Picking the Perfect PEX Piping Product

By Bob "Hot Rod" Rohr
Radiant Expert

For a brief period of time it seemed that selecting PEX would be as simple as ABC. After the initial blast of polybutylene material came and went, PEX showed up and appears to be here to stay. Indications based on a 25-year or more track record point to a good future for the cross-linked (PE) polyethylene products.

The various PEX manufacturers tout the features and benefits of their particular products and manufacturing methods. After using various brands and types over the years, I have discovered some small differences; differences in installation ease, more than in performance.

PEX A tubing is cross-linked during the extrusion process, called the Engel method (named after Tomas Engel). PEX B uses the silane method. PEX C employs the radiation method, in which the tube undergoes a radiation bombardment. All of these methods provide the cross-linking, turning PE into PEX.

My work has predominately involved radiant heating applications - hydronics in general, including higher temperature (above the typical 120 F radiant but below the listed working temperature of 180 F) applications. If your job requires cold weather applications, the PEX A does "work" better at winter temperatures. The Mr. PEX brand takes flexibility to a new level. The unique cross-linking method used by that product provides for a very bendable tube.

As we cruised along through the middle age of PEX tubing, even more "engineered" products began to gain acceptance. The composite tubes started to gain a foothold. One of the earliest I recall seeing was the Kitec brand from IPEX. It has an additional layer of aluminum laminated within the tube wall. This is now considered a 5-layer tube, with the PEX inner tube, an aluminum layer, two adhesive layers and an outer PEX layer. The aluminum layer provides a substantial oxygen barrier and has the added feature of form stability. It works and handles very similar to soft copper tubing, keeping its shape after being formed.

Other multi-layer brands soon followed, and virtually all of the manufacturers of hydronic tube jumped on the PAP PEX aluminum PEX bandwagon. This product is an excellent tube for piping to remote manifolds and panel radiator homeruns. The ability to shape it to the "route" restrictions, along with the lower expansion and contraction rate, made it a favorite with most of those that tried it. You may find a slightly higher operating temperature range on the multi-layered composite tube.

Various fittings have been marketed to work with the PAP products. The insert crimp fittings employ a single or double o-ring for additional sealing integrity. Often, a longer, typically stainless steel, crimp collar is used. Compression fittings with an external nut and ferrule are also common. Viega recently introduced a product called FostaPEX. An acronym for FOrm STAble PEX, this product is unique in that the aluminum wrap is applied around the full dimension inner PEX tube. It is then covered with a protective PE layer. With the traditional PEX inner tube, there is no need to use an o-ring type insert fitting. This seems to be the "beefiest" of all the hydronic tube products currently available.

Look for the various listing standards on the tube you are considering. ASTM and CSA are two common listings accepted in the United States and Canada.

I use a blend of various brands now, which makes for a colorful jobsite. If the job is a slab tied to remesh, any of the PEX types works fine. I have been trying some of the underslab foam insulation products with the preformed ''posts" to hold the tube. The PAP or FostaPEX product seems to work best with these panels. The tube stays formed, and it does not try to lift or separate the panels. This combination works well regardless of the temperature where you install it.

Save your short scrap pieces to bend into long sweeps to be used as tube protectors where the PEX goes through the slab. Consider asking fellow contractors and wholesalers in your area about their experiences with the different brands. Find a distributor that stocks plenty of tube and fittings for those "need it now" jobs.

If you dare, "Google" around for more data on various products and experiences. Look for nonpartisan, third party, accredited testing and comparison.

Bob "Hot Rod" Rohr is particularly interested in hybrid radiant systems -- systems that utilize solar and wood energy in addition to, or in place of, fossil fuel. Also, systems that incorporate different methods of heat delivery. He owns and operates Show Me Radiant Heat and Solar, Inc. in southwest Missouri. Reach hot rod at hotrodradiant@aol.com or by phone at (417) 753-3998.