Which statement is true about makeup air calculations for louvers?

Which statement is true about makeup air calculations for louvers?

• A. Metal louvers require a 75% reduction
• B. Wooden louvers require a 25% reduction
• C. Metal louvers require a 25% reduction
• D. Wooden louvers require a 75% reduction

Answer: (C)

Makeup air through louvers isn’t all usable space. The louver’s blades and frame obstruct some of the air passage, so you adjust the opening area with a reduction factor to reflect the actual air that can enter. The standard assigns different reductions based on material because the obstruction and flow characteristics differ: metal louvers are less obstructive, so a 25% reduction is used, leaving 75% of the gross opening as effective area. Wooden louvers are more obstructive, so a larger reduction is applied (75%), leaving only 25% of the gross opening effective. Therefore, for metal louvers, the makeup air calculation uses a 25% reduction, which is the best choice. For example, a metal louver with a gross free area of 100 square inches would have 75 square inches of effective area after the reduction.

Makeup air through louvers isn’t all usable space. The louver’s blades and frame obstruct some of the air passage, so you adjust the opening area with a reduction factor to reflect the actual air that can enter. The standard assigns different reductions based on material because the obstruction and flow characteristics differ: metal louvers are less obstructive, so a 25% reduction is used, leaving 75% of the gross opening as effective area. Wooden louvers are more obstructive, so a larger reduction is applied (75%), leaving only 25% of the gross opening effective. Therefore, for metal louvers, the makeup air calculation uses a 25% reduction, which is the best choice. For example, a metal louver with a gross free area of 100 square inches would have 75 square inches of effective area after the reduction.