If you specialize in residential applications, you’re most likely familiar with crosslinked polyethylene, or PEX — the flexible, durable, plastic piping system that’s become increasingly popular in new-home construction. But if you’re in the commercial space where PEX is still relatively new, you might not be aware of the product’s variations that can make or break your installation.
A little background first: PEX was invented in 1968, and by the 1970s, it was being used throughout Europe for water distribution systems. PEX was brought to North America in the mid-1980s for use in residential radiant floor heating applications. By the mid-1990s, it was being used for residential potable plumbing as well. During the early 2000s, its use evolved to combine a home’s cold-water plumbing with fire sprinklers for a “multipurpose” system.
Commercial projects began using PEX in the 1990s for radiant heating (and eventually radiant cooling) applications. However, the past 10 years has seen an increase in PEX use for domestic hot water, as well as hydronic heating and chilled-water applications.
Both residential and commercial industries see the same benefits of PEX, namely:
- Its flexibility and long coil lengths, dramatically reducing the need for fittings.
- Its high durability, corrosion resistance and freeze resistance for greater longevity.
- Its cost-effectiveness compared to materials like copper.
What are the most important facts you need to know about PEX? Currently, there are three manufacturing methods, known as PEX-a, PEX-b and PEX-c. These methods generate pipe that possess varying degrees of crosslinking. Crosslinking is important because the higher the degree of crosslinking, the greater the flexibility, durability and other benefits of the pipe.
PEX-a pipe is manufactured using the “Engel” method (named after German inventor Dr. Thomas Engel). This method is commonly referred to as “hot” crosslinking because the polyethylene molecules are linked during the extrusion process when polyethylene is above the melting point.
This method results in the highest degree of crosslinking of all PEX types — around 85 percent. This level of crosslinking offers the greatest flexibility, allowing the tightest bend radius to eliminate fittings with changes in direction. PEX-a also offers a unique thermal and elastic memory. This means kinks in the pipe can be repaired with the use of a heat gun. It is important to know that only PEX-a can be kink-repaired. You cannot do this with other PEX types.
The higher degree of crosslinking of PEX-a also offers greater durability in freeze/thaw cycles, keeping the integrity of the pipe intact.
Finally, PEX-a is the only PEX pipe manufactured specifically to allow for larger ASTM F1960 expansion fittings. While you can use ASTM F1960 expansion fittings with PEX-b or PEX-c pipe, strength tests have shown the strongest connection is between PEX-a pipe and expansion fittings, due to the thermal and elastic memory of the PEX-a pipe.
PEX-b is crosslinked after the extrusion process by placing the pipe in a hot-water bath or steam sauna. The degree of crosslinking for PEX-b is typically around 65 to 70 percent. Because this method is not as evenly crosslinked as PEX-a, it is a stiffer product.
It also does not have the same degree of thermal memory as PEX-a, so you cannot repair kinks with a heat gun. If you get a kink in the pipe, you have to cut it out and install a coupling.
Lab tests have shown that while you can create an expansion connection with PEX-b, it will not hold as securely as a PEX-a connection. The stiffer quality of PEX-b pipe can create tiny cracks in the pipe wall when expanded, compromising the fitting connection.
This pipe type typically works best with insert fittings using a copper crimp or stainless steel clamp ring around the outside of the pipe to hold the fitting in place. While push-to-connect fittings are approved for use with all PEX types, testing has shown these fittings can blow off with higher pressures.
The main drawback with insert fittings is that the crimp or clamp ring is working against the shape memory of the pipe. Remember, PEX always wants to revert back to its original shape. If you have force pressing against that shape (such as a ring crimping or clamping down on it), you’re not working with the pipe; you’re working against it.
Also, insert fittings have a smaller internal diameter (so they can go inside the unexpanded pipe). The smaller internal diameter can restrict flow and reduce system performance.
PEX-c uses an electron beam to change the molecular structure of the pipe after the extrusion process. The PEX-c method requires multiple passes under the beam to reach a degree of crosslinking of 70 to 75 percent.
Side effects of this process are discoloration due to oxidation (from natural white to yellow, unless other pigment is added), and a slightly stiffer product. PEX-c can also accept expansion-style connections, but it will also not hold as securely as a PEX-a connection.
And, just as with PEX-b pipe, you cannot repair kinks.
PEX standards, codes and listings
There are numerous standards, codes and listings for PEX to ensure it is being manufactured and installed properly to meet the needs of an application. The most common standards are the ASTM F876 Standard Specification for Crosslinked Polyethylene (PEX) Tubing that covers the materials, dimensions and performance for the pipe, as well as the ASTM F877 Standard Specification for Crosslinked Polyethylene (PEX) Hot- and Cold-Water Distribution Systems that covers the requirements, test methods, and marking methods for the PEX components.
