What is primary air?

• A. Air that cools equipment
• B. Air that externally supplied to the flame at a point of combustion
• C. Air that mixes gas before it hits the burner before combustion
• D. Outside air for general ventilation

Answer: (C)

Primary air is the portion of combustion air that mixes with the gas before combustion occurs, inside or at the burner, creating the premixed air–gas mixture that will burn. This premixed mixture determines flame stability, color, and efficiency, and is distinct from air used for ventilation or for secondary combustion. So the best description is air that mixes gas before it reaches the burner and before combustion.