Ductless Mini Split systems must always be properly sized to accommodate the indoor spaces they are designed to heat and cool.

Proper ductless mini split air conditioner and heat pump sizing is essential for high efficiency performance and the level of heating and cooling capacity. If the sizing is too small or too large, the system won't heat and cool properly, and it won't operate efficiently. And if the system is improperly sized, if the indoor units are mounted in the wrong locations, or the installation itself is done incorrectly, you'll be left with an expensive problem to fix. Ductless Mini Split air conditioner and heat pump systems that are incorrectly sized and improperly positioned can seriously interfere with humidity control and cost a bundle in high electric bills.

Sizing a split system will depend on many factors, the area you want to cool and on how many indoor air handlers you plan to include. The more indoor units you want, the more precise the sizing must be. Because you're investing in a high performance system we strongly recommend professional sizing and installation, that way, you'll know the job will be done properly and that your investment will be protected.

For every 12000 BTU an average of 600 square feet can be cooled or heated. If ductless mini split system produces 18000 BTU, the coverage improves to 900 square feet. Best case scenario means a square room with 8 foot ceilings, no windows in a climate of 72 degrees. Here are some of the variables that reduce the amount of square feet covered by a ductless a/c.

Six Variables that Reduce an Air Conditioners Useful Area:

  1. Climate: If you live in an area of the world that has seasonal temperatures in excess of 90° F. increase 30% or use our Climate HVAC calculator “Load Calculator”;
  2. Windows: If you have south facing windows in your designated area, or if you have large windows. Increase 20%
  3. Ceiling Height: High ceilings increase a room’s size reducing the air conditioners effectiveness. Increase 20%
  4. Appliances: Heavy kitchen appliances and electronics increase the heat created in an area. Increase 20%
  5. People: The more people in the area the more heat produced. Increase 20%
  6. Insulation: Poorly insulated homes are much more difficult to cool or heat. Increase 30%

Taking into consideration the above variables we can form a good estimation on the size of air conditioner needed to do the job. We know that 12000 BTU can cool 600 square feet or a room approximately 25’ x 25’. If any of the 6 variables from above are a factor, we will not be able to maintain a comfortable environment for your area. So we need to move up to a higher BTU ductless air conditioner.

For example, if our room is a 16’ x 16’ room (256 sq. ft.) in Orlando, FL (Increase 30%) with south facing windows (Increase 20%) you would need an air conditioner that can cool a 384 sq. ft. area.

Ductless mini split air conditioner and heat pump systems heat and cool a larger area at the same BTU level than do window air conditioners and portable air conditioners. There are only a few basic sizes produced in the ductless a/c industry:

  1. 9000 BTU – 450 square feet;
  2. 12000 BTU - 600 square feet;
  3. 18000 BTU - 900 square feet;
  4. 24000 BTU - 1200 square feet;
  5. 30000 BTU – 1500 square feet;
  6. 36000 BTU – 1800 square feet

If you come close to the max square feet numbers listed above after adding in your variables make sure to bump up to the next higher btu.