What is the minimum pressurization condition for HVAC ductwork relative to surrounding areas?

• A. Positive pressure relative to surrounding areas.
• B. Neutral pressure relative to surroundings.
• C. Negatively pressurized relative to the surrounding area.
• D. Pressure depends on outdoor weather.

Answer: (C)

The fundamental idea is controlling where air leaks go by using a pressure difference between ductwork and the spaces it serves. Keeping the ductwork slightly negative relative to surrounding areas means any leakage through joints or gaps will pull air from the room into the duct rather than push duct air out into the room. This helps contain contaminants and odors inside the ducted system and reduces the chance of ducts spreading air into occupied spaces.

If the duct were neutral, leaks could allow air to move in either direction, undermining containment. If the duct were positively pressurized, air would tend to escape from the duct into surrounding spaces, increasing energy losses and the potential spread of contaminants. Outdoor weather isn’t what sets this design; it’s the intentional pressure relationship chosen to maintain containment and IAQ.