The Remove Label command is used to remove a duct label from the drawing. If you use the standard CAD ERASE command, the label will be reinserted when the 2D ductwork is redrawn.
To remove a duct label, go to
Ribbon: DM HVAC->Ducts-> 
Remove Label
Pulldown Menu: DM HVAC->2D Drafting->Remove Label
You will be prompted to specify the duct label to be removed.
Select label to remove:
The duct label will be removed from the drawing and will not be reinserted when the 2D ductwork is redrawn.