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HVAC School - For Techs, By Techs

Apr 12, 2018

In today's podcast episode, we talk with system and duct design educator Jack Rise about ACCA Manual J load calculation and Manual S system selection.

Many people know about Manual J, but relatively few techs follow it properly. When people attempt to do Manual J calculations, many of them go wrong when they overestimate the difficulty of the equations in Manual J. However, many of these techs do better when they can use software like Wrightsoft to help with their load calculations. The best way to approach load calculations is to develop confidence in software programs and field experience (sizing equipment and sealing ductwork); you are more likely to make mistakes if you put all of your confidence in one or the other. Some techs also don't take the time to measure buildings properly if they are either over-reliant on technology or too confident in their field skills.

Manual S is all about equipment selection after the load calculation. However, much of the manual is not useful for fieldwork. The rules are also not as regionally thoughtful as they could be, especially regarding furnace sizing and the consequential heat loss. Manual S is only useful if you perform a Manual J calculation first and use that result as a guide. Rise does not believe that Manual S is bad, but he thinks it gives installers way too much leeway on sizing as it stands.

Jack and Bryan also discuss:

  • Wrightsoft
  • Manual J practices in different types of buildings
  • Envelope leakage in retrofit applications
  • Most important chapters of Manual S
  • Accounting for sensible and latent heat load
  • New ventilation requirements
  • Odors, cooking, and building design
  • Increasing airtightness in building construction
  • Encapsulated attics

Learn more about ACCA standards and codes at

Learn more about Wrightsoft HERE.

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