Use the System Editorto add the component to the existing system.
Verify that there is an open connector in the system where you are connecting components, and if necessary add a tee to a duct segment to provide the open connector.
Highlight one of the components in the existing system, and press Tab until a preview of the path from the added component(s) to the existing system displays.
Click Modify | Duct Systems tabLayout panel Generate Layout.