Water Conditioning & Purification Magazine

Plumbing with PEX: A Complete Primer

By Dave Yates 

PVC can be a sticky situation. Today, PEX plumbing for residential and commercial applications is rapidly becoming the standard.

All too often, the fast pace of changes to technology and application techniques challenge and frustrate trade professionals. Have you ever repaired your automobile? Today, the dealership’s the only one with the $10,000 diagnostic device that looks like R2D2. A few years ago, just about anyone could install a home security system. But the level of sophistication today makes that one untouchable, too.  

When it comes to plumbing—whether for new construction or residential/light commercial retrofits—flexible PEX tubing is the fastest growing trend in the industry and refreshingly, it’s frustration-free. With some forethought about what you want to accomplish, you can run hot and cold water lines that snake with ease through small holes, between walls and around obstacles with no solder or open flames required, and no need for sticky solvents with long dry-times. This versatile and ultra-durable tubing puts the right technology into the hands of professionals. It’s a change for the better.

A molecular difference
PEX is cross-linked polyethylene tubing. It’s hardy stuff that can last more than a lifetime. The sophisticated cross-linking of the molecules is achieved by either chemical injection or electron bombardment during the manufacturing process, which gives the tubing enhanced strength. PEX-Al-PEX tubing goes one step further and adds a thin layer of aluminum sandwiched between two layers of PEX, which helps the coiled tubing hold its shape after installation. However, it’s also more difficult to work with because of the added rigidity.

Initially, PEX tubing was used chiefly for hydronic (hot water) heating systems in Europe. In the early 70s, WaterPEX was developed for use with potable water. Since that time, it has gained popularity and earned a reputation for reliability. PEX is available in a variety of colors in sizes ranging from 1/4” through 2”, in coils or rigid lengths. When manufactured for use in potable water systems, PEX must meet or exceed ANSI/NSF standard 61. All PEX designed for use with potable water must be marked “Potable” and bear the certification mark of the testing agency. And in Canada, PEX used for potable applications must be tested and certified to the Canadian Standard Association Standard B137.5.

Significant advantages
PEX tubing has grown increasingly popular because it often reduces labor costs, requiring less skill than systems using metal piping. Unlike plastic piping systems that use solvent cements to bond the fittings to piping, PEX systems employ a variety of crimp and compression joints that require no waiting period before applying full pressure.  

PEX has additional advantages as well: resistance against corrosion, tolerance to aggressive water, quiet flow, near elimination of “water hammer” noise, no solvents, glues, flux or soldering required, added freeze protection, long warranties, resistance to scale deposits or growth, ultra durability, fewer joints (lengths can “snake” for hundreds of feet), tubing is non-toxic, it is rated for direct burial in earth or concrete, it’s lightweight, relatively easy to repair kinks, balanced pressure and flow can be achieved when sized and installed properly.

Notable deficiences
PEX tubing has a few drawbacks, however. Ultraviolet rays from sunlight will degrade the tubing and it must not be stored or installed in areas subject to routine exposure. PEX expands at much greater rates than metallic piping systems do, so long hot water distribution runs can take on a life of their own! If PEX tubing isn’t given somewhere to grow when undergoing temperature changes, especially rapid ones, expansion noises can occur. You’ll need to purchase the tool utilized for assuring leak-free crimp ring, barbed or flared joints unless one can be borrowed or rented where you purchase the tubing.
Installation basics

There are two basic styles of PEX tubing installations: “homerun” and “flow-through.” In a homerun system, every fixture or faucet receives its own cold and/or hot water line, run to a central manifold. In most cases, that central manifold will include individual valves to cut off flow if service is required, a tremendous convenience for those middle-of-the-night or holiday emergencies.

The manifold’s hot and cold water inlets are larger in diameter than the fixture outlets, typically 3/4”, for helping balance the flow between fixtures. It is desirable to install the manifolds as close as practical to the incoming water service line and the water heater to ensure maximum flow rates. From the manifold outlets, sizing is based upon the individual fixture flow rates and that’s where some practical plumbing knowledge is required. For residential use, these water lines are often 3/8” or 1/2.” Length of tubing run between manifold and fixture, along with changes in elevation, will affect delivery pressures and gallon-per-minute flow rates. If the manifold must be remotely mounted (see photo), a hot water recirculating line can be added to ensure almost instantaneous hot water delivery at the fixtures.

A flow-through system is piped in the more traditional method using fittings cut into the main line as it runs past fixture branches. In flow-through systems, delivery pressures and flow rates can be adversely affected when fixtures are used simultaneously. Without careful attention to sizing and flow calculations, poor performance and scalding can become real issues.

