PEX TUBING

In assessing hydronic warm-floor heating systems, be very careful. The tubing is the single most important element of the system and not all tubing is the same. Shelter Technology uses only Wirsbo PEX, the industry leader and the only tubing with a spotless track record. There are brands of cheaper tubing using the name "PEX", but it is not the same. The Wirsbo PEX is cross-linked polyethylene with an oxygen infusion barrier. It has been used in Europe for 30 years, with more than 4 billion feet of installed tubing performing without a single incidence of product failure.  500 million feet of that is in North America alone.  Samples of the tubing have been under high temperature and pressure continuously since 1973, with no sign of decreased performance. Tests, both by Wirsbo and independent sources, predict that the Wirsbo PEX tubing should have a system life in excess of 100 years

The Wonders of Cross-Linking

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, pressures and chemicals.

There are several different methods used to cross-link polyethylene. It is important to distinguish between the various methods of cross-linking and the PEX products that result. A distinction should be made between PEX produced above the polyethylene crystalline melting temperature, and PEX produced below that temperature. Simply stated, there is a difference between PEX that is cross-linked during extrusion and PEX tubing that is cross-linked in a post-extrusion process.

Wirsbo uses the Engel method to chemically cross-link polyethylene during the manufacturing process when polyethylene is in its amorphic state (above the crystalline melting point). The Engel method provides more precise control of the degree of cross-linking resulting in a perfectly uniform product. There is no chance that areas of the tube will be unevenly cross-linked, and there are no weak links in the molecular chain. Engel Method PEX has what is known as shape or thermal memory. It is this thermoelastic property that gives Wirsbo PEX (Engel) its incredible flexibility, strength, and high temperature/pressure resistance. The shape memory is also what allows the ProPEX Fitting system to work.

The other two common methods of cross-linking PEX are the Radiation method and the Silane method. Radiation cross-linked PEX uses electrons that bombard the tubing after it has been extruded. Silane PEX uses a warm bath to cross-link, and then flushes the tubing to remove contaminants. Silane PEX is not as evenly cross-linked as Engel PEX, nor does it have the same degree of thermal memory.

Stress Resistance -- Tubing installed in panel heating applications must be capable of withstanding the extreme stresses that result from installation within a concrete slab, or on a structural wood floor. Typical stresses include: Expansion and contraction that result from repeated heating and subsequent cooling of the heat transfer fluid, mechanical abrasion, shearing and stretching that occurs as a result of installation, normal structural movement and heating and cooling from seasonal weather changes. Wirsbo PEX, because it is cross-linked, is uniquely capable of withstanding the stresses that occur in radiant floor heating and plumbing. 

Testing

Wirsbo PEX (Engel) for radiant floor heating, plumbing and snow-melting is proven the best in the industry through over 25 years of use in the field and the most extensive testing programs in the industry. Every coil of Wirsbo PEX tubing undergoes testing for strength, chemical and thermal resistance and percentage of cross-linking. In fact, Wirsbo PEX tubing currently holds the unofficial world record for long-term testing at elevated temperature and pressure -- 26 years at 203° F at 151 psi, and still going. When the test is completed, the record will be official.

Extrapolation of long-term testing on Wirsbo PEX tubing shows that Wirsbo PEX will have a system life in excess of 100 years.

Standards, Listings and Certifications

Wirsbo PEX tubing is currently manufactured to ASTM F876 and ASTM F877 as certified by Hauser Laboratories and the National Sanitation Foundation (NSF). It is rated at 73.4° F at 160 psi, 180 ° F at 100 psi and 200 ° F at 80 psi. These pressure and temperature ratings are issued by the Hydrostatic Design Stress Board of the Plastic Pipe Institute, a division of the Society of Plastics Industry. Wirsbo PEX and fittings are certified to be in compliance with the Canadian Standards Association Standard CAN/CSA 137.5M, "Cross-linked Polyethylene (PEX) Tubing Systems For Pressure Applications."