There's no fixed number. A ducted heat pump typically has one supply vent per room or living area, though larger rooms or open-plan spaces sometimes have two to balance airflow. A home with eight rooms connected to the system will generally have around eight to ten supply vents, plus one return air grille where air is drawn back into the unit.The return air grille is usually a single point, most often a hinged panel in the hallway ceiling or a wall grille for subfloor systems, regardless of how many supply vents the system has.Every supply vent and the return grille should be checked and cleaned as part of a full professional service, since restricted airflow at one vent can affect the whole system's balance.