How to connect copper plumbing to plastic

Updated July 20, 2017

Copper pipes serve as one of the primary sources for water distribution in homes and buildings. With the advances in plastic alternatives, you may be considering switching your copper to crosslinked polythene tubing (PEX). While this plastic tubing is relatively easy to use and more easily routed than copper or PVC, connecting copper to PEX will take specific fittings and tools.

Use sandpaper to clean the end of the copper pipe and the copper end of the sweat adaptor. Be certain debris is removed after you finish sanding.

Use a flux brush to apply a generous amount of flux both to the outside of the copper pipe where the fitting will connect and to the inside of the fitting where it will connect to the pipe.

Slide the fitting on the end of the pipe until it stops. Light your torch and begin to heat the joint. This will cause the flux to liquefy when it is heated enough.

Begin applying solder by touching the end of the solder to the joint. Do this slowly, applying the solder one touch at a time. This will help to limit dripping and ensure that you are monitoring the flux well enough to know when the solder should be applied. Continue to do this until the entire joint has been sealed with solder. Check carefully for any missed spots or leaks before moving on.

Place a crimp ring over the end of the PEX tube. Slide it down the tube a couple of inches.

Push the barbed PEX end of the fitting into the end of the PEX tubing. Slide the crimp ring up the tubing until it covers the end of the fitting inserted into the tubing, approximately 1/8 inch from the end of the tube.

Use your crimp tool to crimp the ring down around the fitting. After you crimp the ring, use a PEX gauge to determine if the crimp fits into the "go" side of the gauge. If the crimp fits, you have successfully connected the fitting. If it does not, you will need to cut the crimp ring and attempt the crimp again with a new crimp ring.


Quick-connect fittings make an easy "push together" connection but are only for use on accessible connections. Colour-changing flux is available to make it easier to tell when the flux has reached the appropriate temperature.


Do not attempt to solder before cleaning the copper. The copper will be hot after soldering; do not touch.

Things You'll Need

  • PEX tubing
  • Copper piping
  • PEX-to-female sweat adaptor
  • PEX crimper
  • PEX crimp ring
  • Mapp torch
  • Mapp gas
  • Solder
  • Flux
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