Duct Air Velocity (FPM) & Noise Criteria Grille Calculator
Calculate air face velocity (FPM and m/s), velocity pressure (Pv), and predicted Noise Criteria (NC sound rating) for supply diffusers, return grilles, and branch ducts to prevent objectionable airflow noise per ASHRAE Fundamentals.
Airflow & Grille Geometry
CFM
Inches
Inches
Effective Face Velocity
PREDICTED NC 28 (QUIET)
533 FPM
2.71 m/s (Velocity Pressure: 0.018 in. w.g.)
Predicted Sound Rating
NC 28
Suitable for residential living spaces
Effective Free Area (Ak)
0.375 sq ft
54.0 sq in net (from 72.0 sq in gross)
ASHRAE Design Recommendations
Airflow velocity is well-proportioned for standard residential living areas. To achieve silent bedroom comfort, consider enlarging the grille to 14"x6" to drop velocity below 450 FPM.