Powered makeup air shall be provided if the opening size exceeds which threshold in inches?

Powered makeup air shall be provided if the opening size exceeds which threshold in inches?

• A. 7
• B. 11
• C. 10
• D. 9

Answer: (B)

When ventilation exhaust could create a significant loss of indoor air, the building needs a controlled source of outdoor air. If the opening to the outside is larger than 11 inches, natural air leakage isn’t reliably enough to balance the exhaust, so a powered makeup air system is required to supply outdoor air and keep indoor pressure and combustion appliance operation safe. This helps prevent negative pressure, backdrafting, and related issues. For openings 11 inches or smaller, powered makeup air isn’t mandated. For example, a large 12-inch-wide intake would trigger the requirement, while a 9-inch opening would not.

When ventilation exhaust could create a significant loss of indoor air, the building needs a controlled source of outdoor air. If the opening to the outside is larger than 11 inches, natural air leakage isn’t reliably enough to balance the exhaust, so a powered makeup air system is required to supply outdoor air and keep indoor pressure and combustion appliance operation safe. This helps prevent negative pressure, backdrafting, and related issues. For openings 11 inches or smaller, powered makeup air isn’t mandated. For example, a large 12-inch-wide intake would trigger the requirement, while a 9-inch opening would not.