The formula to calculate the air flow rate requirement in a biomass furnace is:

\[ AFR = FCR \cdot S_a \]

Where:

• \(AFR\) is the air flow rate in kilograms per hour (kg/hr).
• \(FCR\) is the fuel consumption rate in kilograms per hour (kg/hr).
• \(S_a\) is the stoichiometric air requirement in kilograms of air per kilogram of fuel (kg air/kg fuel).