The most important factors to consider when using the duct sizing tools are that the ducts form part of a system and that this system should have a nominated name that suits your design (not a default), which is created at the same time as the system being created. The system must also have a valid airflow, so either you specify the airflow of the air terminals or that flow is specified from the space and volume calculations.
Use the Tab key to select your system, as shown in Figure 10.31.
Figure 10.32 shows the Duct/Pipe Sizing tool located on the ribbon. This button becomes active when you select a single duct or duct run that is part of a fully enclosed system whose components are connected properly in regard to flow direction. Clicking the button opens the Duct Sizing dialog box. Figure 10.33 shows its available options.