Plumbing With PEX Tubing
PEX tubing is an easy-to-install alternative to copper pipe. Long used in radiant heating systems, flexible PEX tubing is perfect for water supply lines because it’s easy to run through walls and floors and simple to work with.
The Advantages of PEX
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.
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 and water damage. 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.
Make Crimped Joints at PEX Water Line Fittings
Cut the PEX off perfectly square for leakproof joints. PEX cutters like this Plastic Pipe and Tubing Cutter are available at home centers and online.
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.
Fittings for a Shower Valve
PEX Shutoff Valves
Repair or Replace Kinks
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. 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.
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.
Transitions to Other Types of Pipe
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 (left) to transition from copper, CPVC or steel. Solder, glue or thread on the transition fitting, then crimp PEX line on the barbed fitting. For more information on pipe transitions, see How to Join Dissimilar Pipes.
Run the Line Without Joints
You can run PEX line as you would in a conventional plumbing system, with 3/4-in. main lines and 1/2-in. branch lines. You can also use a “manifold” system, where you run a 1/2-in. line to each fixture from a central spot.
Run your main lines first. 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. Have a helper feed the line to avoid kinks and snarls. Some manufacturers recommend adding abrasion clips at each hole. You must use them 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, leaving a 1-in. gap for the barbed tee.
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. 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.
Upsize to Avoid Poor Pressure
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
Warm up Cold Pipes
Our plumbing expert, Les, knows a plumber who did a job in northern Wisconsin in the middle of winter. The building had no heat, and all the pipes and fittings were freezing cold. When the furnace was fired up and the water turned on, they sprang dozens of leaks. 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.
Plan for Stub-Outs in Advance
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. 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.
Whichever method you use, be sure to add a couple of extra fasteners next to the stub-out to increase stability.
Install PEX Directly to the Fixtures
Many plumbers prefer to run PEX directly to the fixtures so they don’t have to bury fittings behind the walls. It’s hard to keep PEX perfectly straight when PEX exits the wall, so another option is to use a 90-degree copper stub-out when you run a line to a toilet or other fixture where your shutoff valve will be visible.
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.
Keep PEX Away From Hot Stuff
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.