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WISRBO PEX Tubing FAQ

PEX is an acronym for cross-linked polyethylene. The "PE" refers to the raw material used to make PEX (Polyethylene), and the "X" refers to the cross-linking of the polyethylene across its molecular chains. The molecular chains are linked into a three dimensional network that makes PEX remarkably durable within a wide range of temperatures and pressures.

The PEX tubing is cross-linked to insure uniform structural integrity and a lifespan of over 200 years. It contains an integral oxygen diffusion barrier on the pipe that is critical to preventing corrosion within the system from the aggressive nature of free oxygen molecules that can readily destroy other types of radiant tubing on the market. We have installed over 1,000 miles of PEX tubing and are convinced the difference in quality is well worth the extra cost over polybutylene (PB) tubing, rubber tubing and tubing sross-linked by the Silane method. The tubing is either installed in the slab of the main concrete pour or stabled to a plywood subfloor and covered with 11/2" of Gypcrete, a lightweight concrete aggregate. It can also be stapled to the underside of floor joists in retrofit installations. The in-slab method has advantages in conductivity, cost, and ease of installation. We have a fool-proof method for installing hardwood floors over the Gypcrete radiant slab.

There are several methods used to cross-link polyethylene. These methods produce products with very different properties. A distinction should be made between PEX produced above the crystal melting temperature ("hot" cross-linking), and PEX produced below the crystal melting temperature ("cold" cross-linking). Simply stated, there's a difference between PEX cross-linked during the manufacturing process and PEX cross-linked as a secondary process.

Wirsbo PEX tubing is made using the Engel method. The Engel method is a "hot" cross-linking process, meaning the actual cross-linking takes place during the extrusion process when the base polyethylene is above its crystal melting temperature.

Engel method PEX is classified within the industry as PEX-A tubing. The Engel method provides more precise control over the degree, consistency and uniformity of cross-linking. This means the tubing is evenly cross-linked, with no weak links within its molecular chains.

Another common cross-linking process is the Electronic or Radiation method (known as PEX-C). In this method, high density polyethylene (HDPE) tubing is extruded. Then, in a secondary process, the tubing is treated with high voltages of electricity. This changes the molecular structure of the polyethylene into a cross-linked network. However, since the electronic method is a "cold" cross-linking process (the material is below the crystal melting point), it produces a lower level of cross-linking than the Engel method. In addition, the Electronic method can produce a less consistent level of cross-linking.

A third common cross-linking process is the Silante method (or PEX-B). This, too, is a cold cross-linking process. A special, pre-mixed polyethylene based resin is extruded into HDPE tubing. In a secondary process, the tubing is placed in a sauna to complete the cross-linking, with more complicated bonds across the tubing's molecular chains.