make up the higher initial cost of the unit through future energy savings.

Sidebar

The material in this article was adapted from Home Heating and Cooling, a book published by the Iowa Energy Center. Besides offering more details on the topics discussed here, this publication also covers energy-saving home improvement projects that may be eligible for rebates from local utility companies; low-income assistance and grant programs; special financing opportunities from banks, credit unions and other lending institutions; state incentives; and federal income tax credits.

To get a free copy of this book:

• Call your utility company to see if you can stop by the office and pick up a copy;
• Download a PDF copy at the Iowa Energy Center Web site: http://www.energy.iastate.edu/;
• Request a copy by e-mailing the Iowa Energy Center at iec@energy.iastate.edu; or
• Call the Iowa Energy Center at 515-294-8819 to ask for a copy to be sent to you by mail.

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Contct: Amy Myers, Iowa Energy Center, (515) 294-4391, myers@energy.iastate.edu