With each new project, more and more professionals are designing with and installing PEX for plumbing
applications to meet tight schedules, tight budgets
and, most importantly, high performance criteria. While
the word is getting out that PEX is the faster, more
cost-effective piping material for plumbing installs, it’s
important to know the characteristics of PEX to best
utilize this product.
You may not know this, but there are
actually three types of PEX — PEX-a, PEX-b
and PEX-c — based on their manufacturing
methods. PEX-a is considered the superior
PEX of the three as its manufacturing
method creates uniform crosslinking for
greater flexibility and increased thermal
and elastic memory in the pipe which
offers kink reparability and the use of
ASTM F1960 expansion fittings.
Hanger spacing and supports
Different installation practices apply for horizontal and
vertical runs of PEX piping. For horizontal installations,
use copper tube size (CTS) hangers, and support the
bare PEX according to the applicable code. Depending
on the pipe size and code, space the hangers between
32 inches and 48 inches apart.
Vertical installations are classified as either in-wall
or riser applications. Again, use CTS hangers, and
support the bare PEX according to the applicable code.
For in-wall installations, space hangers 5 feet apart. For
risers, which run between building stories, install a riser
clamp at the base of each floor and include a mid-story
guide to maintain piping alignment in the stud cavity.
To increase spacing between hangers, use a PEX-a
Pipe Support product. This is a galvanized steel channel
that provides continuous support in suspended-piping
applications. Used appropriately, PEX-a Pipe Support
will allow hanger spacing similar to that of copper, or
between 6 and 8 feet.
Thermal expansion and contraction
PEX-a pipe expands and contracts at a rate of 1. 1
inches per 100 feet per 10°F ∆T. Using PEX-a Pipe
Support, in conjunction with anchor points, can reduce
this expansion and contraction rate to acceptable levels.
Anchor points are required every 65 feet for domestic
hot water and 150 feet for domestic cold water applications. With a loop and clevis system, using PEX-a Pipe
Support and anchoring with fixed points reduces the
rate to 0.22 inches per 100 feet per 10°F ∆T, or by 75
percent. In a strut system, the same procedure reduces
the rate to 0.04 inches per 100 feet per 10°F ∆T, a
93 percent reduction. (Interestingly, the strut scenario
actually reduces the expansion-contraction rate to less
than copper’s, which is 0.11 inches per 100 feet per
As already noted, use a CTS riser clamp on the base
of each floor to control for expansion and contraction
in the risers. For hot water, add an extra clamp at the
top of every other floor. For cold water, add a clamp at
the top of every fourth floor. Also, use an iron pipe size
(IPS) support for mid-story guides to guide the pipe and
Public fixtures — PEX-a is ideal for use with public
fixtures, such as urinals and water closets with flush
valves. It can reduce surge pressures by 18 to 40
percent compared to metallic piping. PEX-a also has
superior acoustical properties, absorbing 10 to 100
times more sound, measured in decibels per centimeter, than metal piping.
Fire-resistant construction — PEX-a piping is rated
for up to three-hour fire assemblies per ASTM E119.
Listings include assemblies for combustible wood-frame
construction as well as non-combustible steel-frame
and concrete construction.
Plenum installations — Some PEX-a piping is
listed for use in return-air plenums per ASTM E84. It
is important to have PEX-a Pipe Support segments no
less than 48 inches long in a return-air plenum, and the
space should not have more than 18 inches of bare
PEX or fittings. This also applies to PEX-a Pipe Support
installed in the vertical position. The pipe can also
be installed in return-air plenums with an E84-listed
insulation when the use of PEX-a Pipe Support is not
Through-penetration firestops — PEX-a pipe carries
numerous listings through ASTM E814 for through-penetrations. Listings range from one-hour penetrations
for combustible wood-frame construction to three-hour,
non-combustible listings for steel-frame and concrete
Underground distribution — PEX-a meets American
Water Works Association (AWWA) C904 requirements
for water service and is rated for direct burial. In below-grade applications, PEX-a can be run continuously to
the desired termination points (use 1-inch insulation to
overcome soil compression).
To learn more about commercial plumbing with PEX-a
pipe, visit uponorengineering.com.
What you should know about commercial PEX plumbing systems