In the natural draft system, which component regulates the rise of flue gas?

• A. Stacked damper
• B. Temperature transmitter
• C. Burners
• D. Draft inducer

Answer: (A)

Natural draft relies on buoyancy to pull hot flue gases up the stack, and the strength of that draft is controlled by the resistance the gases meet in the stack. A stack damper is a movable plate in the stack that opens or closes to increase or decrease this resistance, dialing in the amount of draft. When you need to limit excessive draft, you partly close the damper; when more draft is required, you open it. The temperature transmitter simply measures flue gas temperature and doesn’t actively adjust the draft. Burners provide the heat but don’t regulate the rise of the gases. A draft inducer is a fan used in mechanical (induced) draft systems, not natural draft, so it isn’t the regulator in this setup.