A residential ventilation fan delivers 120 cfm while running for 30 minutes each hour. Ignoring startup effects, what is its hourly average flow?
- A30 cfm
- 60 cfm
- C120 cfm
- D240 cfm
Where to look it up
Explicit exercise assumptions; not a universal code requirement.
Why B is correct
120 × 30 / 60 = 60 cfm averaged over an hour. Average volume alone does not establish that intermittent operation meets an applicable ventilation standard.