How to install PEX

PEX tubing promises faster installations with fewer fittings and simple connections. Here a professional plumber installs a compression fitting to a manifold that branches the main supply off to other areas of the home.

PEX (cross-linked polyethylene) pipe or tubing is easier to work with, faster to install, and more durable under extreme temperature and chemical exposure than rigid copper, PVC and CPVC pipe.

PEX is also cheaper to purchase and install than copper, and while it costs about the same as PVC and CPVC, its flexible nature makes it easier to fish through walls and eliminates the need for many fittings that are required with other systems. Time saved on jobs often makes this the most economical choice for consumers and the most profitable for professionals.

PEX comes in three grades: PEX-A, PEX-B, and PEX-C, with type A being the most flexible and slightly more expensive. Most professionals find all three types equally easy to work with except for unique or demanding applications, such as a lot of tight corners or working in cold conditions.

While not specified by code, most pros install blue PEX for cold water and red PEX for hot water, making it easier to organize different branches and simplifying subsequent repairs/renovations.

Basic tools

Special tools are not absolutely necessary for some PEX installations, as you can use stab-in or compression fittings to make connections.

These fittings are often too expensive to be practical on large projects, so most professionals make the minimal investment and purchase tubing cutters, which are a necessity; ring crimpers or tubing expanders (depending on the type of fittings you use and the manner in which they are connected); a “go/no-go” gauge to test the integrity of compressed fittings; and a crimp ring removal tool to remove fittings and make adjustments as needed. The total cost for a complete set of PEX tools is typically $200 or less.

PEX eliminates the need for flames, glues or solvents except when connecting it to existing copper or PVC. There are some stab-in fittings available that don’t require solder or glue, but these are sometimes not allowed by some building codes.

Connecting PEX to copper or PVC is simple – just insert a fitting. Some fittings may require solder, glue or compression to join to existing copper or PVC, but the fitting shown here is known as a stab-in fitting; simply insert the pipe or tubing fully into the fitting and barbs will hold it in place.

How to install PEX

When cutting PEX, it is important to make a straight, burr-free cut. That is why the scissor-like tubing cutters are a necessity. They make quick, accurate, smooth cuts.

When measuring the length of PEX needed, remember not to pull the tubing too tight, as it will shrink and expand with temperature changes – 1 inch every 100 feet of pipe for every 10 degrees of temperature change. This can be remedied on short runs by just including a little slack, but longer runs often require making a loop in the run to absorb movement and keep stress away from the fittings.

Working with PEX requires only a few simple specialty tools – tubing cutters, fitting gauge, and fitting tools such as crimpers or expanders are typically all that’s needed in addition to traditional tools.

Most connections begin by slipping a copper crimp ring onto the tubing where you want to connect. The tubing is then inserted into the fitting, making sure it bottoms out on the fitting shoulder. Then, slide the crimp ring so that it is ⅛- to ¼-inch away from the edge of the tubing/fitting shoulder and crimp with the crimper. The crimper should be at a 90-degree angle to the crimp ring. Fully close the crimper on the ring.

Expansion connections are made by placing an expander ring over the tubing and inserting the lubricated tip of the expander tool into the end of the tubing until it stops. Then operate the tool (close the handles or pull the trigger, depending on tool type) to expand the tubing and ring to form a tight seal. Insert the fitting and repeat for the other end of the tubing.

Test the fitting with a “go/no-go” gauge by sliding it over the fitting. It should slide easily and fit snugly with a bit of space between the top of the gauge and the fitting. If it slides over the fitting completely or won’t slide at all, then the tubing will have to be recut and the fitting made again. Some common causes of improperly crimped fittings are:

• ring crimped over the end of the tubing
• crimp tool not at 90 degrees
• not enough ribs covered on the fitting
• distorted rings from a non-uniform crimp
• tubing not cut squarely.

Connecting PEX tubing to traditional shutoffs and other exposed plumbing elements is simple.

Run the tubing from the fitting to its destination much in the same way you would with copper or PVC pipe. Drill through sill plates and studs, making sure horizontal runs are as level as possible. Place nail plates on studs where the PEX runs through to prevent subsequent puncturing from nails or screws.

Straps and hangers are a must when installing PEX – every 32 inches when installed alongside a joist and every 6 feet when installed on top of a beam. Vertical installations require one support piece at every floor level.

Most corners can be handled by simply bending the tubing to fit the space, but tighter corners may require a bend support, which is an elbow “track” the entire tube snaps into for support, or adding an elbow fitting.

Basic conveniences

Residential PEX plumbing installations often use manifolds to distribute the water throughout the system. These typically come in brass and/or copper multi-outlet fittings or a plastic panel resembling an electrical breaker panel, only with tubing instead of wires. These options are usually installed in a mechanical room near the water main and heater, and a separate PEX line is run to each fixture in the house.

This is called “home-run” plumbing, and it eliminates the need for tees and fittings in each line, thereby saving time for the installer and reducing the opportunities for leaks. Homeowners also enjoy the convenience of being able to shut off each fixture in the home individually if they have a problem or want to make improvements. This method uses more tubing, but it is faster and almost always requires only two fittings: one at the supply and one at the fixture.

—By Rob Fanjoy