By Garry Stockton
Are you aware that you can develop your Duct run over the Grilles/Air Terminal and connect by simply selecting the terminal then the Duct?
Added Ductwork
Once your Grilles/Terminals are in place
Create your Duct Run
Select The Terminal,
Once the Terminal has been selected (In plan or 3D view), the ‘Layout’ panel appears on the Ribbon Bar. Choose ‘Connect Into’ then the Ductwork.
Select the overhead Duct and it connects automatically.
Note; Revit will throw up an alert if there are discrepancies in sizing.