Tools & Materials
Working With PEX
Working with PEX pipe
There are a lot of reasons why PEX (cross-linked polyethylene) plumbing pipe is so popular. PEX is less expensive than copper. It can be run in long lengths without any fittings, which reduces the chance of leaks. It’s less likely to burst in low temperatures. And the biggest advantage of PEX is that it’s super easy to work with. But just because it’s easy doesn’t mean you can’t screw it up. We asked Les Zell, our resident expert, to share some tips, preferences and techniques to help your next PEX install go as smoothly as possible.
Repair or replace kinks
Kinks happen. You can repair kinks with a heat gun, but some PEX brands tend 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.
Install PEX directly to the fixtures
Les prefers to run PEX directly to the fixtures so he won’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.
Cut PEX tubing straight
There’s no reason to spend a bunch of money on a fancy PEX cutting tool. The one our expert is using costs about $12. Whether you use a $100 cutter or just a utility knife, the most important thing is to cut straight. A pipe that is cut at an angle won’t fit properly against fittings, and that increases the risk of leaks.
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.
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.
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. Les’s tip is to use bungee cords to help keep your coils in check. He leaves the cords on and unrolls just the amount he needs. 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.
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 ($12 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.
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.
Warm up cold pipes
Our 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.
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.
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.