• In this video, This Old House plumbing and heating contractor Richard Trethewey explains how to join steel and copper pipes.


    1. Turn off water and power to water heater.
    2. Use garden hose to drain water from heater's tank.
    3. Cut copper pipe just above the corroded connection using a tubing cutter.
    4. Use two pipe wrenches to loosen the old union.
    5. Remove the old union from the steel pipe.
    6. Wrap threads on end of the steel pipe with Teflon tape.
    7. Install the lower half of the dielectric union to steel pipe; tighten first with pliers, then with pipe wrench.
    8. Solder coupling and small length of pipe to end of existing copper water pipe.
    9. Remove the rubber gasket from dielectric union.
    10. Solder top half of union to copper pipe.
    11. Allow union to cool, then replace the rubber gasket.
    12. Use wrench to tighten together the two halves of the union.
    13. Turn power and water back on, and check for leaks.
    • Difficulty: Moderate
      Requires a little soldering, but the real challenge is muscling out the corroded fittings without breaking a pipe - or knuckle

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      Video Directory

      Selected Topic/Section

      Tools List

      • propane torch
        Propane torch
      • tubing cutter
        Tubing cutter, used to cut copper tubing
      • needlenose pliers
      • pvc pipe cutter
        Pipe wrenches

      Shopping List

      1. Dielectric union

      2. Copper pipe and coupling

      3. Emery cloth
      used to clean outside of pipe ends prior to soldering

      4. Flux

      5. Lead-free solder

      6. Teflon pipe tape
      used to produce watertight seal at threaded pipe

      7. Garden hose
      used to drain water heater