Home Diffuser selection free tool HVAC Diffuser Selection Calculator HVAC Diffuser Selection Calculator Calculate required diffuser size, quantity, airflow per diffuser, velocity & throw check. Room Length (ft) Room Width (ft) Ceiling Height (ft) Total Airflow (CFM) Diffuser Type 300x300 (200 CFM) 450x450 (400 CFM) 600x600 (500 CFM) Noise Criteria NC 25 NC 30 NC 35 Calculate Results Facebook Twitter