Intro to ACCA Manual T

Ed Janowiak joins the podcast to introduce us to ACCA Manual T.

Compared to other manuals, Manual T is one of the least-considered ACCA manuals. However, it’s the manual that advises us on how not to blow high-velocity air on people and has maintained the same standards since the mid-1900s. Unlike Manuals J, S, and D, Manual T is not recognized in code compliance.

Manual T deals with air distribution; it helps us find out the throw and spread, which informs our ductwork design in Manual D. We need to know the customer’s expectations and the air velocity we’ll need to manage at the registers before designing the ductwork. Register placement is also a critical element of Manual T.

Throw and spread can vary wildly, and register selection and placement are going to have a significant effect on comfort as a result. Register placement on the ceiling may achieve the Coanda effect to assist with air distribution, and that can be especially useful in low-load or passive homes. Low-load homes are an interesting case, as they use less hardware than other homes, meaning that we need to make the most of calculations and equipment selection.

Manual T ultimately focuses on using the diffusers and registers, rather than the equipment, to spread air throughout a space. Knowledge of the principles in Manual T also allows us to communicate, establish, and manage expectations with the customer.

Ed and Bryan also discuss:

  • Registers, diffusers, grilles, and vents
  • Filter restrictions
  • ACCA Manual LLH
  • Air movement in the occupied vs. unoccupied zone
  • Manual T as an extension of Manual D
  • What it means to lend credibility in this industry
  • Floor vs. ceiling registers based on climate


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