Duct Design (Manual D)

Manual D: Duct Design

Once the load calculation tells you how much air each room needs, Manual D determines how to actually deliver it. This is the engineering behind the ductwork itself — sizing every trunk and branch run so airflow is balanced, static pressure stays within the system's design limits, and every room gets the air it was designed to get.

Manual D duct design addresses:

• Proper trunk and branch sizing for correct CFM to every room

• Static pressure calculations matched to the equipment's blower capability

• Duct material and routing selection

• Return air pathways and balance

• Elimination of the airflow guesswork that causes hot and cold rooms

Why it matters:

Even a correctly sized system will underperform if the ductwork moving that air is undersized, oversized, or poorly routed. Poor duct design is one of the most common — and most overlooked — causes of comfort complaints, high utility bills, and premature equipment failure. Manual D turns the load calculation into a buildable, code-compliant duct layout instead of a rule-of-thumb install.

What you get:

A full duct design package built from your Manual J results, using professional software for accurate modeling. Includes trunk and branch sizing, static pressure verification, and a layout your installers can build directly from.

Who This Is For

These are precision engineering services offered independently of installation work — built for HVAC contractors, builders, and designers who need accurate, code-compliant documentation without adding it to their own workload. It can also be for home owners who are tired of the guesswork. Whether you need a single calculation for a permit submission or a full design package for new construction, Charleston Ductworks delivers fast turnaround backed by on-site LiDAR scanning for accuracy you can build from with confidence.