Various manufacturers have other standards, codes and listings that their pipe meets. Be sure to check the pipe submittal or the manufacturer’s website to obtain a thorough understanding of all the standards, codes and listings for the PEX product you plan to install.
Also know that while PEX is approved in all national and local plumbing and mechanical codes, some jurisdictions still do not allow PEX. Be sure to check with your local jurisdiction before installing the product.
One last piece of advice:
When installing PEX pipe and fittings, it is important to stick with the same manufacturer for all components. Mixing different pipe and fittings from different manufacturers can limit the warranty and add confusion/frustration if there is a need for service. Using one brand of PEX and fittings will ensure a full warranty and greater confidence with service and support.
For more information about PEX, visit the Plastics Pipe Institute website at plasticpipe.org or the Plastic Pipe and Fittings Association website at ppfahome.org.
About the Author
Kim Bliss is the content development manager at Uponor. She can be reached at [email protected].
Utilizing larger-dimension PEX for commercial applications
After walking the 2016 AHR Expo in January in Orlando, Fla., it is clear plumbing and HVAC consulting-specifying engineers, contractors and building owners have more choices than ever when selecting materials and standards for pipe, valves and fittings for domestic-water system applications.
PVF manufacturers from around the globe have been aggressively pursuing the North American market due to the more stabilized economy and optimistic building forecast as compared with the European or Asian markets. However, many of these new products have yet to be proven in the field by withstanding the operating conditions of a commercial domestic-water piping system.
Over the past decade, PEX — an acronym for crosslinked polyethylene — has become the most-installed plumbing pipe for new (and re-piping) residential applications compared with copper and CPVC combined. So it’s no surprise PEX is now expanding into the commercial market as well. With 25 years of successful operation in potable-water systems, PEX has proven itself a major player in the residential marketplace. Meanwhile, the commercial sector is beginning to understand the benefits of this flexible, durable piping product.
PEX piping systems use either insert fittings or expansion fittings to create connections.
- Insert fittings are listed to ASTM F1807 (Standard Specification for Metal Insert Fittings Utilizing a Copper Crimp Ring for SDR9 Cross-linked Polyethylene (PEX) Tubing) and ASTM F2159 (Standard Specification for Plastic Insert Fittings Utilizing a Copper Crimp Ring for SDR9 Cross-linked Polyethylene (PEX) Tubing).
- Expansion fittings are listed to ASTM F1960 (Standard Specification for Cold Expansion Fittings with PEX Reinforcing Rings for Use with Cross-linked Polyethylene (PEX) Tubing).
Until recently, PEX pipe, valves and fittings were limited to 1/2-in. through 2-in. sizes. However, with the continued expansion of larger-dimension product offerings and increased code approvals and listings for use in commercial plumbing and hydronic piping applications, PEX is strengthening its market share. Much like it did in the residential sector, PEX again has the potential to become the dominant player in the world of commercial plumbing and hydronic piping systems.
Today, PEX pipe — specifically ASTM F1960 fittings — is being offered in the larger sizes of 2 1/2 in. and 3 in., allowing greater use and flow in commercial plumbing and hydronic piping applications. This newly expanded PEX pipe and ASTM F1960 fittings offering allows designers and specifiers to select a PEX system, rather than copper, CPVC or other traditional materials used in commercial piping systems.
PEX pipe is manufactured to be a copper tube size (CTS) pipe with a wall thickness conforming to a standard dimension ratio of 9 (SDR9). In addition, the pipe is approved by all model plumbing codes for domestic water-piping applications according to ASTM F876 and F877 standards.
Three types of PEX
PEX-a: The Engel method, also called PEX-a, is named after German inventor Dr. Thomas Engel. This method crosslinks the polyethylene molecules during the extrusion process when polyethylene is in its amorphic state (above the crystalline melting point). This method also is referred to as a “hot” crosslinking process.
With the PEX-a method, crosslinking reaches about 85%, the highest degree of all PEX types. This level of crosslinking creates the greatest flexibility as well as thermal and elastic memory. The latter characteristic means kinks in the pipe can be repaired with the use of a heat gun, and pipe can be expanded to accept a high-flow ASTM F1960 “cold-expansion” fitting.
PEX-b: The Silane method, also called PEX-b, crosslinks the tubing after the extrusion process by placing the pipe in a hot water bath or steam sauna. The degree of crosslinking for PEX-b is typically around 65 to 70%. Because PEX-b is not as evenly crosslinked as PEX-a pipe, it does not have the same degree of flexibility or thermal memory (hence, no kink reparability).
PEX-c: The E-beam method, also called PEX-c, uses an electron beam to change the molecular structure of the tubing (i.e., crosslinks) after the extrusion process. The PEX-c method requires multiple passes under the beam to reach a 70 to 75% degree of crosslinking. Side effects of this process are discoloration due to oxidation (from natural white to yellow, unless other pigment is added), and a slightly stiffer product.
