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Choosing the Right Portable Air Conditioner (AC) Size

How to Choose the Right Size Portable Air Conditioner (AC)

When choosing a portable air conditioner most people falsely assume that "bigger is better". Unfortunately that line of reasoning may cause real trouble. A portable ac unit that is too large may actually waste energy and do a poorer job of controling both the right temperature and humidity.

When discussing the proper size air conditioner the primary concern is the number of BTUs (or British Thermal Units) it is rated for. The higher the BTU rating the more cooling capacity the air conditioner has. Portable ac units are typically rated between 5,000 and 12,000 but higher rated portable units are available. In order to get the best value and fit you will need to get a measurement of the square feet for the particular room you are hoping to cool. If you plan on using a portable air conditioner in multiple rooms use the square footage number from the largest of the rooms.

Below is a chart with which you can determine the proper number of BTUs your air conditioner needs to be. The information came from EnergyStar a government-backed program intended to help businesses and individuals protect the enviornment through superior energy efficiency.

To figure out which size unit is best for your cooling needs:

1. Determine the square footage of the area to be cooled using the following formulas:

  • For square and rectangular rooms, multiply the length of the area by its width
  • For a triangular area, multiply the length of the area by the width and divide by 2

Most rooms can be further divided into these basic shapes to determine the square footage.

If the shape of your room is other than square or rectangular, ask your sales associate to help you determine the square footage.

2. Using the square footage and the chart below, determine the correct cooling capacity. Cooling capacity is measured in British thermal units (BTUs) per hour.

Area To Be Cooled (square feet) Capacity Needed (BTUs per hour)
100 to 150 5,000
150 to 250 6,000
250 to 300 7,000
300 to 350 8,000
350 to 400 9,000
400 to 450 10,000
450 to 550 12,000
550 to 700 14,000
700 to 1,000 18,000
1,000 to 1,200 21,000
1,200 to 1,400 23,000
1,400 to 1,500 24,000
1,500 to 2,000 30,000
2,000 to 2,500 34,000

3. Make any adjustments for the following circumstances:

  • 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.


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