A combined use of both manifold and flow-through systems offers the best economy. What you’ll want to do is consider which fixtures don’t require steady-state flow rates. For instance, laundry tub and washing machine connections can share a flow-through connection without adversely affecting either fixture. The same is true for a bathroom water closet and vanity, especially if these are closer to the source of hot water (limiting the wait for hot water while cold water in the pipe is pushed out). However, any bathing or shower module should be installed using the homerun method, greatly reducing the potential for scalding caused by sudden pressure imbalance when other fixtures are used.

WaterPEX applications
Hot water lines can be plumbed with red PEX for hot lines and blue PEX for cold water lines. Or, if color-coded piping is not needed, white WaterPEX can be installed—this would be more like having the whole installation piped in copper. Either brass or plastic fittings can be installed. Brass fittings are more traditional, however poly-alloy fittings usually cost less and are more chemically-resistant to some aggressive waters.  Also, poly-alloy fittings would be the best choice if the fitting needs to be buried.  

The WaterPEX CrimpRing system is easy to learn. The copper crimp ring is simply compressed around the tubing and fitting to make a tight fit. The finished connection can be rotated to make piping line up neatly without causing leaks. Connections can be made with wet water lines, impossible with copper sweat connections and difficult with some flare fittings.

The CrimpAll Tool Kit allows you to crimp 3/8”, 1/2”, and 3/4” sizes all in one kit and it costs just about as much as one single-fitting tool. Since most systems need at least two sizes of pipe (1/2” and 3/4”), this is a real value.    

Ease and flexibility
PEX is relatively flexible and allows for a lot of pushing and pulling. Should you accidentally kink the piping, gently warm the tubing with a heat gun until it softens and allows the kink to become smooth. A little bending back and forth, opposite to the kink, slowly allows the pipe to return to its original shape. Impressively simple to do, what actually happens is that the heat “reminds” the long strands of cross-linked molecules where they belong. Their “molecular memory” tells them that they need to resume their original shape. Since heat makes the plastic medium more fluid, the molecules rush to assume the position they had before being kinked. Allow the pipe to cool—visible as it regains the color of the unheated pipe around it—and the healing process is complete.

This simplicity of repair is not shared by PEX-Al-PEX, however, because of the internal aluminum layer. Once kinked, you’ll need to cut out the affected section and install a repair coupling. Crimp ring joints are sealed by use of a crimping tool to squeeze the copper rings around the barbed fitting and apply just the right amount of pressure on the PEX tubing. A “Go—No Go” tool indicates the correct tolerances (see photos).

When running PEX through wooden or metal studs, floor joists and plywood decking, oversize the hole drilled to ensure ease of movement without contacting sharp edges. Use the smooth plastic sleeves for minimizing wear or contact with sharp edges (especially important when running through metal studs). Steel plates should be placed over studs through which tubing passes to protect from puncture by drywall nails/screws and future picture hanging (see photos). If you can’t readily locate nailer plates, blank metal covers from standard two-inch by four-inch electrical boxes work very well and offer adequate resistance to screw or nail penetration.

A tubing uncoiler is a must if you’re going at this solo. Unless, of course, you enjoy frustration, untangling knots or have no fear of a tangled mass that resembles steroidal spaghetti. If you can’t borrow one and aren’t planning on a career in plumbing, one can be built using several scrap pieces of plywood or an electrical cable reel if it’s placed over a stationary pole and you’ve added casters to the reel so it can turn easily.

Although you can cut PEX tubing with a sharp pocket or carpet knife, it’s best to purchase an inexpensive cutting tool to ensure straight cuts with square shoulders. Remember that PEX has a memory and will snap back when cut, which can leave you or your assistant with a black eye! With all of the drilling and overhead work you’ll be doing, don’t forget to wear those safety glasses.

Keep PEX out of exterior walls, as you would any potable water line, when installing in areas that see winter freezing temperatures. Although PEX is more tolerant of freezing conditions than metal piping systems are, it too can crack or break if frozen while filled with liquid and stress is applied. Although, again, it’s fast and easy to fix and you can do it when the pipes are still wet. If you simply can’t avoid running in an exterior wall, make sure the insulation is tight between studs (no air gaps) and that the tubing is placed on the interior side of the insulation.  

Work smart, plumb safe.   

About the author

Dave Yates is a Master Plumber who owns and operates F. W. Behler, Inc., a plumbing, heating and air conditioning firm established in 1900, which is located in York, PA. He can be reached by phone at 717-843-4920 or by email: behler@blazenet.net or www.fwbehler.com

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