PEX Installation & Tools

PEX is cross-linked polyethylene tubing, and it is the most common water supply material in new houses today. It is flexible, quick to install, and handles freezing better than rigid pipe. It also has rules. Each fitting system needs its own tools. PEX has to be kept away from sunlight, supported correctly, and given room to expand. Most PEX problems trace back to mixing systems, skipping a gauge, or treating tube like it cannot be damaged.

What You Will Be Able to Do

• Explain the difference between PEX-A, PEX-B, and PEX-C
• Match tube, fittings, and tools into one correct system
• Make crimp, clamp, and expansion joints and check them
• Route and support PEX, including at bends
• Choose between a manifold and a trunk-and-branch layout

Types of PEX

The letter describes how the plastic was made, not a quality rank. All three types are made to the same tube standards when they are listed for potable water.

PEX-A's shape memory is what makes expansion fittings work. You stretch the tube, slide it over the fitting, and it shrinks back to grip. A kink in PEX-A can often be heated with a heat gun and restored, if the manufacturer allows it. A kink in PEX-B or PEX-C should be cut out.

Some PEX-A tube is also listed for crimp or clamp fittings. Some manufacturers only warranty their own tube with their own fittings, so you need to read what the tube and fittings are actually listed for.

Tube is commonly color-coded red for hot and blue for cold. The color does not change the tube. It just makes the job easier to read later.

Ratings

Listed tube is printed with its pressure and temperature ratings. A common set for water tube is 160 psi at 73 F, 100 psi at 180 F, and 80 psi at 200 F. Normal home water service sits well within those limits. Read the print line on the tube you have, because it tells you the type, standard, and ratings.

Fitting Systems

Fittings, rings, and tools must match. You cannot make one good joint out of parts from two systems.

Making a Crimp Joint

1. Cut the tube square with a PEX cutter. A slanted cut leaves too little tube under the ring.
2. Slide the copper ring onto the tube.
3. Push the fitting in until the tube bottoms against the shoulder.
4. Set the ring about 1/8 to 1/4 inch from the tube end, or as the manufacturer directs.
5. Hold the crimp tool square to the ring and close it completely.
6. Check the crimp with the go/no-go gauge. The "go" slot must slide over the ring. The "no-go" slot must not.

A loose crimp leaks. An over-crimped ring can damage the fitting. Either one means the tool may need adjustment, so check it with the gauge and recalibrate if needed. Cut off a bad joint, or remove the ring with a ring cutter, and start over.

Making a Clamp Joint

Slide the stainless ring on, insert the fitting, and position the ring as directed. Close the tool on the tab until it releases. One tool often handles several sizes, and it works well in tight spots. Do not mix a clamp tool with copper rings.

Making an Expansion Joint

1. Cut the tube square.
2. Slide the expansion ring onto the tube, up to the end or as directed.
3. Expand the tube and ring with the tool. Rotate the tool head as directed so the stretch is even.
4. Immediately slide the tube fully onto the fitting. It should bottom out.
5. Hold it for a few seconds while the tube begins to shrink down.

Cold slows down shrink-back. In cold weather, the fitting may take much longer to grip. Let joints set before pressure testing, and follow the manufacturer's times.

Push-Fit in PEX

Push-fit fittings work on PEX with a clean square cut and a depth mark. Some need a stiffener in the tube, and most include one. Whether they can go inside walls depends on your jurisdiction. Check with your authority having jurisdiction (AHJ) first.

Tools You Will Use

• PEX cutter: Makes a clean, square cut. A dull blade tears tube.
• Crimp, clamp, or expansion tool: Must match the system.
• Go/no-go gauge: Check every crimp. Inspectors may ask to see it.
• Ring cutter: Removes a bad ring without damaging the fitting.
• Bend supports: Hold tube in a tight, stable curve.
• Stub-outs or drop-ear elbows: Give a solid connection at a fixture wall.

Routing PEX

Bending

PEX bends around corners without fittings. That removes joints, which removes leak points. Do not bend it too tightly. The minimum cold bend radius is commonly 6 times the tube's outside diameter, unless the manufacturer allows something else. Nominal 1/2-inch PEX has an outside diameter of 5/8 inch, so 6 x 5/8 gives about 3-3/4 inches. Where you need a tighter turn, use a bend support, which holds the bend at the radius the manufacturer specifies.

Supporting

Support horizontal PEX about every 32 inches, and at changes in direction. Vertical runs commonly get support at each floor, and mid-story guides as your code requires. Use clips and hangers made for PEX. Do not use anything that pinches or cuts into the tube.

PEX grows and shrinks with temperature, much more than copper does. Leave a little slack in long runs instead of pulling tube tight between supports. A tube pulled tight can strain fittings when it cools.

Protecting

• Sunlight: UV light breaks down and embrittles PEX. Store tube out of the sun, keep it in its box, and never leave it exposed outdoors. Your manufacturer limits how long tube can sit in light during construction.
• Heat: Keep PEX away from recessed lights, flue pipes, and water heater vents. Many manufacturers require a metal adapter and a length of pipe, often 18 inches, between a tank heater and the tube. Follow the instructions for the heater and tube.
• Sharp edges: Use sleeves through metal studs and masonry, and a nail plate where tube runs close to the face of a stud. A screw through the tube will be found only after the wall is painted.
• Freezing: PEX can tolerate some freezing better than copper, but it is not freeze-proof, and the fittings can still crack. Insulate in cold spaces.
• Chemicals: Keep PEX away from petroleum products, spray foams, and other materials the tube's manufacturer does not approve. Do not use solder flux near it or torch near it.

Layouts

Manifolds put shutoffs for each fixture in one spot and keep hidden joints out of walls. Each fixture gets its own run, so one shower does not drop when a faucet opens elsewhere.

Worked example. A bathroom has a shower, a lavatory, and a toilet. A home-run layout gives you 2 hot lines and 3 cold lines from the manifold, with one shutoff each. That is 5 lines but no joints in the walls until each stub-out. A branch layout might use 2 lines into the room and 3 tees. It uses less tube, but it has hidden joints that a home-run avoids.

Testing

Pressure test before you cover anything, using the pressure and time your inspector requires. Air or water may be allowed, depending on the code and the tube's manufacturer. Walk the entire run and check each joint. For cold weather, plan for the time expansion joints need.

Common Mistakes

Check Your Understanding

1. A crimp slides into the "go" slot and also into the "no-go" slot of your gauge. What does that mean?

The ring is over-crimped, or the tool is out of adjustment. Remove the ring, check the tool, and crimp again. A good crimp fits the "go" slot only.

2. You have to make a 90-degree turn in a 1/2-inch PEX line and the space only allows a 2-inch radius. What do you use?

A bend support or a fitting. A free bend that tight will kink the tube. The minimum free cold bend is about 3-3/4 inches for 1/2-inch tube unless the manufacturer allows less.

3. A homeowner wants to be able to shut off any fixture in the house from one closet. Which layout fits?

A manifold, or home-run layout. Each fixture has its own line and shutoff.

4. It is 30 F outside and you just made several expansion joints on a new house. What should you be careful about?

Cold slows the tube's shrink-back. Give joints more time before you test, and follow the manufacturer's cold weather guidance.

Key Takeaways

• Tube, fittings, and tools must be one matched system.
• Gauge every crimp, every time.
• Keep PEX out of the sun and away from heat and sharp edges.
• Bending saves fittings, but stay within the minimum radius or use a bend support.
• Support about every 32 inches and leave slack for expansion.
• Manifolds cost more tube but give individual shutoffs and fewer hidden joints.