How to Choose, Install and Operate a Room Air Conditioner

Wednesday August 17, 2011
Posted at 08:15

Steps for choosing an energy efficient window air conditioning unit

Room air conditioners, also known as window air conditioners, can be a good choice when it comes to cooling one room at a time, especially if a central air conditioner isn’t needed. Here’s some helpful advice for choosing, installing and operating a room air conditioner.

The Truth About the Energy-Efficiency of Room Air Conditioners

In the past, room air conditioners have had a reputation for being inefficient when it comes to using energy. However, that reputation is no longer deserved according to the Association of Home Appliance Manufacturers, which reports that the average energy efficiency of room air conditioners increased 47 percent from 1972 to 1991. Now, although slightly less efficient than central air conditioners overall, room air conditioners do a more efficient — and cheaper — job of cooling individual rooms than their central air conditioner counterparts.

A room air conditioner’s energy efficiency is measured by its energy efficiency ratio (EER), which is the ratio of cooling capacity (measured in British thermal units [Btu] per hour) to the power input (measured in watts). The higher the EER, the more efficient the unit is.

Federal standards require room air conditioners to have an EER between 8.0 and 9.8 or greater, depending on the type and capacity of the unit. ENERGY STAR–certified units have even higher EER ratings. An older room air conditioner from the 1970s might have an EER of 5. If that unit were replaced with a new room air conditioner with an EER of 10, air conditioning energy costs would be cut in half.

Selecting the Right Room Air Conditioner

When shopping for a room air conditioner, the U.S. Department of Energy recommends new ENERGY STAR–certified room air conditioners that meet the following specifications:

Energy efficiency —New units should have EERs of 10 or above.

Size — A new room air conditioner needs to be able to meet your cooling capacity requirements. Cooling capacities are measured in Btu per hour, and generally range from 5,500 Btu per hour to 14,000 Btu per hour. A ton, a common rating term for cooling capacity, equals 12,000 Btu per hour. Each square foot of room space to be cooled needs about 20 Btu per hour of cooling capacity. So, to find the correct starting point for the size of your unit, multiply your square footage by 20. The result is the necessary Btu per hour rating of your unit. However, other factors to consider when selecting the size of a unit include room height, climate, shading and window size.

Electrical system requirements — Room air conditioners operate on either 115-volt or 230-volt circuits. The standard home uses a 115-volt circuit. Shoppers need to verify the power requirements of room air conditioners and consult with an electrician if necessary to determine if they need a dedicated circuit for large 115-volt unit or a special circuit for a 230-volt unit.

Special installation concerns — If a room air conditioner is to be installed at the far end of a narrow room, shoppers should look for a fan control known as “Power Thrust” or “Super Thrust” that does a better job of sending the cooled air across the room.

Other features to look for — Shoppers should also consider units that come with a slide-out filter for regular cleaning, a digital readout for the thermostat and a built-in timer.

Installing a Room Air Conditioner

There are a couple of things to consider when installing a room air conditioner. Make sure that the unit is level so that the interior drainage system and other parts of the unit operate as efficiently as possible. Additionally, try to install the unit in a shaded spot on a home’s north or east side so that the unit receives little direct sunlight. Direct sunlight can decrease the energy efficiency of room air conditioners by up to 10 percent. To help, consider planting trees or shrubs to provide shade, but make sure they don’t obstruct air flow around the unit.

Operating a Room Air Conditioner

To operate a room air conditioner efficiently, follow these simple guidelines:

- Set the unit’s thermostat as high as possible during the summer to save money on electric bills.
- Don’t set the thermostat to a colder temperature than is needed. Doing so won’t cool a room faster but can lead to excessive cooling and higher bills.
- Set the fan speed on high, except for on humid days. When humidity is high, a low fan speed will do a better job of removing the moisture form the air.
- Don’t place appliances that give off heat, like televisions and lamps, near room air conditioners. Heat from the appliances can trigger the thermostat into thinking the room is warmer than it is and cause the unit to run longer, which will result in higher energy bills.
- Use an interior fan to help more evenly spread the cooled air from the room air conditioner throughout the space without significantly increasing electricity use.

U.S. Department of Energy: Energy Savers website, “Room Air Conditioners.”

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