Step into just about any house built in the past 50 years, and
odds are, you're going to see one of three materials used for the
water supply lines: copper, steel or CPVC. While these three
materials are reliable and fairly easy to work with, a flexible
tubing called PEX (“cross-linked” polyethylene) has become
popular with many plumbers. PEX has been used for many
years for in-floor heating systems but only more recently for
supply lines. You may find it in a newer home, and, since it's
easy to work with, you might consider it as an alternative to traditional
materials when running new water lines. It's now available
at many home centers. In this article, we'll introduce you
to PEX and show you the basic techniques for working with it.
The advantages of PEX
PEX, a flexible tubing that comes in long
rolls, offers several advantages over traditional
piping. First, you can usually make
long continuous runs, eliminating most
elbows and joints. You can snake long
runs through joists and studs. Second, PEX doesn't sweat under
high humidity conditions, and it's also
resistant to bursting, even if the lines
freeze solid. Third, joints are easier. You
add fittings simply by crimping metal
rings over barbed fittings using a special
crimping tool. Crimping takes seconds
and is virtually error-free, avoiding the
hassle of soldering (copper) and the
fumes and mess of cementing (CPVC).
However, PEX has a couple of drawbacks.
First, the crimper is expensive. You can sometimes rent one, but each manufacturer
wants you to use its proprietary
crimping tool for its tubing. The rental
store might not carry the right one. A second drawback is a somewhat sloppy
appearance. And third, the fittings are
more expensive than for copper and
CPVC systems. The overall cost of materials
is about the same as for other systems.
Some home centers may stock more
than one brand of PEX. Buy the same
brand of pipe, fittings and tools to ensure
Check with a
from what we
Make crimped joints at fittings
The heart and soul of the PEX system is
the barbed fitting/crimping ring combination
(Photo 2). There's no need for
solder, glue or pipe wrenches—just
position the crimping ring over the end
of the PEX pipe, slide the pipe over the
barbed fitting and use the special crimping
tool to compress the ring. Just be
sure to center the ring over the barb and
depress the crimping tool's handles
That's it. The resulting seal is watertight.
The crimping tool shown can be
used for both 3/4-in. and 1/2-in. crimps,
important when you're running several
sizes of pipe. If you make a mistake in
crimping, you can use a special decrimping
tool to remove the ring and
then reuse the fitting. A clean, square cut
is essential for a proper seal; the PEX cutter
shown in Photo 3 works great
and is available anywhere PEX is sold.
Another type of fitting for joints,
called “stab-in” fittings (Photo
4), is also sometimes available. You simply
push the ends of the PEX into the
fitting, where it locks in place. These fittings
are available for most situations,
including joining PEX to copper and to
CPVC. However, we don't recommend
them unless you have easy future access
to the joint.
Fittings for a shower valve
Most shower valves have threaded ports
for the supply lines. Tighten the threaded
fittings into the shower valve before
crimping on the PEX line. Then run the
lines through the studs (Photo 5), make
90-degree turns with a plastic or metal
elbow sleeve, or crimp in right-angle fittings
in tight quarters (Photo 12).
Splice in shutoff valves as well (Photo 6).
Then, install “drop-ear elbows” to stabilize
the spouts and/or showerhead assemblies,
just as you normally would (Photo
7). Once you've secured your drop-ear
elbows and threaded fittings, run the PEX
line between the valve and the drop-ear
elbows and crimp each joint.
Although PEX can be used for hot
water supply and in-floor heating,
it can melt if run next to exhaust
vents on water heaters. Use special
18-in. copper extensions if
you run PEX near these vents.
Since PEX won't burst when it
freezes, you might be tempted to
use it for seasonal dwellings,
such as cabins. PEX is soft, however,
and rodents could chew
through exposed lines.
Transitions to other types of pipe
If you're adding a guest bath or finally getting
to that laundry tub you've been
promising for the past five years, you'll
have to join PEX to the existing system.
Make sure you shut off the main water
supply, then drain the lines. Use the special
transition fittings shown to transition
from copper, CPVC or steel. Solder,
glue or thread on the transition fitting,
then crimp PEX line on the barbed fitting.
Plumbing codes vary on allowing
brass/steel connections. If they're allowed,
be sure to apply liberal amounts of both
Teflon tape and pipe joint compound to
prevent reaction between the two metals.
Run the line without joints
You can run PEX line a couple of different
ways. Most often, you run PEX as you
would in a conventional plumbing system,
with 3/4-in. main lines and 1/2-in.
branch lines (Photo 1). You can also
use a “manifold” system, where you run a
1/2-in. line to each fixture from a central
spot. But we won't show that system here.
Run your main lines first—don't worry
about cutting in your branch lines yet. If
you're running PEX through joists or
studs, drill 3/4-in. holes for 1/2-in. piping
and 1-in. holes for 3/4-in. piping. You
don't have to drill holes in an exact
straight line; there's enough flex in the
pipe to feed it through misaligned holes.
Have a helper feed the line to avoid kinks
and snarls (Photo 9). Where the pipe
runs along a surface, be sure to support it
every 16 to 24 in. to reduce sag and give
the piping a neat appearance (Photo 10).
Some manufacturers recommend adding
“suspension clips” (not shown) at each
hole to prevent abrasion. You must use
suspension clips for PEX that goes
through metal studs, and nail protection
plates when the tubing runs within 1-1/2
in. of the face of a stud or joist.
Once you've run your main line, go
back and mark the location of each
branch line with a marker, leaving a 1-in.
gap for the barbed tee. Cut the 1-in. gap
out of the main line, crimp your tees into
place and run your branch lines to the
appropriate fixtures. This
eliminates the need to measure each section
of main line and makes installation
both faster and easier.
You can generally flex PEX into gradual
bends without risking a kink (Photo 10).
When you need to turn a corner, many
times you can bend the pipe manually
and eliminate the need for an elbow. But
different brands of PEX have different
“kinking” points, so always read the manufacturer's
guidelines. Buy special plastic
or metal elbows (Photo 5) to make
the tightest recommended turns virtually
If you need to make a really sharp
turn, cut the line and use a copper
90-degree ell (Photo 12).
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Plan for stub-outs in advance
There are a couple of options for bringing
PEX out through a wall (stub-outs). If the
piping is going to be exposed, say for a
pedestal sink or a toilet, buy a copper
stub-out and crimp it onto the PEX
(Photo 11). Then use standard shutoff
valves. If the stub-out will be hidden,
inside a cabinet, for example, or you don't
mind the look of exposed PEX line, use a
barbed PEX shutoff valve (Photo 12).
Whichever method you use, be sure to
add a couple of extra fasteners next to the
stub-out to increase stability.