The most efficient air conditioners on the market are up to 70% more efficient than the typical room air conditioners found in homes today. 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 required cooling capacity depends on the size of the room being cooled. The higher the EER rating, the more efficient the air conditioner. Look for units with an EER of 10.0 or above. Check the EnergyGuide label for the unit, and also look for room air conditioners with the ENERGY STAR® label.

Proper sizing is very important for efficient air conditioning. A bigger unit is not necessarily better because a unit that is too large will not cool an area uniformly. A small unit running for an extended period operates more efficiently and is more effective at dehumidifying than a large unit that cycles on and off too frequently. Based on size alone, an air conditioner generally needs 20 Btu for each square foot of living space. Other important factors to consider when selecting an air conditioner are room height, local climate, shading, window size, etc.

Verify that your home's electrical system can meet the unit's power requirements. Room units operate on 230-volt circuits.

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, then look for a fan control known as "Power Thrust" or "Super Thrust" that sends the cooled air farther 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

Read also "Routine Air-condition Maintenance"