Key characteristics and considerations
PEX hydrostatic temperature and pressure ratings: PEX pipe meets the following temperature and pressure ratings:
- 200° F at 80 psi;
- 180° at 100 psi; and
- 73.4° at 160 psi.
In accordance with ASTM F876, the minimum hydrostatic burst pressure for PEX pipe is 480 psi (for 1/2-in. pipe) and 475 psi (for 3/4-in. pipe and larger) at 73.4°.
Thermal conductivity: PEX pipe does not sweat like copper due to its very low coefficient of thermal conductivity of 0.219 Btu/(hr•ft²•°F). Copper has a coefficient of thermal conductivity between 300 and 400 Btu/(hr•ft²•°F), depending on wall thickness (Type K, L or M).
The thicker walls of PEX pipe act as an insulator, offering insulation values of about R-0.19. The heat transfer from copper is much greater; PEX offers up to 30% better insulating value when comparing uninsulated PEX to uninsulated copper pipe.
Surge pressure and sound intensity: Typical polymers will absorb sound in the range of 10 dB/cm; metals, on the other hand, absorb sound only in the range of 0.1-1.0 dB/cm. For a given change in velocity, the intensity of sound from a copper pipe will be at least eight times higher than that of PEX-a pipe. Furthermore, using PEX instead of copper can reduce peak pressures caused by a quick-acting valve by 18 to 40%.
Freeze resistance: Due to its flexibility and expansion characteristics, PEX pipe is much more freeze-resistant when compared with copper and CPVC. Because of its thermal and shape memory, PEX-a pipe, in particular, can expand up to three times its extruded diameter. Consequently, if water freezes in the pipe, the pipe can flex to accommodate the expansion and then shrink back down after the ice thaws.
Chlorine resistance: All PEX manufacturers are required to test their pipe’s resistance to hot, chlorinated water and list the PEX designation on the pipe’s print stream. Some PEX manufacturers meet the highest requirement for chlorine resistance at end-use conditions 100% of the time at 140°. Consult with individual PEX manufacturers to verify whether their PEX designations meet the intended application.
Suspended piping: PEX can be supported by the same CTS pipe hangers or supports used for metallic pipe. The horizontal support spacing for 1 in. and smaller PEX is 32 in.; for 1 1/4 in. and larger pipe diameters, 48 in. (Note: Some codes allow for only 32-in. horizontal support spacing regardless of pipe size, so be sure to check local codes for verification.)
For suspended applications requiring more or less restrictive support spacing, engineers can specify products offering continuous support, helping to lower labor and material costs. One such product is an extruded, galvanized, half-round CTS channel that snaps onto the PEX pipe, offering greater support spacing of 8 ft., and the ability to field-insulate around the piping and channel.
Risers: PEX risers require a CTS riser clamp at the base of each floor. The installation also should include a riser clamp at the top of every other story to limit the expansion and contraction to pipe lengths less than 25 ft. This translates to an expansion of about 1 1/2 in. in 25 ft. at a 60° Delta T (installed at 60° with an operating temperature of 120°). In this application, the piping will snake slightly in areas where it is not constrained, requiring the use of mid-story guides.
Fire-resistant construction: PEX manufacturers are required to test their products and assemblies to multiple ASTM fire-resistant standards if such products are to be installed in fire-rated applications. Some PEX manufacturers have been approved for installation in applications requiring plenum-rated pipe as well as up to three-hour fire-resistive ratings.
Most firestop manufacturers offer multiple “listed” solutions for through-penetrant applications using PEX pipe. Consult with the PEX manufacturer to verify that its specific fire-resistive construction ratings and listings match the intended application.
Direct burial: PEX pipe is approved for direct burial in soil or concrete, as are certain PEX fittings and fitting materials. Check with the manufacturer for approved applications and installation guidelines. Some manufacturers also offer pre-sleeved pipe for direct-burial applications. This corrugated sleeving provides added protection for installations in concrete slabs or soil. Also, having the PEX inside the sleeve allows for quick and easy removal and replacement of the PEX pipe, if necessary, without having to break up the slab or soil.
As new PVF products are introduced into the North American market, it is reassuring to know proven PEX systems with ASTM F1960 fittings are expanding their offerings, allowing industry professionals the opportunity to select a system type that has demonstrated reliability and performance.
This article was originally titled “Going bigger” in the April 2016 print edition of PM Engineer.
Why should I consider installing a Uponor PEX plumbing system in my home?
If you are currently using old galvanized plumbing in your home, it may be time to replace it. The going option for repiping your home is PEX. But what is PEX, and should you use it in your home?
What is Uponor PEX?
