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Room Air Conditioning

Room Air Conditioning Units are used to cool single rooms or small zones within a house and typically have a lower efficiency than Central AC systems.


A room air conditioner transfers heat — from the inside of a building, where it is not wanted, to the outside. The compressor sends cooled refrigerant through the coils. The refrigerant draws heat from the air as it is forced over the coils. A fan blows outside air over the hot coil, transferring heat from the refrigerant to the outdoor air. Because the heat is removed from the indoor air, the indoor area is cooled.

By using advanced heat transfer technologies, ENERGY STAR qualified room air conditioners transfer more heat from the air into the coils than conventional models transfer, saving the energy required to compress the refrigerant.

If you choose to install a room air conditioner for zone cooling, find a unit with an EER of 10 or more. Properly size the unit to the space because oversized units will cycle on and off frequently, affecting their ability to reduce humidity levels. Direct sunshine on the outdoor components can reduce efficiency by as much as 10%, so ideally window units should be installed in a shady area on the north or east side of the house. Room air conditioners may be an effective solution if air conditioning is rarely called for. However, if air conditioning is desired on a daily basis for most of the cooling season, consider investing in a ductless heat pump.

Room Air Conditioning Efficiency Ratings

A room air conditioner’s efficiency is in EER. The higher the EER rating, the more efficient the air conditioner. National appliance standards require room air conditioners to have an energy efficiency ratio (EER) ranging from 8.0–9.8 or greater, depending on the type and capacity, and ENERGY STAR® qualified room air conditioners have even higher EER ratings.

When buying a new room 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.

Sizing and Selecting 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. A common rating term for air conditioning size is the “ton,” which is 12,000 Btu per hour.

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. The oversized unit will also cool the room to its thermostat set point and shut down prior to properly dehumidifying the room, leaving the area feeling damp or “clammy.” 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, and window size.

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 include:

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