Flue gas travels through the fire box of a natural draft burner via which mechanism?

• A. Convection currents
• B. Radiation
• C. Conduction
• D. Diffusion

Answer: (A)

Convection currents drive the movement. In a natural draft burner, heating of the gases in the fire box makes them less dense, so the hot flue gas rises while cooler air is drawn in from below. This buoyancy creates a continuous convective loop that pushes gas through the fire box and up the chimney. Radiation and conduction describe heat transfer, not the bulk flow of gas, and diffusion is slow molecular mixing, not the sustained movement seen in natural draft systems.