CSLB C-39 Roofing ContractorFlashing, Ventilation and InsulationHard
A ventilated attic has a floor area of 2,000 square feet and will use a single powered attic ventilator instead of passive vents. Using the standard sizing guideline of 0.7 CFM per square foot of attic floor area, what minimum fan capacity should the ventilator provide?
- A2,000 CFM
- B700 CFM
- C1,400 CFM
- D1,000 CFM
Show answer & explanationAnswer & explanation
Correct answer: C. 1,400 CFM
Powered attic ventilators are commonly sized using 0.7 CFM per square foot of attic floor area. For 2,000 sq ft: 2,000 × 0.7 = 1,400 CFM minimum fan capacity, ensuring adequate air exchange without relying solely on passive intake/exhaust.
Why the other options are wrong
- A. This oversizes the fan beyond the standard guideline (1.0 CFM/sq ft).
- B. This equals only 0.35 CFM/sq ft, half the standard sizing guideline.
- D. This undersizes the fan for the given attic area.
Powered Attic Ventilator Sizing
Powered attic ventilators are typically sized at 0.7 CFM per square foot of attic floor area to ensure sufficient mechanical air exchange.
- Standard sizing: 0.7 CFM per sq ft
- Requires adequate soffit intake to match fan capacity
- Used as alternative/supplement to passive ventilation
Memory trick: Seven-tenths times the floor tells you what the fan's for.