How to Select the Right Room Air Conditioner

Jun 10, 2014

There is no need to suffer through summer heat when inexpensive, energy-efficient air conditioners are widely available. Since June 1, 2014, all room air conditioners have been required to meet a new standard that set maximum power use at 10-15% less than older models following the 2000 guidelines. And, when 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 an EER of at least 11 and 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 15% 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 over-sized 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- 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

Our Picks


Small rooms (up to 150 square feet)

The GE AEL06LS ($179.00 on, rated at 6,050 BTU, gets high marks for its cooling capabilities. The unit, which has an EER of 11.2, has two cooling and two fan speeds, a 24-hour programmable timer and a two-way adjustable vent to direct air flow.


Large rooms (up to 550 square feet)

The highly-rated LG LW8014ER ($239.00 on Amazon) delivers 8,000 BTU, enough to cool a room up to 340 square feet, with an EER of 11.3. The unit has three cooling and three fan speeds, a 24-hour programmable timer and a four-way directional vent to stream air where you want it. For rooms up to 550 square feet, we like the LG LW1214ER ($349.00 on step-up model, which has all the same features, but delivers 12,000 BTU with an EER of 11.3.

Installing and Operating Your Room Air Conditioner

A little planning before installing your air conditioner will save you money and energy. 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 (BTU) 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 BTU for each additional person.
    • If the unit is used in a kitchen, increase capacity by 4,000 BTU.
    • 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
    (BTU per Hour)
    100 to 1505,000
    150 to 2506,000
    250 to 3007,000
    300 to 3508,000
    350 to 4009,000
    400 to 45010,000
    450 to 55012,000
    550 to 70014,000
    700 to 1,00018,000
    1,000 to 1,20021,000

    Information for this article comes courtesy of the U.S. Department of Energy. This article was written by Josh Kirschner and originally appeared on Techlicious.

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