What is the minimum clearance from the duct or exhaust fan to a noncombustible or limited interior surface?

What is the minimum clearance from the duct or exhaust fan to a noncombustible or limited interior surface?

• A. 4 inches
• B. 8 inches
• C. 6 inches
• D. 12 inches

Answer: (C)

Minimum clearance around a duct or exhaust fan to noncombustible or limited interior surfaces is six inches. This gap provides a safety buffer so heat, grease, or other buildup on the duct can’t easily transfer to nearby materials, helping prevent ignition risks while also giving space for inspection and maintenance. Even when the adjacent surface is noncombustible or only has limited fire resistance, keeping this six-inch distance is the standard requirement to maintain safe operation and service access. The other distances do not meet this minimum, so six inches is the correct measure.

Minimum clearance around a duct or exhaust fan to noncombustible or limited interior surfaces is six inches. This gap provides a safety buffer so heat, grease, or other buildup on the duct can’t easily transfer to nearby materials, helping prevent ignition risks while also giving space for inspection and maintenance. Even when the adjacent surface is noncombustible or only has limited fire resistance, keeping this six-inch distance is the standard requirement to maintain safe operation and service access. The other distances do not meet this minimum, so six inches is the correct measure.