Natural draft what is it?

• A. Flue gas rises naturally and it's controlled by a stacked damper
• B. Flue gas is forced by a fan
• C. Flue gas is cooled by water injection
• D. Flue gas is recirculated through a blower

Answer: (A)

Natural draft relies on buoyancy: hot flue gases rise through the stack on their own because they are less dense than the surrounding air. A stacked damper provides a way to regulate that natural flow without introducing a fan or blower. The description that flue gas rises naturally and is controlled by a stacked damper matches this mechanism exactly.

Using a fan or blower would be mechanical draft, not natural draft. Water injection cooling changes the gas temperature and conditions but doesn’t describe how the gas moves in the stack. Recirculating gas through a blower also implies mechanical assistance, not natural rise.