After all diffusers are connected by routing line we are ready to use Duct Routing Tool. This tool reads entire network and converts it into actual ducting network. First Select the main unit or plenum which is the main source for ducting.
 

Tool will traverse all network  starting from the source and will calculate the total air quantity of all diffusers connected to it.

This  is shown under statistics in the main dialog box.

 Now its time to select the routing network which is to be converted into ducting. Click on the 'Select branch for Routing' button to proceed. Click on the routing line starting from the main unit or plenum. Make sure you click near the main unit or plenum end.