To insert a fire or smoke damper, go to
Ribbon: DM HVAC->Ducts-> 
Fire/Smoke Damper
Pulldown Menu: DM HVAC->Fittings->Fire/Smoke Damper
You will be prompted to specify the duct on which a fire/smoke damper is to be inserted.
Select duct or label to insert fitting at:
The Damper Type dialog box will appear.
Inserting a Vertical Damper
Press the Vertical Damper button to insert a vertical damper on the duct. The vertical damper will be inserted on the selected duct as shown below.
Inserting a Horizontal Damper
Press the Horizontal Damper button to insert a horizontal damper on the duct. The horizontal damper will be inserted on the selected duct as shown below.
