A room air conditioner is a small, self-contained, air-conditioning unit designed to cool one room of a home. While most room air conditioners are placed in windows, some models go through an exterior wall. A room air conditioner tends to be less efficient than a central air conditioning system. 
 

Reducing the energy consumption of your air conditioner

There are two primary ways to control the energy usage of your room air conditioner:

• Reduce unnecessary usage.
• Purchase an energy-efficient air conditioner.

Steps you can take to reduce unnecessary usage include the following:

• Consider setting your air conditioner at a warmer temperature than you normally would (for example, “low cool” rather than “high cool”).
• Turn the unit off when no one is in the room. If you need to leave the system on, be sure to set it at a warmer temperature when you leave the room.
• To keep your room air conditioner running efficiently, check your filter once a month. Clean and replace it as needed.
• If possible, position the exterior portion of your room air conditioner in the shade or on the north side of your home. A cool air conditioner can save up to 10% on your air conditioning usage.

When you’re ready to shop for a replacement room air conditioner, keep the following tips in mind:

• To keep energy costs down, purchase the right size unit. An air conditioner that is too large does not necessarily provide more cooling because it will need to cycle on and off more often, leading to a less comfortable environment. It also will cost more and consume more energy than a properly-sized unit. Your sales professional can help you determine the appropriate size unit for your needs.
• As room air conditioners are less efficient than centralized air conditioners, consider upgrading to a centralized system if you use room air conditioners in more than half the rooms in your home.
• Buy the most energy-efficient model your budget will allow. Look for the ENERGY STAR^® label and read the yellow EnergyGuide label to fully compute the cost of ownership over the lifetime of the unit. New ENERGY STAR^®-qualified models are almost twice as efficient as standard models purchased in 1970.
• Consider upgrading insulation and windows, as well as installing weather stripping, prior to purchasing an air conditioning system. You can save money by purchasing a smaller system—and by keeping the cool air indoors, where you want it.
• For best results, make sure your room air conditioner is properly installed. Openings around a poorly-fitting room air conditioner can let cold air out of your home.

Energy efficiency in room air conditioners

A high-efficiency room air conditioner usually has one or more of the following:

• High-efficiency compressor: Uses less energy to move the refrigerant.
• Variable-speed fans: Slow the fan speed when less cooling is needed.
• High-efficiency motors: Use less energy to drive air through the fan.
• Improved heat exchangers: More efficiently extract heat from the air.

Measuring energy efficiency in air conditioners

Air conditioners are rated in either British Thermal Units (BTUs) or tons (one ton = 12,000 BTUs). This is a measure of how much heat they can remove per hour.  An air conditioner efficiency rating will measure the amount of BTUs removed per watt of electricity used.

The primary rating system used for room air conditioners is Energy Efficiency Rating (EER). It is important to keep EER in mind when purchasing a new air conditioner. Room air conditioners have a minimum standard EER of 8.0 to 9.8. ENERGY STAR, a joint initiative of the U.S. Department of Energy and U.S. Environmental Protection Agency, is a handy labeling tool that identifies the top energy-efficient appliances. ENERGY STAR air conditioners have an EER rating up to 11.7. The higher the EER rating, the more efficient the unit.