5Commercial Applications for PEX

Whether you’ve been in the plumbing business for decades or are new to the industry, one thing is for sure — you’ve heard of PEX. You may not have worked with it yet, but the time could be approaching. It’s best to get ahead of the curve when it comes to installing this piping product that is continuing to gain a foothold in the commercial plumbing world.

Before getting into the important things to know about using PEX on various commercial plumbing applications, it’s helpful to do a rundown of some of the basics about the product.

Crosslinking and Why It’s Important

PEX is an acronym for “crosslinked polyethylene.” The “PE” refers to the raw material used to make polyethylene. The “X” refers to the crosslinking of the polyethylene across its molecular chains.

PEX is manufactured using three different methods, and these different methods create pipe that is crosslinked to varying degrees. PEX-a is 80 percent crosslinked, PEX-b is 65 to 70 percent crosslinked, and PEX-c is 70 to 75 percent crosslinked. These differences in crosslinking affect how the pipe performs and functions in various applications.

Crosslinking makes PEX flexible yet durable. The greater the crosslinking, the more flexible and durable the pipe. For example:

• PEX-a, with the highest degree of crosslinking, offers the tightest bend radius of all PEX. This means the pipe can be bent, instead of using elbows, for each change in direction.
• PEX-a allows kinked pipe to be repaired with a heat gun. That can’t be done with PEX-b or PEX-c.
• The characteristics of PEX-a pipe also allow it to expand up to three times the pipe’s diameter without failure. This makes the pipe highly resistant to damage from frozen water in a system.
• This expansion characteristic of the pipe also makes it ideal for ASTM F1960 expansion fittings. This type of fitting system capitalizes on the shape memory of the pipe that always wants to return to its natural shape after expansion.

To make an expansion fitting, you simply place an expansion ring on the end of the pipe and expand both the pipe and ring with an expansion tool. After the expansion, you immediately insert the fitting. As the pipe and ring shrink back to their natural states, it creates a solid connection that holds tight with 1,500 pounds of radial force.

Keep in mind that there are other PEX connection systems available, such as crimp and clamp fittings. However, these fittings actually work against the properties of PEX. They use a fitting with a smaller internal diameter (which restricts flow), and then they “clamp” or “crimp” down on the pipe. PEX always wants to return to its natural shape. By clamping down on it, it’s forcing the pipe against its natural shape. Not ideal.

Common Commercial Applications

With some basics covered, let’s look specifically at common commercial plumbing applications for PEX:

Risers

PEX for domestic plumbing risers is available in sizes up to 3 inches. When passing through multiple floors, the piping requires fire-penetration sealants, as well as copper tube size (CTS) clamps and iron pipe size (IPS) mid-story guides.

For fire-penetration sealants, a wide range of solutions have been tested and listed for PEX, including intumescent caulks, wrap strips, pass-through devices, collars and cast-in place sleeves. Some firestop manufacturers include — but are not limited to — 3M, Hilti, RectorSeal, Passive Fire Protection Partners, Specified Technologies Inc., and ProSet Systems.

For clamps and guides, domestic cold-water systems require a clamp at the base of each floor, a clamp at the top of every fourth floor and a mid-story guide. Domestic hot-water systems require a clamp at the base of each floor, a clamp at the top of every-other floor and a mid-story guide. Heating hot water and chilled-water systems require a clamp at both the base and top of each floor along with a midstory guide.

In-suite piping

Design layouts for in-suite PEX piping systems can include trunk and branch, home-run, and what the PEX industry refers to as “logic.” Logic plumbing capitalizes on the flexibility of the pipe to bend with each change in direction and incorporates “multiport” tees (essentially a long tee with a series of ports) to minimize connections behind the wall.

In a typical multifamily commercial structure, using a logic design reduces the number of fittings by up to 70 percent, compared with a trunk-and-branch layout. It reduces piping by 40 percent, compared with a home-run system. In addition, it delivers hot water nearly 46 percent faster than a trunk-and-branch system for the first-use fixture and nearly 43 percent faster than a home-run system for the second-use fixture.

Flush banks

In a traditional copper tubing flush bank, the header height is low near the fixture termination point. In a PEX system, it works better to keep the header higher and allow the plumbing lines from the header to the fixture to gradually bend, eliminating the need for a fitting.

There are also fitting options that can help eliminate unnecessary, added connections. For example, a 2-inch multiport tee with three 1-inch outlets does the same job as three reducing tees, but with 45 percent fewer connections. Using this type of multiport tee also reduces the total length required for the pipe and tees by 63 percent.

Plenums

A return-air plenum is an unducted ceiling space being used for air circulation. Some PEX-a piping is listed for use in return-air plenums per ASTM E84. It is important to support the pipe with steel channel segments, also called PEX-a Pipe Supports. These steel support channels are required to be no less than 48 inches long in a return-air plenum, and the space should not have more than 18 inches of bare PEX or fittings. (This also applies to support channels installed in the vertical position.) The pipe can also be installed in return-air plenums with an E84-listed insulation when the use of pipe support is not practical.

Below grade or in the slab

Because PEX piping is available in long, continuous lengths, it is ideal for running below grade or in a slab without fittings. (Always follow local codes; some jurisdictions require additional sleeving and protection.)

For below-grade applications, after placing PEX in a trench:

Be sure to pressurize the system prior to backfilling to check for any damage.

• Backfill with sand or gravel that has a maximum particle size of 3/4-inch. Do not use highly plastic clays, silts, organic materials, or sharp or large rocks as backfillnear the piping.Compact the backfill from the subgrade to a level per local code that will cover the piping 4 inches to 6 inches.
• Most importantly, do not install PEX in soils contaminated with solvents, fuels, organic compounds or pesticides that can degrade the pipe.