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Ductwork Calculations

The Ductwork Calculations command is used to calculate the airflow in ducts, size the ducts, and calculate the pressure loss in ducts.

To calculate these values in ducts, go to
Ribbon: DM HVAC→Ducts→  Ductwork Calculations
Pulldown Menu: DM HVAC→Calculations→Ductwork Calculations

Duct Calculations Dialog Box​

  •  🔘 Ducts to Use Controls the ducts on which the selected calculation will be performed.

    •  All Ducts Perform the selected calculation for all of the ducts in the project, including those on other drawings. This selection takes the most time.
    •  Ducts in a Branch Perform the selected calculation on the selected duct and all connected ducts leading to the diffusers. Connected ducts leading to the fan will not be included.
    •  Ducts in a System Performs the selected calculation on the selected duct and all connected ducts.

  •   Press this button to calculate the airflow in the selected ducts. The total airflow in CFM in all ducts will be updated. You can query the duct to view the airflow in each section. Nothing else is changed or calculated.

  •   Press this button to calculate the airflow in the selected ducts and size them based upon the newly calculated airflow. The total airflow in CFM in all ducts will be updated. You can query the duct to view the airflow in each section. The duct size and shape will be updated in the database and on the drawing.

  •   Press this button to calculate the airflow in the selected ducts, size them based upon the newly calculated airflow, and calculate the pressure in the ducts. The total airflow in CFM in all ducts will be updated. The duct size and shape will be updated in the database and on the drawing. The pressure drop in each section and the total pressure drop in the duct system will be calculated. You can query the duct to view the airflow and the pressure drop in each section.

Calculating Values​

After you select a calculation, the dialog box will close. You will be prompted based upon your 🔘 Ducts to Use selection.

All Ducts​

The selected calculations will start immediately. All of the ducts in the project will be included.

Ducts in a Branch​

You will be prompted to select the duct at the start of the run to be calculated.

Select duct or label at the start of the branch:

The calculation will be performed on the selected duct and all of the ducts between it and the diffusers.

Ducts in a System​

You will be prompted to select a duct in the system to be calculated.

Select duct or label in the system:

The calculation will be performed on the selected duct and all of the ducts connected to it.

Related Options

You can customize the fittings used when sizing ducts with this command. See the Default Fittings Options and Fittings Options sections for more information.

There are several options that affect default values, labels, and behaviors when sizing ductwork. See the Ductwork Options section for more information.