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

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

• A. 50%
• B. 25%
• C. 0%
• D. 75%

Answer: (B)

When makeup air is brought in through a metal louver, the louver itself creates resistance and reduces the actual air that makes it into the space. To account for this loss, NFPA 54 allows a 25% reduction in the calculated makeup air. In practice, you take the required makeup air and multiply by 0.75. This reflects the typical pressure loss and reduced free area of a metal louver, so the space still receives adequate air for combustion. If more precise data on the louver’s resistance were available, you could adjust further, but the standard approach uses this 25% reduction as a conservative rule of thumb.

When makeup air is brought in through a metal louver, the louver itself creates resistance and reduces the actual air that makes it into the space. To account for this loss, NFPA 54 allows a 25% reduction in the calculated makeup air. In practice, you take the required makeup air and multiply by 0.75. This reflects the typical pressure loss and reduced free area of a metal louver, so the space still receives adequate air for combustion. If more precise data on the louver’s resistance were available, you could adjust further, but the standard approach uses this 25% reduction as a conservative rule of thumb.