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Select the Right Room Air Conditioner

by on May 25, 2009
in Health and Home, Home Improvement, Tips & How-Tos :: 0 comments

Information for this article comes courtesy of the U.S. Department of Energy

Friedrich CP06E10

There is no need to suffer through summer heat when inexpensive, energy-efficient air conditioners are widely available. And, if used to provide cooling only where they're needed, room air conditioners are less expensive to operate than central units.  This guide will help you find the model that is right for you.

Energy Efficiency of Room Air Conditioners

A room air conditioner's efficiency is measured by the energy efficiency ratio (EER). The EER is the ratio of the cooling capacity (in British thermal units [Btu] per hour) to the power input (in watts). The higher the EER rating, the more efficient the air conditioner. Each increase of 1.0 on the EER scale represents a 10% increase in energy efficiency.

When buying a new room air conditioner, information about the EER can be found on the EnergyGuide label for the unit. Look for units with an EER of 10.0 or above and also look for room air conditioners with the ENERGY STAR® label. Earning the ENERGY STAR means a product meets strict energy efficiency guidelines set by the U.S. Environmental Protection Agency and the U.S. Department of Energy.

  • ENERGY STAR qualified room air conditioners use at least 10% less energy than conventional models.
  • ENERGY STAR qualified room air conditioners often include timers for better temperature control, allowing you to use the minimum amount of energy you need to cool your room.

Properly Sizing a Room Air Conditioner

The required cooling capacity for a room air conditioner depends on the size of the room being cooled. Room air conditioners generally have cooling capacities that range from 5,500 Btu per hour to 14,000 Btu per hour.

Many people buy an air conditioner that is too large, thinking it will provide better cooling. However, an oversized air conditioner is actually less effective — and wastes energy at the same time. Air conditioners remove both heat and humidity from the air. If the unit is too large, it will cool the room quickly, but only remove some of the humidity. This leaves the room with a damp, clammy feeling. A properly sized unit will remove humidity effectively as it cools.To figure out which size unit is best for your cooling needs, see the Air Conditioner Cooling Needs Calculator below.

Other Factors to Consider when Buying

Verify that your home's electrical system can meet the unit's power requirements. Room units operate on 115-volt or 230-volt circuits. The standard household receptacle is a connection for a 115-volt branch circuit. Large room units rated at 115 volts may require a dedicated circuit and room units rated at 230 volts may require a special circuit. If you are mounting your air conditioner near the corner of a room, look for a unit that can direct its airflow in the desired direction for your room layout. If you need to mount the air conditioner at the narrow end of a long room, look for models that have a “turbo” fan mode that can drive air further into the room. Other features to look for:

  • A filter that slides out easily for regular cleaning
  • Logically arranged controls
  • A digital readout for the thermostat setting, and
  • A built-in timer.

Installing and Operating Your Room Air Conditioner

A little planning before installing your air conditioner will save you energy and money. The unit should be level when installed, so that the inside drainage system and other mechanisms operate efficiently. If possible, install the unit in a shaded spot on your home's north or east side. Direct sunshine on the unit's outdoor heat exchanger decreases efficiency by as much as 10%. You can plant trees and shrubs to shade the air conditioner, but do not block the airflow.

Don't place lamps or televisions near your air-conditioner's thermostat. The thermostat senses heat from these appliances, which can cause the air conditioner to run longer than necessary.

Set your air conditioner's thermostat as high as is comfortably possible in the summer. The less difference between the indoor and outdoor temperatures, the lower your overall cooling bill will be. Don't set your thermostat at a colder setting than normal when you turn on your air conditioner; it will not cool your home any faster and could result in excessive cooling and unnecessary expense.

Set the fan speed on high, except on very humid days. When humidity is high, set the fan speed on low for more comfort. The low speed on humid days will cool your home better and will remove more moisture from the air because of slower air movement through the cooling equipment.

Consider using an interior fan in conjunction with your window air conditioner to spread the cooled air more effectively through your home without greatly increasing electricity use.

Air Conditioner Cooling Needs Calculator

To determine the correct size Air Conditioner for your room, follow these easy steps:

  1. Determine the square footage of the area to be cooled.
  2. Using the square footage and the chart below, determine the correct cooling capacity. Cooling capacity is measured in British thermal units (BTUs) per hour.
  3. Make any adjustments for the following circumstances:
  • If the room is heavily shaded, reduce capacity by 10 percent.
  • If the room is very sunny, increase capacity by 10 percent.
  • If more than two people regularly occupy the room, add 600 BTUs for each additional person.
  • If the unit is used in a kitchen, increase capacity by 4,000 BTUs.
  • For the purpose of this chart, rooms that are connected by permanently open entryways wider than five feet ought to be considered as one room and their square footage should be combined.
Area to be Cooled
(Square Feet)
Capacity Needed
(BTUs per Hour)
100 to 150 5,000
150 to 250 6,000
250 to 300 7,000
300 to 350 8,000
350 to 400 9,000
400 to 450 10,000
450 to 550 12,000
550 to 700 14,000
700 to 1000 18,000
1000 to 1200 21,000

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