Plumbing with PEX Tubing

Overview

Step into just about any house built in the past 50 years, and odds are, you're going to see one of three materials used for the water supply lines: copper, steel or CPVC. While these three materials are reliable and fairly easy to work with, a flexible tubing called PEX (“cross-linked” polyethylene) has become popular with many plumbers. PEX has been used for many years for in-floor heating systems but only more recently for supply lines. You may find it in a newer home, and, since it's easy to work with, you might consider it as an alternative to traditional materials when running new water lines. It's now available at many home centers. In this article, we'll introduce you to PEX and show you the basic techniques for working with it.

The advantages of PEX

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Photo 1: PEX tubing

PEX is a somewhat flexible plastic pipe that you can run for water supply lines much like copper or CPVC.

PEX, a flexible tubing that comes in long rolls, offers several advantages over traditional piping. First, you can usually make long continuous runs, eliminating most elbows and joints. You can snake long runs through joists and studs. Second, PEX doesn't sweat under high humidity conditions, and it's also resistant to bursting, even if the lines freeze solid. Third, joints are easier. You add fittings simply by crimping metal rings over barbed fittings using a special crimping tool. Crimping takes seconds and is virtually error-free, avoiding the hassle of soldering (copper) and the fumes and mess of cementing (CPVC).

However, PEX has a couple of drawbacks. First, the crimper is expensive. You can sometimes rent one, but each manufacturer wants you to use its proprietary crimping tool for its tubing. The rental store might not carry the right one. A second drawback is a somewhat sloppy appearance. And third, the fittings are more expensive than for copper and CPVC systems. The overall cost of materials is about the same as for other systems.

Some home centers may stock more than one brand of PEX. Buy the same brand of pipe, fittings and tools to ensure proper installation and fulfill warranty conditions.

Check with a local plumbing inspector for local requirements and read the manufacturer's directions, which may vary slightly from what we show here.

Make crimped joints at fittings

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Photo 2: Crimping tool

Make connections with special crimp fittings in which you clamp a copper ring around an inner fitting sleeve.

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Photo 3: PEX cutter

Cut the PEX off perfectly square with a special PEX cutter for leakproof joints.

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Photo 4: Stab-in fittings

Use stab-in fittings only where you have access to the joint. These fittings don't require a special tool. You simply push the pipe into the openings. Press the outer ring onto the fitting to release the pipe.

The heart and soul of the PEX system is the barbed fitting/crimping ring combination (Photo 2). There's no need for solder, glue or pipe wrenches—just position the crimping ring over the end of the PEX pipe, slide the pipe over the barbed fitting and use the special crimping tool to compress the ring. Just be sure to center the ring over the barb and depress the crimping tool's handles completely.

That's it. The resulting seal is watertight. The crimping tool shown can be used for both 3/4-in. and 1/2-in. crimps, important when you're running several sizes of pipe. If you make a mistake in crimping, you can use a special decrimping tool to remove the ring and then reuse the fitting. A clean, square cut is essential for a proper seal; the PEX cutter shown in Photo 3 works great and is available anywhere PEX is sold.

Another type of fitting for joints, called “stab-in” fittings (Photo 4), is also sometimes available. You simply push the ends of the PEX into the fitting, where it locks in place. These fittings are available for most situations, including joining PEX to copper and to CPVC. However, we don't recommend them unless you have easy future access to the joint.

Fittings for a shower valve

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Photo 5: Threaded PEX fittings

Use threaded fittings for shower valves. Tighten the fittings before crimping the PEX. A plastic bracket forms the sharpest 90-degree angle permitted for this brand of PEX.

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Photo 6: PEX shutoff valves

Crimp PEX shutoff valves into the hot and cold lines.

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Photo 7: Drop-ear elbow

Use drop-ear fittings designed for PEX for the shower arm and tub spout.

Most shower valves have threaded ports for the supply lines. Tighten the threaded fittings into the shower valve before crimping on the PEX line. Then run the lines through the studs (Photo 5), make 90-degree turns with a plastic or metal elbow sleeve, or crimp in right-angle fittings in tight quarters (Photo 12). Splice in shutoff valves as well (Photo 6). Then, install “drop-ear elbows” to stabilize the spouts and/or showerhead assemblies, just as you normally would (Photo 7). Once you've secured your drop-ear elbows and threaded fittings, run the PEX line between the valve and the drop-ear elbows and crimp each joint.

Transitions to other types of pipe

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Photo 8: PEX transition fittings

Different types of water pipe require different PEX transition fittings.

Run the line without joints

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Photo 9: PEX eliminates joints

Snake a single length of PEX through joists and between floors. It doesn't require joints unless you have tight turns. Have a helper feed it to avoid kinks in the plastic.

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Photo 10: Support long runs

Support PEX every 24 in. and at turns with special clamps.

You can run PEX line a couple of different ways. Most often, you run PEX as you would in a conventional plumbing system, with 3/4-in. main lines and 1/2-in. branch lines (Photo 1). You can also use a “manifold” system, where you run a 1/2-in. line to each fixture from a central spot. But we won't show that system here.

Run your main lines first—don't worry about cutting in your branch lines yet. If you're running PEX through joists or studs, drill 3/4-in. holes for 1/2-in. piping and 1-in. holes for 3/4-in. piping. You don't have to drill holes in an exact straight line; there's enough flex in the pipe to feed it through misaligned holes. Have a helper feed the line to avoid kinks and snarls (Photo 9). Where the pipe runs along a surface, be sure to support it every 16 to 24 in. to reduce sag and give the piping a neat appearance (Photo 10). Some manufacturers recommend adding “suspension clips” (not shown) at each hole to prevent abrasion. You must use suspension clips for PEX that goes through metal studs, and nail protection plates when the tubing runs within 1-1/2 in. of the face of a stud or joist.

Once you've run your main line, go back and mark the location of each branch line with a marker, leaving a 1-in. gap for the barbed tee. Cut the 1-in. gap out of the main line, crimp your tees into place and run your branch lines to the appropriate fixtures. This eliminates the need to measure each section of main line and makes installation both faster and easier.

You can generally flex PEX into gradual bends without risking a kink (Photo 10). When you need to turn a corner, many times you can bend the pipe manually and eliminate the need for an elbow. But different brands of PEX have different “kinking” points, so always read the manufacturer's guidelines. Buy special plastic or metal elbows (Photo 5) to make the tightest recommended turns virtually kink-proof.

If you need to make a really sharp turn, cut the line and use a copper 90-degree ell (Photo 12).

Plan for stub-outs in advance

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Photo 11: Attach PEX to stub-outs

Use special copper stub-outs for more visible locations. Cut off the tube and mount a standard shutoff valve.

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Photo 12: Use angle fittings for tight turns

Make tight turns with 90-degree angle fittings. For hidden stub-outs, use shutoff valves designed for PEX.

There are a couple of options for bringing PEX out through a wall (stub-outs). If the piping is going to be exposed, say for a pedestal sink or a toilet, buy a copper stub-out and crimp it onto the PEX (Photo 11). Then use standard shutoff valves. If the stub-out will be hidden, inside a cabinet, for example, or you don't mind the look of exposed PEX line, use a barbed PEX shutoff valve (Photo 12).

Whichever method you use, be sure to add a couple of extra fasteners next to the stub-out to increase stability.