Residential HVAC Installation Practice Exam

The correct answer is velocity pressure plus static pressure because duct pressure in a ventilation system is a combination of two components: velocity pressure and static pressure. Velocity pressure represents the kinetic energy associated with the air velocity in the duct, while static pressure represents the potential energy exerted by the air due to the ductwork's configuration and resistance. When these two pressures are added together, we get the total duct pressure in the system. Hence, the correct answer is C: Velocity pressure plus static pressure.