Room CFM Calculator

Calculate the required airflow in CFM for each room based on room size, BTU load, and temperature difference.

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Visualization

How It Works

CFM stands for cubic feet per minute and measures the volume of air flowing through your HVAC system. Each room needs a specific amount of airflow to maintain its target temperature. The formula CFM = BTU divided by (1.08 times the temperature difference) comes from the physics of air: 1.08 is the heat capacity of air at standard conditions. If your supply air is 55 degrees and your room is 72 degrees, that 17-degree difference determines how much air you need to move. Too little airflow and the room stays warm. Too much and you get cold drafts. The number of supply registers in each room should match the CFM requirement.