Single-wall metal flue pipe shall be supported according to which criterion?

• A. Based on indoor temperature
• B. For the design and weight of the material
• C. By the pressure rating only
• D. At every joint

Answer: (B)

The way single-wall metal flue pipe is supported is driven by the pipe’s own weight and its design. Heavier pipes or longer runs place more stress on supports, elbows, and joints, so the installation must provide adequate support to prevent sagging, joint separation, or damage from thermal movement. Temperature by itself isn’t the criterion, and the pressure rating isn’t the basis for how you space supports. Joints and fittings still need secure support, but the key factor is the weight per length and the design specs (often from the appliance manufacturer and NFPA 54). Always follow those design/weight requirements for proper support spacing.