Load Calculations – Understanding Manual J

An accurate load calculation is the first step and the cornerstone of proper design for residential structures. Every other step in the design process is dependent on a legitimate load estimate.

Software programs are available that make completing the load much simpler. However, many HVAC professionals struggle because they lack experience and understanding of the steps (i.e., process) used to complete a home load. They also struggle with making educated assumptions and developing reasonable defaults for the load software.

  • Our load program begins with a review of the different components that must be evaluated to complete a load calculation.
  • Home construction techniques and each load component are examined to illustrate their impact on home durability, indoor air quality, safety and energy efficiency.
  • Participants learn how heat transfer multipliers are created.
  • An overview of the features, sensitivities and limitations associated with the current (8th edition) and past versions (AE and 7th edition) of the ACCA Manual J is presented.
  • Participants complete a simple residential heating and cooling load calculation manually, using the procedures and reference tables within Manual J, 7th edition.
  • Infiltration and ventilation calculations conclude the load process. A block heating and cooling sensible heat load, a latent heat load, and sensible heat ratio for cooling are then calculated.
  • The load results that are used to select HVAC equipment are examined in detail.
  • Insight gained through this program can now be applied to selecting and/or using computer software-based load calculation programs more effectively in the future.


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