PEX, a flexible tubing that comes in long rolls or sticks, offers many 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, eliminating most elbows and joints. Second, PEX doesn't sweat under high humidity conditions, and it's 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). Finally, it's super easy to work with, and it's less expensive than copper.
Check with a local plumbing inspector for local requirements and read the manufacturer's directions, which may vary slightly from what we show here.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.
Use the Same Stuff
There are several different manufacturers of PEX. It is very important that you know which brand of pipes you’re working with and install only that manufacturer’s connectors and fittings. If you mix and match materials, you will void your warranty and may fail your inspection. Worst-case scenario: You’ll end up with leaky pipes, water damage and extremely unhappy homeowners. Not all products have recognizable markings on them, so leave a few of the packaging labels on-site to appease the inspector and for future reference.
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 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.
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.
PEX is plastic, and plastic melts. So keep your PEX pipes away from hot stuff. Codes commonly require PEX to be at least 18 in. away from the water heater and 6 in. away from single-wall flues on gas water heaters. And stay well clear of furnace flues, wood-burning stove pipes and any other item that gets hot.
Since PEX won't burst when it freezes, you might be tempted to use it for seasonal dwellings, such as cabins. PEX is soft, however, and rodents could chew through exposed lines.
Kinks happen. You can repair kinks with a heat gun, but PEX tends to rekink in the previously kinked spot, especially if the pipe needs to make a bend at the kinked location. It’s best to cut kinks out and use the shorter sections of pipe elsewhere. If you get a minor kink in the middle of a long, straight run and you don’t want to cut it out, heat the pipe with a heat gun and then cover the damaged area with a hanger or abrasion clip (see “Protect Your PEX,” below). That will help the pipe keep its shape.
Protect Your Pex
PEX expands and contracts with changes in temperature, which causes the pipes to move back and forth. Several years of even the slightest movement can wear a hole in PEX pipes, especially if they're rubbing against something abrasive.
If your pipe is in contact with a joist, duct, electrical box or steel stud, or it is passing through a block wall or concrete slab, it needs to be protected. You can protect your pipe with abrasion clips, cover the pipe with inexpensive pipe insulation, or enclose it with a larger pipe. Pipes that are encased in concrete (for in-floor heating, for example) are OK because the concrete holds them in place. And pipes running straight through wood studs and joists are fine too—just protect the pipe in areas where it bends as it passes through.
If you're adding a guest bath or finally getting to that laundry tub you've been promising for the past five years, you'll have to join PEX to the existing system. Make sure you shut off the main water supply, then drain the lines. Use the special transition fittings shown to transition from copper, CPVC or steel. Solder, glue or thread on the transition fitting, then crimp PEX line on the barbed fitting. Note: Plumbing codes vary on allowing brass/steel connections. If they're allowed, be sure to apply liberal amounts of both Teflon tape and pipe joint compound to prevent reaction between the two metals.
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” 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.
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).
Home Runs Are Best
You can install PEX with main lines and branches to each fixture, but “home runs” are better. A home run is one line that runs directly to a fixture, starting at a manifold (above). Home runs require more piping but deliver a stronger and more consistent water flow. Also, installing home runs is fast and requires only two connections (one at the manifold and another at the fixture end), which reduces leaks.
You can also use a hybrid system where you run 3/4-in. hot and cold lines to a set of fixtures—for example, in a bathroom—and install a smaller manifold behind an access panel. Then make short runs of 1/2-in. lines to each fixture. Another cool thing about home runs is that each fitting has its own shutoff at the manifold. That means you can shut off just that fitting to do some work—you don’t have to shut off the water to the whole house.
The inside diameter of 1/2-in. PEX is smaller than that of 1/2-in. copper (and even smaller with fittings). If you're tearing out copper and replacing it with the same size PEX pipe, the water flow to the fixtures may be noticeably lower when you're done. If you're working on a house that has less than 45 lbs. of pressure or a flow rate of less than 4 gallons per minute, make sure you install home runs, and consider going up in size to 3/4-in. pipe. A simple way to test water pressure is to hook up a hose bib pressure gauge (sold at home centers) to your spigot. To check your flow rate, just see how many gallons of water flow into a 5-gallon bucket in one minute.
Control Your Coil With an Elastic Cord
One complaint about working with PEX is that the coils have a mind of their own. As soon as the banding is removed from the coils, they tend to explode out in every direction. To deal with this, use bungee cords to help keep your coils in check. Leave the cords on and unroll just the amount you need. If your coil comes wrapped in plastic, don’t remove it. Sometimes you can just feed out pipe from the innermost section of the coil. If you have just a few smaller runs or short lengths to install, buy sections of straight pipe—it's a lot easier to work with.
FYI: If you're installing PEX in the winter in a building with no heat, and all the pipes and fittings are freezing cold, expect lots of leaks when the furnace is fired up and the water turned on. Most PEX manufacturers recommend you work with pipe at temperatures above freezing. The whole length of the pipe doesn’t need to be warm, just wherever you make a connection. You can heat those cold pipes and fittings with a heat gun or hair dryer, leave them in a warm vehicle for a while or keep fittings in your pocket. Heck, you can even warm a pipe in a thermos of hot water.
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 with an elbow (Photo 12). You can also run PEX directly to the fixtures (see photo).
Whichever method you use, be sure to add a couple of extra fasteners next to the stub-out to increase stability.
Avoid Kinks at Tight Corners
PEX's flexibility makes it easy to work with. It can be bent around pretty sharp corners without the need for an elbow fitting. But if you try to bend it too much, you’ll end up kinking it. Installing a bend support will prevent this, and it will also protect the pipe from abrasion.