Which formula is used to calculate the CFM based on BTU/hr output?

The formula to calculate the airflow in cubic feet per minute (CFM) based on the output in BTUs per hour (BTU/hr) incorporates the specific heat of air and the temperature difference (TD) between the supply air and return air.

The correct formula, relating CFM to BTU/hr, is derived from the principle that the amount of heat delivered to the air can be determined by multiplying the CFM of the air by the heat content of the air. In this scenario, 1.08 represents the constant that combines the density of air (0.075 lb/ft³) and the specific heat of air (0.24 BTU/lb°F) for calculations at standard conditions.

When using the formula x = BTU/hr.Output / (1.08 x TD), it demonstrates how to find the required airflow in CFM to support a given BTU output while factoring in how much the air temperature will change (TD). This highlights the relationship between heating capacity and airflow, ensuring adequate heat transfer is achieved.

This formulation is crucial for HVAC professionals to ensure that they size and operate HVAC systems correctly, maximizing efficiency and comfort in heating applications.