How to Calculate Furnace CFM

To calculate the CFM for a furnace, use the following formula:

CFM = BTUH OUTPUT / (1.08 × (SUPPLY AIR TEMP - RETURN AIR TEMP))

Where:

• CFM: Cubic Feet per Minute (airflow required)
• BTUH OUTPUT: British Thermal Units per Hour (output of the furnace)
• SUPPLY AIR TEMP: Supply air temperature in °F
• RETURN AIR TEMP: Return air temperature in °F
• 1.08: A constant that includes the specific heat of air and the density of air at standard conditions

Use the form above to input the values, and the calculator will provide the required CFM.

Reference

https://trutechtools.com/Measuring-Airflow-using-the-Temperature-Rise-Method_c_255.html