To insert a supply arrow, go to
Ribbon: DM HVAC->Drafting-> 
Insert Supply Arrow
Pulldown Menu: DM HVAC->Drafting Tools->Insert Supply Arrow
You will be prompted to specify the insertion point for the tail of the supply arrow on the drawing.
Specify insertion point:
You will then be prompted to specify the rotation angle for the supply arrow.
Specify rotation angle:
The supply arrow will be inserted on the drawing.