CFM Airflow Calculator
Room Ventilation CFM
Calculate required CFM for a room based on air changes per hour
CFM from Duct Velocity
Calculate CFM from duct size and air velocity
HVAC System CFM
Calculate CFM required for heating/cooling system
Formula
CFM = Volume x ACH / 60 | CFM = Duct Area x Velocity | CFM = BTU / (1.08 x Delta-T)
Frequently Asked Questions
How do I calculate CFM for a room?
CFM = (Room Volume x Air Changes per Hour) / 60. For example, a 20x15x8 room (2,400 cu ft) needing 6 air changes per hour: (2,400 x 6) / 60 = 240 CFM. Air changes per hour depend on the room type and usage.
What is a good CFM for HVAC?
For residential HVAC, the standard is 400 CFM per ton of cooling capacity. A 3-ton system needs about 1,200 CFM. For heating, 350-400 CFM per ton is typical. Too little airflow causes freezing coils; too much reduces dehumidification.
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