How to Install a Dielectric Union on an Electric Water Heater

Electric water heaters are sometimes plumbed with piping constructed of two different materials, usually galvanized steel and copper. This can occur when new heaters are installed in homes with older plumbing systems. Joining the two pipes can create a phenomenon known as electrolysis. Electrolysis is a chemical reaction caused by the flow of electrical current between the dissimilar metals, and over time it may cause corrosive damage to the piping. Install a dielectric union to prevent electrolysis.

  1. Wrap a layer of pipe sealing tape over the threads of the galvanized steel water pipe. Wind the tape in a clockwise direction, overlapping each turn approximately 50 percent.

  2. Install the threaded end of the dielectric union onto the galvanized pipe. Turn the union clockwise and tighten with a pipe wrench.

  3. Slide the union nut over the end of the copper pipe with the open threaded end facing out.

  4. Score 2 inches of the end of the copper pipe with steel wool. Clean any existing burrs from the inside of the pipe lip with a reamer.

  5. Install the brass union end onto the copper pipe. Be sure that the pipe is fully seated inside the brass end.

  6. Sweat-solder the brass end to the copper pipe using a propane torch, acid-free flux and lead-free solder. Allow the pipe to cool.

  7. Install the plastic insulator over the brass end of the union. Slide the union nut forward and turn it clockwise over the threaded union end on the galvanized steel pipe. Tighten using the pipe wrench.


  • Wear safety glasses when soldering and be sure to work in a well-ventilated space.

About the Author

Max Stout began writing in 2000 and started focusing primarily on non-fiction articles in 2008. Now retired, Stout writes technical articles with a focus on home improvement and maintenance. Previously, he has worked in the vocational trades such as automotive, home construction, residential plumbing and electric, and industrial wire and cable. Max also earned a degree of biblical metaphysician from Trinity Seminars Ministry Academy.