Air Flow Calculator (CFM)
Our air flow calculator helps HVAC engineers and contractors design efficient ventilation systems. Calculate CFM requirements based on room size, determine proper duct dimensions, and ensure adequate air changes per hour.
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air ACH Requirements
volume_up Duct Velocity (FPM)
- 🔇 Quiet: 600-800 FPM
- 🔊 Branch: 800-1000 FPM
- 📢 Main: 1000-1200 FPM
The Formula
Air flow is measured in CFM. Higher ACH means more ventilation. Duct velocity should be 600-900 FPM for quiet operation, up to 1200 FPM for main ducts.
CFM = (Room Volume × ACH) / 60 or CFM = Velocity × Area
lightbulb Variables Explained
- CFM Cubic feet per minute
- ACH Air changes per hour
- V Velocity (ft/min or FPM)
- A Duct cross-sectional area (ft²)
tips_and_updates Pro Tips
Residential: 4-6 ACH, Commercial: 6-10 ACH, Industrial: 10-30 ACH
Keep duct velocity under 900 FPM for quiet operation
Main ducts can run 1000-1200 FPM
Branch ducts should be 600-800 FPM
Flexible ducts need larger size than rigid ducts
Account for fittings, filters, and coils pressure drop
Frequently Asked Questions
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All formulas verified against official standards.