The minimum soldering distance from plastic to metal compression on a hydronic line is 18 inches.

• A. 18 inches
• B. 12 inches
• C. 24 inches
• D. 30 inches

Answer: (A)

Heat management is the key here. When you solder metal piping near plastic on a hydronic line, the torch heat can travel along the metal and into the plastic or its insulation. That heat can soften or warp plastic, weaken fitting adhesives, or damage the insulation jacket, which risks leaks and system failure. Maintaining a safe clearance prevents this damage, and 18 inches is the standard minimum distance to keep the plastic protected while you work on the metal side. If you’re closer than that, you’re increasing the chance of heat-related damage. In practice, you’d either keep that gap or use heat shields and alternate methods to avoid exposing the plastic.