Energy Efficient Products

Products that earn the ENERGY STAR are independently
certified to save energy, save money and protect the climate.

How To Choose the Right Sized Window AC

Choosing the right window air conditioning unit for your room will help keep you cool and save energy when the weather heats up. Here are three important factors to consider when buying a new AC:

  • Size
  • Features
  • Energy Savings

SIZE: How to properly size your room AC

Selecting the right sized unit is key to comfort and savings. Remember, bigger is not always better. —An over sized air conditioner will be less effective. Air conditioners remove both heat and humidity from the air, but if the unit is too large, it will cool the room, before it has a chance to remove the humidity. This will leave your room feeling damp and clammy. The most energy efficient air conditioner is one that is sized to the square footage of the space to be cooled.

To determine the size of the AC unit you’ll need, consider the size of the room you want to cool and what is typically happening in that room. Now, grab your tape measure, pencil and paper, and a smartphone or computer and let's figure out what size window ac will work best for you!

  1. Measure the length and the width of the room.
    • Tip: Always measure in feet. Convert inches to fractions of a foot: 9 in = .75 ft; 6 in = .5 ft; 3 in = .25 ft
      • For example: 12 ft, 6 inches = 12.5 ft
  2.  ​​​Determine the room's square footage.
    • Square and rectangular rooms: Multiply the length of the room by the width.
    • Triangular rooms: Multiply the length of the area by the width and divide by two.
    • Complex room shapes: Sub-divide into squares, rectangles and triangles. Then use the formulas above to determine the total square footage. 
      • For example: a rectangular room that is 14 ft, 9 inches long and 10 ft wide would be 147.5 sq ft (14.75 ft x 10 ft = 147.5 sq ft) 
  3. Look up the recommended cooling capacity for your room size using the table below.
    • Cooling capacity is measured in BTUs (British thermal units) per hour.
      • For example, 147.5 sq ft would need 5,000 BTUs;
  4. Make adjustments as necessary.
    • Once you have that number, you’ll want to make capacity adjustments depending on what is typically happening in that room.
      • 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 BTUs for each additional person.
      • If the unit is used in a kitchen, increase capacity by 4,000 BTUs.
      • Consider where you install the unit. If you are mounting an air conditioner near the corner of a room, look for a unit that can send the airflow in the right direction.
  5. Once you have a total, round down to the nearest thousand—that’s the number you should look for when choosing your unit.

FEATURES: What other features are available?

Once you have chosen the right sized unit, here are a couple of other things to think about.

  1. Look for the ENERGY STAR: Models that have earned EPA’s ENERGY STAR are independently certified to save energy, come with clearer instructions, and better materials to improve sealing and insulation around the unit. Certified units feature tight-fitting side panels that minimize costly and uncomfortable air leaks.
  2. Connected functionality: Some air conditioners offer great new features. ENERGY STAR models with connected functionality give you additional convenience, comfort, and savings with the ability to turn off the unit remotely, schedule temperature changes, and even receive feedback on the energy use of your unit.
  3. Environmentally friendly: Some ENERGY STAR room air conditioners come with an EPA-approved refrigerant called R-32, which has a much lower impact on the climate—two-thirds lower than the refrigerant used in other ACs.

What are room air conditioners with variable speed technology?

In a conventional room air conditioner, the compressor works either at maximum capacity when the room thermostat calls for cooling or off when the desired temperature has been achieved, typically alternating frequently between full on and off. Room air conditioners with efficient variable speed compressors can vary the speed of the internal compressor motor in order to continuously control the temperature. As a result, the capability for efficient variable output allows a room air conditioner to more quietly regulate the temperature and save a significant amount of energy during operation. Room air conditioner models with variable speed technology can now earn the ENERGY STAR.

SAVINGS: How can you save the most energy and money?

Use our Product Finder to help you choose an ENERGY STAR certified room air conditioner that suits your needs. Room ACs that have earned EPA’s ENERGY STAR use at least 10% less energy than standard models, and with improved insulation to prevent costly air leaks, you will pay less than $70 a year to run one, while helping protect the climate.

Author: Brittney Gordon