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What is PEX Tubing?

PEX is an acronym for polyethylene crosslinked, or P-oly, E-thylene, X-Linked (PEX).  It was originally invented and created in the 1950’s, but the product wasn’t truly perfected until the 1960’s, and is made to last for about 200 years!  PEX was widely adopted by The Europeans during the early 70’s for their radiant floor heating or hydronic radiant floor heating, providing a great product history for durability and dependability, as the majority of the PEX installed in Europe is still being widely used today.  It is not really known why America is just starting to widely adopt the usage of PEX for hydronic and plumbing needs in residential, commercial and even industrial needs, as it has been around since the 1980’s.  But it is believed the wide adoption is because, there are so many advantages of PEX over copper, like replacing copper with PEX, and other antiquated plumbing products, as PEX is flexible, resists corrosion and offers potential freeze-damage potential, just to name a few advantages.  Along, with why we exist here at Ambient Floor Heat is because of the increasing demand and want for radiant heating systems throughout the United States.  That is why this article will explain the following:

  • The difference between PEX Piping and PEX Tubing; with their references to PEX Plumbing.
  • The different types of PEX: (PEX-A, PEX-B, and PEX-C)
  • The advantages of PEX versus traditional plumbing products.


What’s the Difference?

The terms of PEX tubing and PEX piping have been used interchangeably throughout the industry, that it is commonly even being referred as just PEX plumbing now.  However, manufacturers have been taking the time to distinguish the difference between PEX tubing and PEX piping, since PEX has been around for over 50 years now, there has been many different methods that have been developed for manufacturing PEX.  For example, PEX tubing can be manufactured to the CTS-OD (copper tubing size, outside diameter controlled) sizes with the SDR-9 (standard dimension ratio) or the standard thickness for PEX.  While, PEX piping can be manufactured to IPS-ID (iron pipe size, inside diameter controlled) sizes that vary in thickness to meet the pressure requirements of the ASTM (American Society & Testing Materials) Standards.


The easiest way to remember the difference between PEX tubing and PEX piping is based on the way it is manufactured inside (PEX piping) and outside (PEX tubing) and that’s truly the only differentiating factor between the two types of PEX.  But, PEX tubing (CTS-OD) is the most commonly manufactured PEX tube now, as it is available in all the needed plumbing sizes of 3/8” (three-eighths inch), 1/2” (half-inch), 5/8”(five-eighths inch), 3/4” (three-quarters inch) and 1” (one inch).  A benefit of PEX tubing and/or piping is that manufactures have the ability to color the PEX during the manufacturing process to any color, but predominately use red and blue colors, to provide the ability to differentiate between the hot (red) and cold (blue) water supply lines in the building, be it a homeowner or a plumber. 




PEX Manufacturing

In the 1930’s, a group of British scientists accidently discovered a material, known as High-Density Polyethylene (HDPE), which has allowed the creation of PEX tubing and PEX piping, through a specialized manufacturing process of three-dimensional linking between the molecules, determines the type of PEX plumbing that is made based on how the manufacturer chooses to link the molecules together to determine the final product of PEX.  This process is absolutely critical, because if all the molecules are linked together, it would make the PEX tubing or PEX piping too brittle; and if too few molecules are linked together it’ll just be a weaker form of HDPE, and not PEX tubing or PEX piping at all.  There has to be just the right combination of linked and non-linked molecules for PEX tubing and PEX plumbing to exist.


The 3-Types of PEX

There are more than 20 different types of PEX in the market, but we will focus only on the three most popular types of PEX, with them being PEX-A, PEX-B, and PEX-C.  Please note, the letters aren’t grades, but simply the identification manufacturing process used to make the PEX tubing and piping.  

Engel-Method (PEX-A) - This is named after the Tomas Engel, the inventor of PEX, as he was a European scientist that discovered PEX through experimentation, and that in this method the PEX becomes crosslinked while the HDPE is still in its melted form, and peroxide is added to the mix during this process, while a tremendous amount of pressure and high temperature are added to the liquid.  When the crosslink bond occurs the PEX tubing that comes out, in the extrusion process, is as clear as glass, but as it cools the color that the manufacturer added to the mix appears (as discussed above for making the PEX red or blue) once it is fully cured and dry.  Even though this PEX-A may cost a bit more than PEX-B and PEX-C, it has the highest resistance to cracking and long-term prevention for oxidation.  PEX-A has been used for over 50 years and has little to no known major issues during this time and this process is known to be the best way, or is considered the superior method in the industry to make PEX tubing or PEX pipe, to this day!  Tomas Engel, was a true visionary, inventor and innovator.

