Joints between different metallic piping materials in hydronic systems shall be made with what fittings?

• A. Standard Threaded Fittings
• B. PVC Unions
• C. Compression Fittings
• D. Approved Dielectric Fittings And Brass Converter Fittings

Answer: (D)

The joints between different metallic piping materials in hydronic systems must use fittings that prevent galvanic corrosion by electrically isolating the metals. Dielectric fittings do this with a non-conductive barrier between the two metal sections, stopping the electrical path that drives corrosion. Brass converter fittings also provide a safe transition between dissimilar metals, reducing galvanic action while allowing a reliable connection.

Using standard threaded fittings simply joins metals without isolation, which can allow galvanic corrosion. PVC unions aren’t suitable for metallic hydronic piping connections in typical hot-water or steam service due to temperature/pressure limits and compatibility issues. Compression fittings don’t inherently isolate dissimilar metals and thus don’t reliably prevent galvanic corrosion.