When installing single wall metal flue pipe, what is the proper clearance from combustibles construction?

• A. 12 inches
• B. 6 inches
• C. 18 inches
• D. 24 inches

Answer: (B)

Clearance between vent piping and combustibles is required to keep heat from the pipe from igniting nearby materials. For single-wall metal flue pipe, the minimum distance from any combustible construction is six inches. This spacing helps prevent heat transfer to wood framing, insulation, or other combustibles, especially when venting runs are long or under higher flow. If the pipe passes through walls or ceilings, use a listed thimble, firestop, and shielding to maintain that clearance and protect the structure. Local amendments or manufacturer instructions may change specifics, but six inches is the standard minimum for this configuration.