New Air Conditioner? Sizing Guide

New Air Conditioner? Sizing Guide

New Air Conditioner? Sizing GuideWhen you’re in the market for a new cooling system, nothing is quite as important as the air conditioner sizing process you’ll go through with your HVAC contractor. Cooling systems aren’t a one-size-fits all appliance. Much of how they’re sized depends on the energy efficiency of your home first, and its actual size second.

The Process

Reputable HVAC contractors use Manual J software to run the sizing calculation, also called a load calculation Manual J requires the following elements of your home in order to calculate the optimal A/C capacity:

  • Insulation levels in the attic and walls.
  • Number of windows, their sizes, placement and orientation to the sun.
  • Air infiltration rates.
  • Cubic footage to cool.
  • Floor plan design.
  • Number of heat-producing appliances indoors.
  • Landscaping factors.
  • Temperature preferences, family size and ages.

The process will take time and it has to be done at your home. The HVAC pro will measure your windows, calculate the cubic footage and inspect the insulation levels. He’ll ask you questions about your family’s preferences and lifestyles for cooling.

Once all the data are input, the software returns a sizing recommendation. The next step is to use

Manual J’s sister software, Manual D, to properly size the ductwork to match the new air conditioner.

The Value of Sizing HVAC Equipment

Air conditioner sizing is so important because equipment that’s not the ideal size won’t run as efficiently. In our climate, a system that’s too large will increase energy costs and leave excessive humidity behind. One that’s too small won’t keep your home comfortable during periods of extreme heat.


Ductwork that doesn’t match the air conditioner will be noisy if it’s too small and ineffective if it’s too large. When air goes through a space that’s tight, it whistles. When there’s too much capacity in the duct, it won’t blow through forcefully enough.


When you’re replacing your cooling system, taking the time to go through the air conditioner sizing exercise will pay you back in greater comfort and lower energy bills. To learn more, contact Powers Heating & Air, providing HVAC services for Peachtree City homeowners.


Our goal is to help educate our customers in Peachtree City, Georgia and surrounding areas about energy and home comfort issues (specific to HVAC systems). For more information about other HVAC topics, download our free Home Comfort Guide or call us at 770-487-2040.

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