HVAC
CFM Calculator
Calculate the airflow a room or system needs, by tonnage or by air changes per hour.
Result
Four hundred CFM per ton is the standard cooling design figure. Duct area assumes 700 feet per minute, typical for branch ducts. Trunk lines run faster and returns slower.
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About this calculator
How many CFM per ton?
About 400 for standard cooling. Humid climates sometimes design at 350 to improve dehumidification, and heat pumps in heating mode often want more.
What are air changes per hour?
How many times the room's entire air volume is replaced each hour. Six is typical for living space, while kitchens and bathrooms need considerably more.
The formula
CFM = tons × 400, or (room volume × ACH) ÷ 60
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