PexSupply, the online leader in plumbing supplies and heating supplies, provides a helpful explanation of Pex Plumbing.

1. PEX Plumbing
PEX Plumbing is the future of the plumbing industry. It is longer-lasting, less
expensive and easier to install than copper. It is also energy efficient and
environmentally friendly. PEX Plumbing involves PEX tubing, PEX fittings, PEX
manifolds or Plumbing Manifolds, and the PEX Tools that accompany these parts.
These PEX Plumbing resources will help you to learn more about the benefits of
using PEX and how to make the best choices when designing your system.
PEX vs. Copper, Why Choose PEX
There are several reasons why PEX is quickly replacing copper in many plumbing
applications throughout the United States. These include lower cost of material,
the level of difficulty of making connections which also leads to lower labor costs,
the likelihood of pipes bursting, product availability and color coating. The table
below shows the comparison of each item, copper vs. PEX.
Choosing the Right Brand of PEX
AquaPEX, HydroPEX, Viega, Watts, Zurn, the list goes on and on. There are now
more than 20 different brands of PEX tubing for plumbing systems on the market!
It can be difficult to decide which brand to go with and to have a good reason for
the choice. Let's simplify the decision making process:
AquaPEX, made by Wirsbo (Uponor) is the highest quality tubing available on the
market today. AquaPEX is PEX-a tubing and therefore is more homogeneous (with

2. the chemical bonds evenly spread out) making it both stronger and more flexible.
These characteristics come from the Engel production method for PEX-a tubing.
Because of the tubing's strength it is able to hold up better to freezing conditions,
and it can be unkinked using a heat gun. It is also the only brand of PEX plumbing
tubing that can be used with the Wirsbo Expander System.
All other brands of PEX tubing can be looked at as a group. When purchasing
another brand of tubing, be sure the product is being made by a reputable
manufacturer, has at least a 20 year warranty, meets ASTM standards, and meets
the desired pressure ratings. If you follow these guidelines you will come up with
a group of products that includes HydroPEX, Viega PEX, Watts PEX, and Zurn PEX.
When comparing these products, price or brand preference will often be the
deciding factor.
PEX-a, PEX-b, PEX-c - What the Ratings Mean
PEX stands for Poly Ethylene Cross (X)-Linked. It is the cross-linking process that
makes PEX strong, safe and reliable, and it is how this process is done that
determines what grade, or category, the PEX belongs to. Depending on the grade
of PEX that you choose, the flexibility, strength, and uniform nature of the
material will be affected. The letters tell you how the PEX was created and the
quality of the PEX, with A being the highest grade, followed by B, and finally C.
PEX-a
PEX-a is made using the Engel (or peroxide) method to crosslink the molecules of
polyethylene. With this method, the crosslinking is done at a high temperature
above the melting point of the crystals. This "hot crosslinking" produces an
incredibly uniform material with no weak spots. The Engel method produces the
strongest, most flexible PEX tubing possible, allowing for an installation with
fewer joints and fittings than any other type of PEX. PEX-a also features a strong
thermal memory and freeze protection, which means that once the tubing is
expanded or contracted, it will naturally go back to its original shape. Since the
process takes more time and more sophisticated equipment, PEX-a tends to be a
bit more expensive than PEX-b or PEX-c. AquaPEX is the only PEX-a material
available for plumbing applications. Examples of PEX-a for radiant heat include
ThermaPEX and hePEX.
PEX-b

3. PEX-b is made using the Silane (or moisture cure) method. This method performs
the crosslinking with a chemical agent where the process is accelerated using heat
and moisture. This chemical crosslinking is susceptible to some areas where the
bonds are weaker than others and a slightly stiffer final product than PEX-a.
Examples of PEX-b include HydroPEX, Watts PEX, and Viega PEX.
PEX-c
PEX-c is made using the Electron beam (or radiation) method. This method takes
the polyethylene and passes it under an electron beam multiple times in order to
get to the desired level of crosslinking. This is the most energy-efficient method of
creating PEX, but often results in a more brittle, less consistent product than PEX-
a or PEX-b. Electron beam is also the least expensive method and therefore
creates the least expensive tubing.
Which to Choose
When deciding which grade of PEX is right for your application, you should think
about the layout of your tubing. If many tight bends need to be made, it is likely
worth the extra few dollars for PEX-a so that you can avoid breaks in the tubing to
insert elbows. PEX-a is also probably worth the extra money if the tubing will be
exposed to very cold temperatures or to make the installation process easier.
Installation Options
Pex Plumbing system design can be done in a similar fashion to traditional
Plumbing Systems. However, because of its flexibility PEX saves time and money
as compared to installing traditional copper plumbing systems. The options for
running PEX in a plumbing system are listed below, they are not listed in any
preference order.
 Home-run Installation
In this system central manifolds are used to distribute water to all of the
fixtures in a given residence or building. Manifolds may either be valved or
valveless and are generally made of copper or engineered plastic. If they
are valveless, shutoff valves must be used at each fixture. These manifolds
contain between 3 and 12 ports (generally 1/2") to connect PEX Tubing to.
One of the central manifolds will receive cold water, and one manifold will
receive the hot water supply. Each fixture will then have one dedicated cold

4. PEX Tubing line and one dedicated hot PEX Tubing line which begin at the
manifolds. Using this method minimizes the overall number of connections
required. This method also takes advantage of the flexibility of PEX Tubing.
One main benefit of this setup is the reduced time required for hot water
to reach the fixture.
 Remote Manifold Installation
In this PEX Plumbing installation method close-end remote manifolds are
placed near groups of fixtures, i.e. a bathroom. Two manifolds, one hot and
one cold are placed close to the group of fixtures. PEX Tubing is then run
from the manifold to each fixture. Valveless manifolds are typically used,
however valved manifolds may be used as well.
 Structured Plumbing Installation
Structured PEX Plumbing systems make use of the recirculation of hot
water. Manifolds in this system will be located near groups of fixtures. For
the hot water lines, open ended manifolds are used. By doing this, the hot
water return line is created as an extension of the hot water supply line.
This system's main benefit is a reduction in the usage of water and energy
due to the on demand recirculation.
 Modified Home-run Installation
This method is similar to home run installation, but it uses several flow-
through manifolds instead of central manifolds. These open ended
manifolds may be either valved or valveless. This method uses less PEX
tubing than the home run method and may provide hot water faster than
other installation methods.
 Run-and-Branch Installation
This method is also referred to as "teeing off". It is commonly used in rigid
plumbing systems such as copper and CPVC. A PEX fitting such as a tee or
elbow is used each time the tubing needs to be split or change direction.
This method requires more connections than other methods of PEX
Plumbing. This method does not take full advantage of the flexibility of PEX
Tubing.
For all of these installations the system should be inspected and pressure tested
prior to being filled with water. The system should be pressure tested to between
40 and 60 psi.