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Blog Title: What is manual D?

Main Que: What is manual D?

  • Category:
  • Query By: Henry Jones (Austin, TX)
  • Date: 09/13/2016

Answer: Duct installers consult manual D for calculating size and to designing duct layout. The manual D takes into considerations factor such as length of the duct, its shape, and the material with which duct is made. It considers the blower speed, temperature, and output pressure of the HVAC unit. It also takes into account the number of branches from the main trunk, the fittings, elbows, curvature, and general symmetry, all of which have a big influence of duct size. The system's static pressure filters, and coils have a role on the friction rate. When sizing the duct it should kept in mind that size should compensate for loss in airflow due to friction over the length of the duct. Today Manual D software is available in which the desired CFM with the final friction rate is entered. The software displays the duct sizes for best performance and efficiency.

  • Replied By: Jack Williams (Austin, TX)
  • Replied Date: 09/20/2016