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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-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.

Our Picks
Small rooms (up to 150 square feet)

The GE AEL06LS ($179.00 on, rated at 6,050BTU, 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.
LG LW8014ERLarge rooms (up to 550 square feet)

The highly-rated LG LW8014ER ($239.00 on Amazon) delivers 8,000 BTUs, 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 4-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 12,000BTUs with an EER of 11.3.

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