What Adapter For

How to connect PEX to galvanized pipe

Use a brass PEX x NPT adapter, with pipe thread on one end for the steel and a PEX end on the other. Adapters are named by both sizes, such as Uponor’s 1/2" PEX x 1/2" NPT.

What fits

A brass PEX x pipe thread adapter

On the package: PEX x NPT: female if the steel pipe has threads outside, male if it ends in a fitting

the codes join plastic pipe to other pipe with an approved adapter fitting

Available on Amazon

PEX x female NPT brass adapter PTFE thread seal tape

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  • Shut the water off and drain the line before you cut anything.
  • Brass PEX adapters come with male or female pipe thread (NPT) on one end. Pick the one that mates with the steel pipe’s end, and the PEX end that matches your PEX joints.
  • Wrap tape on the male threads before screwing the adapter on.
  • SharkBite’s instructions keep its push-to-connect fittings off galvanized pipe, and its Max guide rules out its threaded ends too.

Galvanized steel joins by thread and PEX by rings or crimps, so a brass adapter with one of each sits between them.

More: Connecting different pipe

Before you start

  • Make sure the steel pipe carries water. Gas pipe is threaded steel too. If you can’t trace the pipe to a faucet or fixture, leave it alone and ask a plumber.
  • Rusted fittings and rust-colored water, particularly from hot water lines, are signs of advanced deterioration in galvanized pipe.
  • If a lead service line ever fed this galvanized pipe, lead can cling to its inside and get into the water. Ask your water utility about testing.

Common questions

Do I need a dielectric union between PEX and galvanized pipe?

The codes ask for a dielectric or brass fitting where copper meets galvanized steel. PEX to steel falls under their plastic pipe rule instead, which asks for an approved adapter fitting.

Keep going

Connecting different pipeGalvanized to copperPipe thread sizeWhat pipe do I have?PEX to copperGarden hose to 1/2" pipeGarden hose to 3/4" pipe

For a different part on either end, open the adapter finder with this pair picked.

Where we get our information from

The sizes on this page come from published standards and the makers’ own documents. Checked against published data from International Code Council, Swagelok, SharkBite, US EPA and HUD (plus 1 more).

See all 7 sources
  • Swagelok, Thread Sealants catalog (MS-14-01): PTFE tape, how to apply
  • SharkBite (Reliance Worldwide), SharkBite Max Installation Guide (2023): approved pipe, depths, removal, burial, warnings
  • US EPA, Customer Guide for Identifying Service Lines (2024): scratch and magnet tests, galvanized downstream of lead
  • HUD, Residential Rehabilitation Inspection Guide (2000): water supply piping, fuel supply
  • Uponor, PEX Piping Systems Installation Guide, seventh edition (2025): ProPEX expansion fittings, pipe colors, copper and threaded adapters, no soldering within 18" of PEX
  • International Plumbing Code 2021, sections 605.23, 605.23.1 and 605.23.2: joints between different materials, copper to galvanized steel (as adopted in South Carolina)
  • International Residential Code 2021, sections P2906.18 and P2906.18.1-P2906.18.3: joints between different materials, PVC service to CPVC (as adopted in South Carolina)

General guidance from manufacturer and standards data. Parts vary by brand, so check the size printed on the package against what you measured. For gas lines or anything inside a wall, use a licensed plumber.