Manual D® Residential Duct Design

Technical Manuals
Manual D®

Manual DManual D® - Residential Duct Systems [ANSI/ACCA 1 Manual D - 2016]

The Third Edition of the ANSI-recognized Manual D: Residential Duct Systems will help you design a duct system in less time. This new edition includes updated and expanded VAV guidance, with detailed examples; impacts of excess length, sag, and compression in flexible ducts; new equivalent length values for flex duct junction boxes; and additionally identifying normative requirements in related informative material. Manual D, from the Air Conditioning Contractors of America (ACCA), provides a single set of ANSI-recognized duct sizing principles and calculations that apply to all duct materials.


The newly released Manual D has been significantly revised to include:

  • Updated and expanded VAV guidance, with detailed examples.
  • Impacts of excess length, sag and compression in flexible ducts.
  • New equivalent length values for flex duct junction boxes.

Manual D consists of three normative sections, thirteen sections, and seventeen appendices that assist in procedures and regulations surrounding residential duct systems.

Normative Content of Manual D

  • Section N1 - Normative Requirements
    This section includes the engineering calculations that are listed in Manual D, alongside mandatory duct system features and attributes. Manual D calculation tools, such as worksheets and third-party software, are also included, with instructions pertaining to proper use as well. Prohibited practices are also listed.
  • Section N2 - Manual D Worksheets
    This section includes detailed instructions for the proper usage of Manual D worksheets, alongside a set of blank worksheets. 
  • Section N3 - Normative Tables
    This section includes several informational tables, N3-1 and N3-2. These tables provide maximum air velocity values for duct airways, supply air grilles, return air grilles, and door undercuts for returning air.
  • Section N4 - Fitting Equivalent Lengths
    The final normative section provides the default fitting length values regarding equivalent feet of straight duct. These values provide input data for the Effective Length Worksheet.

Normative Content of Manual D

  • Sections 1 and 2 - Basic Duct Sizing Principles and System Operating Point
    The first two sections detail duct system physics, duct airflow, blower airflow, and the interactions between a given blower and a given duct system.
  • Section 3 - Blowers
    This section pertains to blower performance, blower motors, and performance pertaining to altitude.
  • Section 4 - System Performance Issues
    This section is about duct system physics and the relationship to pressure drops of varying types of system components. The use of structural framing for duct airways and the usage of a door undercut for a return air path is also covered.
  • Section 5 - Air Distribution System Design
    This section provides an executive overview of duct system design procedures, additionally covering the use of a branch take off fitting at the end of a supply air trunk duct.
  • Section 6 - Duct Sizing Calculations
    This section covers the duct system design procedures in detail. These procedures are embedded in the Manual D worksheets. This section also explains why balancing air dampers is required.
  • Section 7 - Air Zoned Systems
    This section goes over the procedures that apply to single-zone constant Cfm systems and to air-zoned systems, also covering that some air-zoned systems have unique problems. This section defers information to ACCA's Manual ZR, for details regarding duct system design for air-zoned systems.
  • Sections 8 through 13 - Examples Problems Demonstrating the Use of Manual D for Various Applications
  • Section 8 - Sizing Rigid Constant Cfm Duct Systems
  • Section 9 - Sizing Flexible Constant Cfm Duct Systems

Manual D Appendices

  • Appendix 1 - Tables and Equations
  • Appendix 2 - Friction Charts, Duct Slide Rules and Shape Equivalency Tables
  • Appendix 3 - Fitting Equivalent Length Concept
  • Appendix 4 - Fitting Equivalent Length Adjustments
  • Appendix 5 - Terminology
  • Appendix 6 - Duct Construction Standards
  • Appendix 7 - Standard of Care and Continuity
  • Appendix 8 - Residential Air Distribution Systems
  • Appendix 9 - Equipment and Air-Side Components
  • Appendix 10 - Duct System Efficiency
  • Appendix 11 - Duct Leakage and System Interactions 
  • Appendix 12 - Air Quality Issues
  • Appendix 13 - Noise
  • Appendix 14 - Testing and Balancing
  • Appendix 15 - Air Velocity for Ducts and Grilles
  • Appendix 16 - Excessive Length and Sag In Flexible Duct
  • Appendix 17 - Symbols and Abbreviations 


Additional Manual D Resources

ACCA Speed-Sheets

ACCA Speed-Sheets are Excel spreadsheets available for purchase that can be used in conjunction with ACCA Technical Manuals, which assist in learning important system design concepts. Speed-Sheets are not a replacement for the full Technical Manual, and are not a replacement for ACCA-approved software.

Learn more about ACCA's Speed-Sheets

Video Resources

Primer for using an ACCA Manual D Speed Sheet:

HVAC Essentials - Understanding Manual D

Approved Software

ACCA has approved software that works in conjunction with regulations, tables, procedures and worksheets that appear in Manual D.

Learn more about ACCA's Approved Software

ACCA Members-Only Resources

Get connected to your National HVACR Community.

ACCA Membership gives you access to a wide variety of exclusive HVAC resources, including hundreds of hours of exclusive webinars, informational videos, access to downloadable templates, articles, and customizable marketing materials.

Learn more about becoming an ACCA Member »

Members-Only Manual D Resources

Design Essentials - Manual D Residential Duct Systems Overview
This informative video by Ed Janowiak, Manager of HVACR Design Education, goes over all of the intricate details of residential duct systems detailed in Manual D.

Predictable Comfort - Manual D
Need 10 minutes or less to catch-up on Manual D? This episode of ACCA's Predictable Comfort briefly goes over Manual D, including how to find Friction Rate, and how to use the Duct Slide.

Predictable Comfort - Manual D Fundamentals: Long Circulation Path vs. Short Circulation Path
Need 10 minutes or less to catch-up on Manual D? This episode of ACCA's Predictable Comfort briefly goes over the circulation path calculations found in Manual D.

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