Which statement correctly describes makeup air in relation to building pressure?

• A. Negative pressure in the building can contribute to makeup air deficiency
• B. Positive pressure always ensures adequate makeup air
• C. Makeup air is unaffected by building leakage
• D. Mechanical ventilation is not related to makeup air

Answer: (A)

Makeup air is the outside air brought in to replace air that’s being exhausted or leaking out of a building. Building pressure matters because when a building becomes negatively pressured (air leaving the building exceeds air entering), the system must supply enough makeup air to neutralize that loss. If the makeup air volume is not enough, the deficiency shows up: air is drawn in through cracks and unintended leaks rather than through the designed makeup air path, and the building remains or becomes under-pressurized. This can lead to drafts, unwanted infiltration of outdoor air, and even backdrafting of combustion appliances. Positive pressure can reduce inward leakage, but it doesn’t automatically guarantee adequate makeup air if the supply isn’t properly sized or controlled. So, negative pressure can contribute to makeup air deficiency because it increases the demand for makeup air beyond what the system provides.