Which feature prevents backdraft in a chimney?

• A. Flue Lining
• B. Chimney Cap
• C. Draft Damper
• D. Smoke Chamber

Answer: (A)

Backdraft is caused by air moving down the flue or by gaps in the path that let outdoor air work its way into the chimney, pushing smoke back into the room. A flue lining creates a smooth, continuous, sealed channel inside the chimney. That smooth interior minimizes cracks, gaps, and irregularities in the masonry, so air can’t easily seep in or press down the flue. With the lining in place, combustion gases have a consistent upward path, reducing the chance that they’ll reverse direction and come back into the living space. It also protects the masonry from heat and moisture damage that could create leaks over time, which would otherwise create new routes for backdraft.

A chimney cap mostly shields the flue from rain and animals, and can influence wind patterns at the top but doesn’t by itself create the sealed, smooth passage that prevents reverse flow. A draft damper helps regulate flow but isn’t always present or sufficient on its own to stop backdraft in varying wind conditions. The smoke chamber’s role is to guide flow from the firebox into the flue, not to prevent backdraft by itself.