How To Install PEX

by Alden Smith

To the uninitiated, PEX is cross-linked polyethylene.  Though often used in radiant heat installations, it is now being used quite a bit in hot and cold plumbing applications.  Unlike rigid copper, it is easy to work with and is approved by almost all local building codes.  The tubing is such a new advancement that allegedly it hasn't even made it into the books at some local associations.  This article will focus on PEX, its applications, and how it is installed.

What Is PEX?

Through the manufacturing process, links between polyethylene molecules are formed to create bridges, thus giving it the name "crossed linked".  This tubing is especially good in hot water applications.  Because of its design, PEX is more durable under temperature extremes and chemical attack, and is more resistant to creep deformation.  PEX was developed in the 1960s, and was used mainly in Europe until the 1980s.

Installing PEX

There are many different applications for PEX installations; here we will focus on the installation for a hot and cold water distribution system.

Tools needed:

• Fittings
• PEX tubing designed for the job
• Tubing cutter
• Ring crimper
• crimp rings
• "Go/No-Go" gauge
• Crimp ring removal tool
  

When cutting PEX, it is imperative that it is a straight, burr free cut.  Measure out the length of PEX you will need for installation and cut it with the PEX tubing cutter.  These pliers are especially designed for PEX and should always be used.

When you have the PEX cut to length, slip a copper crimp ring onto the pipe.

Insert the tubing into the piper fitting.  It should bottom out on the shoulder of the fitting. Slide the copper crimp ring up so that it is 1/8" to 1/4" away from the tubing.

Crimp the copper crimp ring with the ring crimper, insuring that the crimper is at a 90 degrees angle from the crimp ring.  Close the crimp tool fully on the crimp ring.

Now, test the crimp with the Go/No-Go gauge. The Go-gauge should slide onto the fitting with ease.  It may be tight where the crimping tool has marked the crimping surface during the crimping operation.  The No-Go gauge must not slide over the fitting.  If it does, the tubing must be recut and the joint made once again.

Inspect Your Work

A bit of finesse is required here.  It is very important that the finished joint is done correctly.  Here is what to look for:

• Ring crimped over the end of the tubing. Not enough ribs covered.
• Crimp tool not at 90 degrees.  Plastic dented and not enough rib coverage.
• Copper crimp ring not completely covered by crimping tool.  Ring is distorted with a non uniform crimp.
• Tubing not squarely cut. Does not cover ribs of fitting.
  

All of these will cause a potential leak hazard and an insufficient connection. The crimp tool is designed to make accurate crimps.  It may need adjustment if you continually make improper connections.

Running The Tubing

PEX will install a bit differently than normal PVC or copper tubing.  Allowances must be made for ever 10 degrees of change in temperature. PEX will contract one inch every 100 feet of pipe with every 10° of temperature change. Offset this by making a loop in the PEX that is no more than 8 times the diameter of the tubing.

You will need straps and hangers when installing the PEX.  It must be supported at least every 32 inches if tubing is installed alongside a joist.  If it is placed atop a beam, it should be supported every 6 feet. When run vertically, it will require support at every floor level. When installing, always leave slack in the tubing to allow for contraction.  The support hangers should not be so tight that they will restrict movement of the PEX.

Some PEX FAQ's

Why is PEX so good for plumbing needs?

PEX is strong, flexible, and can withstand extreme high and low temperatures.  It is easy to install.  PEX is highly resistant to chemicals found in the plumbing environment.

Can PEX be installed outside?

At the present time, no.  Technology is advancing so that in the near future you may see PERX that is usable outdoors.

Can PEX be used under a cement slab?

Yes. PEX comes in long rolls, and can be run under a slab without the use of fittings.

Can PEX be used for underground applications?

PEX is an excellent underground water service piping.

What different joining systems are available?

There are several methods, all involving mechanical fittings.

PEX is relatively new in the American market.  It is good for installation such as radiant heat systems.  Give PEX a try in your next plumbing project.



Alden Smith is an award winning author and regular contributor to DoItYourself.com. He writes on a variety of subjects, and excels in research.