- Select the duct segment.
- In the Properties palette, under Dimensions, specify a routing preference and select the shape.
- Specify new sizes. You can manually select sizes or calculate them using the instant sizing tool:
To… then… calculate size for round duct accept the detected flow value for Flow Rate, or enter a flow value for Flow Rate. Click . 
The calculated duct size is displayed for Diameter.
calculate size for oval or rectangular duct based on a fixed height accept the detected flow value for Flow Rate, or enter a flow value for Flow Rate. Specify a size for Height, and click for Width.
You can change the height and recalculate the width repeatedly until you achieve a desirable duct size.
calculate size for oval or rectangular duct based on a fixed width accept the detected flow value for Flow Rate, or enter a flow value for Flow Rate. Specify a size for Width, then click for Height.
You can change the width and recalculate the height repeatedly until you achieve a desirable duct size.
- Click
.
- In the Modify Run dialog box, change the Routing preferences and other settings connected to the selected object.
- In the Maintain Connection dialog box, ensure a valid connection between the modified segment and the run:
Choose the appropriate action:
- Modify to maintain connection to next part.
Prompts you to add a transition fitting to connect the duct or fitting without changing the entire run.
- Modify to next junction/transition.
Resizes the branch to the next junction or transition. With this choice, the junction fitting that connects the 2 runs is replaced. The correct transition fitting is inserted in its place to maintain a valid connection at that junction.
- Modify to maintain connection to next part.