HVAC
HVAC CFM Calculator
Work out the air flow a system or a room needs, in cubic feet per minute.
Result
400 CFM per ton is the common design figure, but it is a starting point. Humid climates often run 350 to remove more moisture, and heat pumps in heating mode want more. Measured static pressure, not a rule of thumb, tells you what a duct system is actually delivering.
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About this calculator
Why 400 CFM per ton?
It balances sensible cooling against moisture removal for a typical system. Running lower takes out more humidity at the cost of capacity; running higher does the reverse.
My system does not move its rated air.
Very common, and usually the ducts rather than the equipment. Undersized returns and long flexible runs both choke air flow, and the only way to know is to measure static pressure.
The formula
room CFM = volume x air changes / 60; system CFM = tons x CFM per ton
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