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Sizing a Ductless Mini Split Air Conditioner

Thursday, April 10, 2014

Let a pro size your ductless mini split for best performance.A ductless mini split offers substantial energy efficiency along with providing ample comfort, but only if it's the right size for the space you need to cool. Simply going by the square footage of that space can be misleading, since more factors come into play. Most HVAC contractors use software called Manual J to accurately size cooling and heating systems. 

Why Size Matters

If it's not properly sized, the system will increase your energy bills, won't do a good job of cooling or heating your space, and will have a shorter system life. The best way to size a dustless mini split is to work with your HVAC contractor rather than trying to do it yourself. However, you can use these guidelines to get an idea of how large it should be, based on these factors:

  • Baseline sizing. Each ton of the mini split system, or 12,000 BTUs (British thermal units), can handle 600 square feet. 
  • Climate. Hotter climates require more tonnage for cooling. If yours is routinely over 90 degrees, increase the tonnage by 30 percent. 
  • Windows. South and west windows, single-pane or large windows increase the cooling load. Add 20 percent to the baseline size of the ductless mini split to handle solar heat gain.
  • Heat-producing appliances. If the mini split will be cooling an area close to heat-producing appliances, add 20 percent.
  • Occupancy factors. People emit heat constantly, and if a lot of people will be using the space, increase the size by 20 percent.
  • Insulation and air infiltration. Inadequate attic insulation, poorly fitting windows, or significant air leaks throughout the space you're cooling will add to the heat gain. The size of the mini split should be increased by 30 percent.

Play it Smart: Call in a Pro

Misjudging the size of the mini split could result in an oversized system that will run in short cycles, which increases system wear, drives up energy consumption and leaves behind humidity. When HVAC systems first start, system stress is higher, and they use more energy than when they're running in mid-cycle. Too small a unit won't be able to handle extreme temperatures for your climate. That's why it's always advisable to consult a knowledgeable HVAC technician when choosing, sizing or installing new equipment.

For more information about a ductless mini split, contact Mitsubishi Electric to find a contractor near you today. 

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