The proposed revisions are to the four Normative Sections of Manual D, which contains the minimum requirements for designing a residential duct system. Revisions were made in the following sections:

• N1: General Requirements and Definitions

• N2: Manual D Procedure

• N3: Maximum Air Velocity and Transfer Air Tables

• N4: Fitting Equivalent Lengths

Manual D uses heating and cooling loads to determine space air-delivery requirements for residential applications.

The Manual D procedures match duct system resistance (pressure drop) to blower performance (as defined by the HVAC system manufacturer’s blower performance tables). This delivers appropriate airflow to the rooms and spaces to be conditioned while ensuring that system airflow is compatible with the operating range of the HVAC equipment. The capabilities and sensitivities of the Manual D procedures are compatible with single-zone and multi-zone systems. The primary equipment may feature single-, multi-, or variable-speed blowers.

Manual D is also referenced by the International Code Council’s International Residential Code (IRC) and the International Association of Plumbing and Mechanical Officials’ Uniform Mechanical Code (UMC).

A copy of the proposed Normative Sections can be obtained by contacting David Bixby, ACCA manager of codes and standards, at david.bixby@acca.org. Comments on the revisions can be directed to Bixby as well.

For more information, please contact Kate Wessels, ACCA vice president of communications, marketing, and partnerships at kate.wessels@acca.org.