The mechanical ventilation for a crawl space of 3,000 square feet is

The mechanical ventilation for a crawl space of 3,000 square feet is

• A. 60 CFM
• B. 30 CFM
• C. 90 CFM
• D. 120 CFM

Answer: (A)

The key idea is that crawl-space ventilation is set by the crawl-space floor area, using a guideline of about 1 CFM per 50 square feet. For a crawl space of 3,000 ft², you divide by 50: 3,000 ÷ 50 = 60 CFM. This rate provides a steady flow of outdoor air to dilute moisture and keep humidity in check in the crawl space, helping to prevent mold and wood rot. Using a much smaller rate would under-ventilate the space (not addressing moisture adequately), while a much larger rate would be excessive for this area. In this case, 60 CFM aligns with the common rule, making it the appropriate choice.

The key idea is that crawl-space ventilation is set by the crawl-space floor area, using a guideline of about 1 CFM per 50 square feet. For a crawl space of 3,000 ft², you divide by 50: 3,000 ÷ 50 = 60 CFM. This rate provides a steady flow of outdoor air to dilute moisture and keep humidity in check in the crawl space, helping to prevent mold and wood rot.

Using a much smaller rate would under-ventilate the space (not addressing moisture adequately), while a much larger rate would be excessive for this area. In this case, 60 CFM aligns with the common rule, making it the appropriate choice.