PEX Tubing Information
In 1968, German scientist Thomas Engle discovered a way to crosslink common plastic (polyethylene) through radiation to produce a much suppler form of the material. The new plastic, fashioned into flexible PEX pipe (also known as PEX tubing), arrived in the US in the 1980s.
PEX tubing has become one of the most common materials used in residential plumbing systems.
The Differences Between PEX-A, -B and -C
When you see PEX-A, PEX-B and PEX-C, you may wonder what the differences are between them and which one you should choose. As many of you know, PEX stands for cross-linked polyethylene. The letter that follows simply signifies the type of manufacturing method used to cross link the polyethylene, not the grade of PEX.
If you look in the international plumbing codes, you’ll only see references to PEX, not the different types. That’s because by and large, all PEX pipes are very similar.
They must all meet the same performance standards. There are some requirements that apply to all PEX pipe used for commercial and residential plumbing applications. Others apply to PEX used in specific systems or applications. A few examples include:
- ASTM F876, which is the performance standard for PEX tubing.
- NSF/ANSI/CAN 61 when installed in water distribution systems.
They’re dimensionally the same. PEX size doesn’t change between PEX-A, -B and –C, as defined in ASTM F876. They’re all Copper Tube Size, or CTS.
They all have a Material Designation Code. All PEX pipe is assigned one of these codes based on their level of chlorine resistance, UV resistance and hydrostatic design basis (HDB), or pressure rating.
So What are the Differences between PEX types? The truth is, not a whole lot. Again, the main distinction lies in the manufacturing method, which is what assigns an A, B or C to PEX.
- PEX A is made using the Peroxide, or Engel, method. This type of PEX is the most flexible of the three types. It expands to the greatest degree when subjected to freezing water and it’s easy to work with, but it’s more expensive than B or C. Other than flexibility, PEX-A has no significant benefit over PEX-B.
- PEX B is formed using Silane, or Moisture Cure, method. This is the most common PEX pipe type out there. This type of PEX is slightly stiffer than PEX-A, and has a distinct coil “memory” that makes the tubing want to return to its original coiled state. It also expands to resist cracking when water freezes but is less expensive than PEX-A. PEX-B also features an increased resistance to chlorine, making it a good choice in areas where water is highly chlorinated.
- PEX C is created using the Electronic Irradiation, or Cold, method of cross-linking. Because it’s the stiffest version, PEX-C is the most difficult to work with; this stiffness also makes it most prone to kinking, as well as susceptible to cracking when water freezes.
- PERT is polyethylene raised temperature tubing and is made with Hypertherm PE-RT resins from The Dow
Chemical Company. PERT offers improved flexibility with relaxed memory for less spring back than PEX. PERT is recyclable and requires less energy to produce than PEX. PERT provides increased flexibility and excellent hydrostatic strength at high temperatures and burst pressures that surpass required industry standards
There may be small variations in density, burst pressure levels and bend radiuses between PEX pipe types, but they’re negligible. There are, however, a couple of key differences to pay attention to no matter which PEX pipe you’re looking at.
The Material Designation Code:
This four-digit number changes depending on the chlorine resistance rating and UV resistance rating as determined in ASTM F876. It can be broken down into three parts:
- The first digit is chlorine resistance. The highest rating is a Class 5.
- The second digit is UV resistance. The highest rating is a Class 3, which indicates a six-month UV resistance.
- The last two digits is the HDB, which is the same for all the PEX tubing sold in the U.S. This will be “06,” indicating a 630 HDB, or a pressure rating of 160 psi at 73 F.
- The highest code is PEX 5306
| Nominal ID | OD | Wall Thickness | Avg. ID | Bend Radius | Volume gal/100′ | Weight lbs/100ft |
|---|---|---|---|---|---|---|
| 1/4″ | .375 | .0625 | .250 | 3″ | 0.250 | |
| 3/8″ | .500 | 0.070 | .350 | 4″ | 0.500 | 4.5 |
| 1/2″ | .625 | 0.070 | .475 | 5″ | 0.921 | 5.8 |
| 3/4″ | .875 | 0.097 | .681 | 7″ | 1.837 | 11 |
| 1″ | 1.125 | 0.125 | .862 | 19″ | 3.025 | 17.06 |
| 1-1/4″ | 1.375 | 0.160 | 1.054 | 11″ | 4.530 | 25 |
| 1-1/2″ | 1.625 | 0.190 | 1.244 | 13″ | 6.320 | 35 |
| 2″ | 2.125 | 0.236 | 1.653 | 17″ | 11.15 | 60 |