What is a Load Calculation?

A load calculation is a method of determining the heat gain and loss of a home or building so that HVAC equipment is properly sized. A building’s heating or cooling design load is based on how well insulated the building is and in what climate it is located. It represents the amount of heating or cooling capacity that is needed during the coldest or hottest day of an average year to keep the interior of the space comfortable. 

Why are Load Calculations Important?

Properly calculating heating and cooling loads is necessary to choose the right heat pump. Skipping this step or using simple rules of thumb risks choosing the wrong sized heat pump which negatively impacts efficiency, performance, and customer satisfaction. Oversizing can lead to excessive cycling, low efficiency, shortened equipment life, and ineffective summer dehumidification. Undersizing can result in over reliance on backup heat, or inadequate summer cooling and increase energy costs.

Load Calculation Tools

The North American standard for proper sizing is set by the Air Conditioning Contractors of America (ACCA). Here are a few of the many free or for purchase load calculation tools. (Not all are certified by ACCA). 

Cool Calc Manual J Software 

BetterBuiltNW HVAC Sizing Tool

ServiceTitan HVAC Load Calculator

Kwik Model 3D - EnergyGauge Loads

Quality First Heat Loss & Heat Gain Software 

MiTek Wrightsoft Right-J®

Elite Software – Rhvac

Loadcalc.net - HVAC Load Calculator


The list of tools does not reflect an endorsement or assurance of quality by NEEP.

Always check with your local jurisdiction about code requirements for acceptable load calculations. 

Heat pumps should always be installed by licensed, trained professionals. Cold climate sizing and design training following these same principles can often be found through heat pump manufacturers and their distributors. Always follow manufacturer specifications and installation instructions, and all applicable building codes and regulations.

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