Methodology guide
Volume, ACH, grill and electrical notes.
Calculator
Drum fan CFM calculator
Enter room L×W×H and ACH. Get the smallest 20, 24, or 30 in drum-fan CFM class or NO_MATCH.
Result
Required CFM ≈ (L × W × H × ACH) ÷ 60. Classes: 20 in / 4,800 · 24 in / 7,500 · 30 in / 12,000. Worked check: 20×25×10 @ ACH 8 → 667 CFM → 20 in class.
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