Irradiation-Method PEX (PEX-C) – The process to manufacture PEX-C needs to be in a fully-controlled process, since if the process is not completed properly, it will result in a less uniform crosslinking, and the cause of it is that the irradiated PEX tube or PEX pipe can become brittle and weak on the outer-layer making it more susceptible to a failure rate.  However, with advances in manufacturing, this is no longer the case at all.  As the breakdown occured during the process when the PEX tubing is ran through an electron beam cannon at the final step in the manufacturing process, as this is when the crosslinking of the material occurs, instead of during the pressurized process, like in PEX-A.  PEX-C is the most environmentally friendly production of PEX as it does not involve the use of chemicals and high-energy to create the molecular bonding process.

Silane-Method (PEX-B) – The Silane method of crosslinking consists of bonding silicon and oxygen molecules together, instead of the other two methods with Engel and Irradiation method that crosslinking carbon molecules together.  It is supposedly claimed that this Silane method is weaker, than carbon-carbon molecular links, and it may have an effect on the longevity of the PEX-B tubing and PEX-B piping, because of the chemical stability, but we probably won’t find out soon, since as stated earlier, PEX tubing can last to over 200 years!

Oxygen vs. Non-Oxygen Barrier PEX

It is imperative to understand the application that the PEX tubing or PEX piping is going to be used for in either plumbing, hydronic radiant floor heat or other applications.  This is because, even though PEX is highly versatile, you still need to ensure that the right materials are used for the project!  Since, in most plumbing projects, as these primarily involve the use of potable water, non-oxygen barrier PEX is used for these types of situations.  However, radiant floor heating or hydronic heating systems, include components that can rust and corrode if exposed to oxygen, as non-oxygen barrier PEX (Standard PEX) allows oxygen to seep through the tubing or piping and eventually corroding, rusting and destroying your hydronic heating system!  Hence, understanding the importance of the different varieties of PEX available, so that using an oxygen barrier PEX tubing or PEX piping for your radiant floor heating system, prevents any damage to your investment!


PEX Advantages

  • Flexible: The flexibility of PEX allows for easier installation, with less connections or fittings means reduced chances of leaks in your plumbing system versus traditional plumbing that requires so many connection points, as PEX can bend 90 degrees without the need for elbow fittings.
  • Resistance: PEX is highly resistant to corrosion, scaling and pitting that can occur with acidic water systems in copper or other metal based plumbing products.
  • Freeze-Resistance: PEX is highly flexible and can expand up to three-times (3x) its size, unlike copper or even plastic piping used in plumbing systems.
  • Metal-Free: PEX is metal free, which means there is no fear of ‘leeching’ metals from copper or other metal based plumbing products that can breakdown over it’s life.
  • Noise-Reducing: PEX allows water to pass through more quietly, and reduces the ‘banging’ noise associated with copper piping plumbing systems from the air not being able to escape like in PEX.  Allowing for a more peaceful and quiet plumbing operation in your home!
  • Environmental-Friendly: PEX fittings and connections do not require soldering, plumbing glue, chemicals, solvents or even a propane torch to make it the safest to install in the industry.
  • Conserves-Energy: PEX does not absorb heat from the hot water lines, like copper pipe does, hence the condensation on copper pipes running hot water, allowing the conservation of energy for your heating lines.  This is why PEX is preferred by Ambient for your Radiant Floor Heat!
  • Cost-Effective: PEX is one of the most cost-effective plumbing systems on the market, with it being cheaper, by about a third of the cost than copper, meaning cheaper material costs.  Along with the fact that it takes less time for installation, meaning cheaper labor costs, and a less likely chance of having a leak to essentially reduce or eliminate any future repair costs.
  • Longevity: As stated in the beginning of the article, PEX is manufactured today to last up to 200 Years!  Meaning that people that aren’t even born today, could be enjoying the same PEX plumbing system that you install today!

These are the primary advantages of PEX plumbing, there are many more in the industry, but these are the most prevalent to take into consideration for PEX versus other plumbing products.



Lastly, just remember that even though PEX is just starting to be widely adopted by the United States, it has been used in over tens-of-thousands of homes, in other countries, mainly across Europe, for over 50 years! With some homes having PEX from over 30 years ago, that is still fully operational and functioning from the first day it was installed!  So, if you hear about problems with PEX plumbing or PEX systems in the United States, it is not because of the PEX, those problems manifest from poor installation, the use of the wrong PEX tubing or PEX piping for the plumbing application (oxygenated vs. non-oxygenated), and wrong fittings being used or installed improperly, rather than the PEX tubing or PEX piping failing or being faulty itself.  Because, all three types of PEX meet the ASTM (American Society for Testing and Materials), NSF (National Science Foundation) and CSA (Canadian Standards Association) standards.

It is hoped that this article was able to explain and provide a better understanding of PEX!

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