The calculation used to supply makeup air through a wooden louver must be reduced by what percent?

The calculation used to supply makeup air through a wooden louver must be reduced by what percent?

• A. 25%
• B. 0%
• C. 75%
• D. 50%

Answer: (C)

When sizing makeup air through an opening like a louver, you must account for how much of that opening actually contributes to airflow. Louvers, especially wood ones, obstruct and redirect air flow, so the effective free area is much smaller than the nominal opening. For a wooden louver, the standard conservative adjustment is to reduce the calculated makeup-air flow by 75%, leaving only 25% of the calculated value as usable. This ensures the system remains capable of delivering enough combustion air even with the flow-impeding characteristics of wood louvers.

When sizing makeup air through an opening like a louver, you must account for how much of that opening actually contributes to airflow. Louvers, especially wood ones, obstruct and redirect air flow, so the effective free area is much smaller than the nominal opening. For a wooden louver, the standard conservative adjustment is to reduce the calculated makeup-air flow by 75%, leaving only 25% of the calculated value as usable. This ensures the system remains capable of delivering enough combustion air even with the flow-impeding characteristics of wood louvers.