How to Connect PEX to Copper Pipe

Cross-linked polythene pipe (PEX) is a viable alternative to copper piping for plumbing purposes. PEX is economical, easy to install, lightweight, and flexible. PEX plumbing installations require fewer fittings than rigid copper installations. For example, the piping can be unrolled from 100m spools and installed in long runs without in-line pipe couplings. It can also turn 90-degree corners, requiring fewer right-angled elbow fittings when compared to copper pipe installations. PEX withstands freezing and is not prone to "water hammering". It can be readily connected to existing copper piping without using glue, solder or corrosive flux.

Measure the required length of PEX pipe using a steel tape measure and mark with a fine felt tipped pen. Use the specially designed PEX tubing cutter and cut to length; this tool will hold the pipe at a right angle to the blade, and produce a clean square cut.

Cut the copper pipe to the correct length with a standard pipe cutter. This consists of a 'G' frame with a hardened cutting wheel mounted opposite a pair of adjustable rollers. The tube is clamped between the rollers and the cutting wheel, and then revolved around the pipe. After each turn the rollers are tightened with a knurled adjusting knob until the wheel cuts through the pipe; this produces a clean, right angle cut.

Remove the burr left by the pipe cutter on the inside edge of the copper pipe with some rolled up 120-grit emery paper. Smooth off any remaining irregularities on the face of the cut.

Use your tape measure and felt tipped pen to mark off exactly one inch from the recently cut ends of both the PEX and the copper pipes.

Hold the copper pipe firmly with one hand and insert the end into the PEX push-fit straight coupling. Push the coupling home until it can't go any further. Check to see that the end of the coupling is in line with the pen mark on the copper pipe.

Repeat by inserting the cut end of the PEX piping into the other end of the push-fit coupling. Grip the coupling with one hand and press the PEX pipe firmly in until it encounters resistance and lines up with the 1-inch mark.

Connect the other end of the PEX pipe to complete the PEX to copper connection and turn the water on. Check for leaks. Water dripping from either end of the in-line coupling can only be caused by one of two factors: Irregularities on the end of the pipe, or by poor contact with the coupling seal.

Slot the U-shaped disconnect clip over the pipe and press it against the coupling. Remove the pipe and clean up any ragged edges with 120-grit sandpaper. Double check the 1-inch measurement and push the pipe firmly back into the coupling until it encounters resistance, and the mark lines up with the edge of the coupling. Test for leaks.


Use blue PEX pipe for cold-water plumbing and red PEX pipe for hot-water plumbing.


If you are connecting PEX tubing to any appliance with ferrous (iron based) components or castings, such as hot water manifolds, you must use PEX tubing with a built in oxygen barrier. Standard PEX tubing will cause ferrous fittings to rust. Do not expose PEX tubing to sunlight for prolonged periods.

Things You'll Need

  • Steel tape measure
  • Fine felt-tipped pen
  • PEX tubing cutter
  • Standard pipe cutter
  • 120-grit emery paper
  • PEX push-fit straight coupling
  • U-shaped disconnect clip
Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

After graduating from the University of the Witwatersrand and qualifying as an aircraft engineer, Ian Kelly joined a Kitchen remodeling company and qualified as a Certified Kitchen Designer (CKD). Kelly then established an organization specializing in home improvement, including repair and maintenance of household appliances, garden equipment and lawn mowers.