How to Add PEX Plumbing to Older Pipes

What You'll Need
PEX pipe (white, red and blue)
PEX fittings
PEX straps
Plumbers tape
Support brackets
PEX stub covers
PEX connection tool (rent)
PEX tubing cutter
Channel lock pliers

PEX plumbing is supremely adaptable to existing piping systems via special fittings for PEX to CPVC, copper or threaded steel pipe. No matter how old the plumbing system is in your home, you may use PEX and enjoy the speed and ease of installation this plumbing system offers.


 Step 1 – Install the PEX Tubing

Whatever your home project first install the PEX tubing from the point you’ll connect to the old piping system to the new location. PEX tubing comes in three colors, red, white and blue. To keep hot and cold water lines separate use red for hot and blue for cold.

PEX is extruded and unlike older piping systems it is sold in coils. This means that couplings are not necessary; PEX tubing is a time saver. Fewer connections also means fewer opportunities for in-the-wall leaks.

Fasten the tubing to the wall, attic or crawl space using PEX straps at intervals that prevents sags or loose pipe. At your new termination point use support brackets and stub covers to protect the tubing when you drywall and paint.

Step 2 – Connect the PEX to Old Plumbing

PEX products by different manufacturers employ different means of connection so consult the DIY or hardware store clerk to learn which fittings you’ll need for the brand of PEX you’ll purchase. Chances are they’ll only sell one brand but to preserve the manufacturer’s warranty you must use their approved fittings and follow their connection instructions. Rent the connection tool.

Choose the correct fitting for the type of plumbing that exists, copper, CPVC or threaded steel pipe. Copper and CPVC fittings will use a compression ends, threaded steel pipe fittings will be threaded to match. Install the PEX to the old plumbing fitting first and then the PEX.

Compression fittings slip over the copper or CPVC. Turn the compression nut until tight. Pull on the fitting to ensure a good fit. Apply plumber’s tape (a white tape used to seal the threads) to the steel pipe threads and then screw treaded fittings onto the threaded steel pipe. Tighten with channel lock pliers.

Next squarely cut the PEX tubing using a tubing cutter. If you employ a hack saw or other means ensure no burrs exist. If a burr gets between the tubing and fitting a water leak will eventually occur.

Install the PEX ring over the tube. For crimp systems place the PEX over the installed PEX to old plumbing fitting, then crimp the PEX ring per the manufacturer’s directions. If using the expansion system insert the tool into the end of the tubing then pump the tool’s handle until the PEX is expanded sufficiently to accommodate the old plumbing system fitting. Put the tubing onto the fitting and wait 15 seconds for the PEX shape memory to close and lock the tubing in place. Pull the connection to ensure a secure fit.

Step 3 – Test the Connections

After the connections are completed but before the walls or work space is closed cap PEX pipe ends then turn the water on to test for leaks.