PEX Plumbing Pipe: Everything You Need to Know

PEX piping is the biggest revolution since the flush toilet. Learn what it is and everything in between with this PEX plumbing guide.

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PEX pipe
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What is PEX Piping?

PEX piping (shorthand for cross-linked polyethylene) costs less than half the price of copper and installs much faster. And since it’s flexible, PEX makes remodeling jobs easier. PEX has a strong “memory;” it always wants to spring back to its original shape. So working with a coil of PEX is like wrestling with a giant Slinky. For most jobs, you’re better off buying 10-ft. “sticks” instead. You may have to pay a few cents more per foot and install a coupler or two, but you’ll avoid frustration and kinks. Even plumbers who run miles of PEX every year often buy sticks than coils.

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PEX vs Copper Piping
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Which is Better – PEX or Copper?

PEX has several advantages over copper pipes:

  • PEX is cheaper than copper. Half-inch PEX tubing costs about one-third the price of copper. Some of the savings will go towards purchasing a special tool to install the fittings. But if you’re doing a medium-to-large plumbing job, you’ll usually save on PEX over copper.
  • PEX fittings are faster to install than copper. If you use a manifold and ‘home-run’ system, it’s like running a garden hose to each fixture — super fast and easy. But even if you install PEX fittings in a conventional main line and branch system, the connections are quicker to make than soldering copper.
  • A PEX supply won’t corrode like copper. If you live in an area with acidic water, copper can corrode over time. A PEX supply is unaffected by acidic water and is therefore a better choice in these areas.

Watch this video to learn more about the PEX revolution:


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PEX vs CPVC Piping
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What About PEX vs. CPVC?

A PEX supply and CPVC cost about the same. But there are a few reasons why PEX may be a better choice. First, a PEX doesn’t require glue, which means you don’t have to work in well-ventilated spaces or wear a respirator. PEX is less likely than CPVC to burst if it freezes. Also, since PEX is more flexible and available in long lengths, it can work better for ‘fishing’ through walls in remodeling situations.

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PEX Pipe Tools
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Do I Need Special Tools?

Yes. When plumbing with PEX, you can use stab-in or compression fittings to make the connections, but they’re too expensive to be practical on large projects. Connections for most PEX supply jobs require a special tool. There are several PEX supply connection methods, but only two affordable enough to be practical for DIYers: crimp rings and cinch clamps.

Crimp rings are a band of metal, usually copper, that you slip over the fitting and compress with a crimp ring tool. The main drawback is that you’ll need either separate crimping tools for one-half inch and three-quarter inch fittings, or a universal tool with a swappable insert (not shown).

Cinch clamps work more like the traditional band clamps you’re probably familiar with. You slip the cinch clamp tool over the protruding tab and squeeze to tighten the cinch clamp. The same tool works for all sizes of cinch clamps.We like the one-handed version shown in the photo because you can hold the ring in place with one hand while tightening it with the other.

The only other special tool you need is a scissors-like cutter for the tubing.

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PEX Pipe Cutter
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How Do I Splice PEX Fittings Into My Existing Pipe?

There are several methods. The easiest is to cut out a section of plumbing pipe and slip in a stab-in tee (left). SharkBite is one common brand of stab-in fitting. This method doesn’t require soldering, which can be a big time-saver. But check with your plumbing inspector if you’re planning to bury this connection in a wall or ceiling. Some areas don’t allow stab-in fittings to be concealed. Another method is to solder in a tee and a PEX supply adapter. Then slip the PEX supply tubing over the adapter and attach it with your chosen connection method (right). You can also use a stab-in tee to connect PEX fittings supply to CPVC. Read the label to find the compatible fitting.

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Stand-In Fittings
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Do I Have to Use Manifolds with PEX?