Uponor PEX plumbing systems is a flexible, durable plastic piping product called crosslinked polyethylene (PEX) tubing used to distribute the water throughout your home. PEX tubing is a clean, non-toxic, and extremely durable piping product that will not pit, scale or corrode. And although not a big problem for Houstonians, it even helps resist freeze damage.
There are three different types of PEX tubing: PEX-a, PEX-b, and PEX-c. Uponor manufactures PEX-a tubing is considered the superior type of PEX in the industry because the crosslinking is done during the manufacturing process when polyethylene is in its amorphic state (above the crystalline melting point). Because of this, the degree of crosslinking reaches around 85% (higher than PEX-b or PEX-c), resulting in a more uniform, more flexible product with no weak links in the molecular chain. We Do Repipes is a Uponor Certified Installer and we only use superior PEX-a tubing for all repipes. If you are considering a repipe for your home and have additional questions about using PEX in your Houston area home, call to speak to an expert, 832-819-8337.
According to the manufacturer, Uponor AquaPEX tubing for drinking water is held to the plumbing industry's highest standards.
"In addition to testing and certification at NSF International, Canadian Standards Association (CSA), and Underwriters Laboratories (UL), Uponor PEX tubing has been tested and approved for potable-water applications by the most demanding agencies in the world, including DVWG-Germany, KIWA-Netherlands, CTSB-France, and BSI-Great Britain. Toxicity extraction testing performed in accordance with ANSI/NSF 61 "Drinking Water System Components – Health Effects" verifies Uponor PEX tubing does not leach potentially harmful substances into the drinking water." - https://www.uponor-usa.com
Why Consider Installing PEX Your Home?
A Uponor PEX plumbing system is a clean, healthy, quiet, and reliable system that provides many benefits over a copper or PVC system, including corrosion resistance, better freeze resistance, fewer connections for fewer potential leak points, and a 25-year limited warranty.
We Do Repipes offers 5 Star Repiping Services to Houston Residents and the surrounding areas. Call us today for a free consultation for whole-house- repipe services. Call 832-819-8337 or request a quote online.
Galvanized Pipes, PEXWe Do Repipes Teamrepipe, Uponor PEX, PEX
Uponor PEX tubing is increasing in popularity for commercial domestic water piping installation. PEX is an acronym for cross-linked polyethylene, and is a flexible, durable, and sustainable product. For over 40 years, it has been successfully incorporated into residential and commercial building projects.
Benefits of Uponor PEX Tubing
- Resistant to pitting, scaling, or corrosion
- Expands up to 3x its diameter, providing freeze damage protection
- Cost-effective, efficient installation
- Available in sizes up to 3” for potable and 4” for closed-loop hydronic applications
- EP multi-port tees offer 60% fewer connections
- ASTM E84 plenum listing for Uponor AquaPEX, PEX-a-Pipe Support and ProPEX EP fittings up to 3”
- NSF International certification for water purity
Uponor provides an exclusive pipe sizing calculator on their website: https://www.uponorpro.com/calculator/.
Uponor PEX Domestic Hot-Water & Cold-Water
Uponor AquaPEX® pipe and ProPEX® expansion fittings can be installed overhead, through framing, in the slab or below grade for the following applications:
- Main distribution piping
- Riser distribution piping
- Residential/Hotel unit in wall piping
- In slab
- Under slab
- Public flush banks
- Purified water systems
- Reclaimed (graywater) systems
- DHW recirculation
- Building service supply piping
- District distribution piping
Uponor PEX tubing is an excellent application for hospitals, hotels, and public restrooms. BCH will be using it for the hotel units at the JW Marriott project in downtown Tampa. Beyond commercial plumbing, Uponor is utilized in radiant heating and cooling, pre-insulated piping, and hydronic piping. To learn more about how PEX tubing can enhance your next project, call or email a member of the BCH estimation team.
Pex tubing uponor
Trust forms the basis of any successful partnership. We create trust together with our partners: Customers, prospective customers and suppliers. We establish this with shared knowledge, quality and sustainable results. This is what we have been doing for nearly 100 years.
Our customers have built on Uponor for the past 100 years. We are now building the bridge from a successful past to a sustainable future. With the same innovative spirit that replaced iron and copper with smarter, next-generation piping materials, we are moving forward to ever-more intelligent solutions. Embracing the opportunities of digitalisation. Pushing ahead to new heights of sustainability. Promoting innovative ingenuity in energy saving and intelligent water for the benefit of our customers and the world we live in.
Whether you are looking for a heating, cooling or a reliable heat and water supply system – Uponor has the suitable products. We have a long service life and comply with highest quality and hygiene standards. We contribute to the responsible use of water resources, enhance the quality of life and make sure that energy is used efficiently in all places. We are a partner of specialist installers, designers, investors and end costumers. Uponor experts will be happy to answer all of your questions on the product portfolio or the service range.
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