No. You can install PEX fittings supply just like you would other pipe, with main lines and branches to each fixture. But you lose a lot of the benefits of PEX with this system since it requires so many fittings. With the home-run system, you install a manifold in the utility room or some area that’s close to the main water line and water heater, and run a separate PEX tube to each fixture as shown above. This system uses more tubing, but is fast and only requires two connections: one at the manifold and another at the fixture end. You can also use a hybrid system where you run three-quarter inch hot and cold lines to a set of fixtures — for example, a bathroom — and install a smaller manifold behind an access panel. Then make short runs of one-half inch PEX water line tubing to each fixture.

Manifolds look intimidating. But they actually simplify plumbing runs and reduce possible leaks by eliminating the need for tees and other fittings between the main supply line and the fixture.

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PEX Clamps
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Does it Meet Code?

There is no unified national plumbing code. Before starting your PEX plumbing job, check with your local inspector for specific local requirements.

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Red, white and blue PEX
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Do I Have to Use Red for Hot and Blue for Cold?

PEX comes in red and blue colors to help you keep track of the hot and cold lines. You can use white PEX for everything if you prefer.

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Man holding PEX piping
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Is PEX Reliable?

PEX has been used for decades in other countries, where there are thousands of homes with 30-year-old, leak-free PEX. Most of the problems with PEX systems, in the United States and elsewhere, were due to sloppy installation or faulty fittings rather than the tubing itself.

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Connecting PEX to water heater
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Can I Connect PEX to My Water Heater?

PEX can’t be directly connected to a water heater. First extend a pipe 18 in. from your water heater and connect the PEX to the pipe.

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Insulated PEX Pipe
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Which Tubing Should I Use for Interior Water Lines?

For water lines there are three PEX supply grades: PEX-A, PEX-B and PEX-C. They’re manufactured differently, PEX-A being slightly more flexible. If you’re ordering online, go ahead and spend a few cents extra for PEX-A. But don’t go running around town looking for it; the difference isn’t that big. The plumbers we spoke to said they were willing to use any of the types in their homes. PEX is also popular for in-floor radiant heating systems, though you need PEX tubing with an oxygen barrier.

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How to Connect PEX Pipes to Fixtures
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How Do I Connect PEX to my Plumbing Fixtures?

There are several methods. If the connection will be visible, like under a wall-hung sink, and you would prefer the look of a copper tube coming out of the wall, use a copper stub-out (left). You can connect a compression-type shutoff valve to the one-half inch copper stub-out and then connect your fixture. In areas that are concealed, like under a kitchen sink or vanity cabinet, you can eliminate a joint by running PEX supply directly to the shutoff valve. Use a drop-ear bend support to hold the tubing in a tight bend (right). There are several types of shutoff valves that connect directly to PEX.

If you’re using a manifold system with valves, you may not need to install a shutoff valve at the fixture. Ask your plumbing inspector. We recommend adding one, though. It doesn’t increase the cost much and is more convenient than running downstairs to shut off the water when a repair is needed.

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How to Expand PEX Pipes
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What About Expansion?

PEX supply expands and contracts more than copper, so don’t stretch it tight. Let it droop a little between fasteners. On long runs, it’s a good idea to install a loop as shown to allow for contraction. Another advantage of the loop is that if you mess up and need a little extra tubing, you can steal it from the loop. Also, since PEX moves as it expands and contracts, make sure to drill oversize holes through studs or joists so it can slide easily. And don’t use metal straps to attach it. Use plastic straps instead.

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PEX Pipe Freezing

Will PEX Break or Split if it Freezes?

Probably not. Manufacturers are reluctant to say so, but reports from the field suggest PEX can withstand freezing. You should still protect the tubing from freezing. But since it can expand and contract, it’s less likely to break than rigid piping.

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How to Take Apart PEX Piping
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What if I Goof? Can I Take it Apart?

Sure. There’s a special tool for cutting off crimp rings, and you can use side cutters to remove cinch clamps. But a rotary tool (Dremel is one brand) fitted with a cutoff blade works great for cutting either type of connector (see photo). After you remove the crimp ring or cinch clamp and pull the PEX supply from the fitting, cut off the end of the tubing to get a fresh section for the new connection. If you damage the fitting with the rotary tool, replace the fitting rather than risk a leak.