The advantages of PEX
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Photo 1: PEX tubing
PEX is a somewhat flexible plastic pipe
that you can run for water supply lines much like copper or CPVC.
PEX, a flexible tubing that comes in long
rolls or sticks, offers many 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, eliminating most elbows and joints. Second, PEX doesn't sweat under
high humidity conditions, and it's
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). Finally, it's super easy to work with, and it's less expensive than copper.
Check with a
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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.
Use the Same Stuff
There are several different manufacturers of PEX. It is very important that
you know which brand of pipes you’re working with and install only that
manufacturer’s connectors and fittings. If you mix and match materials,
you will void your warranty and may fail your inspection. Worst-case
scenario: You’ll end up with leaky pipes, water damage and extremely
unhappy homeowners. Not all products have recognizable markings on
them, so leave a few of the packaging labels on-site to appease the
inspector and for future reference.
Make crimped joints at fittings
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Photo 2: Crimping tool
Make connections with special crimp
fittings in which you clamp a copper
ring around an inner fitting sleeve.
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Photo 3: PEX cutter
Cut the PEX off perfectly square with a special PEX cutter for
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Photo 4: Stab-in fittings
don’t require a special tool, but they’re a lot more expensive. You
simply push the pipe into the openings.
Press the outer ring onto the fitting
to release the pipe.
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 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
Another popular and widely used clamp is the cinch clamp. They’re
readily available and
and you know
the tab of the
clamp will be
Fittings for a shower valve
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Photo 5: Threaded PEX fittings
Use threaded fittings for shower valves. Tighten the fittings before crimping the
PEX. A plastic bracket forms the sharpest 90-degree angle permitted for this
brand of PEX.
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Photo 6: PEX shutoff valves
Crimp PEX shutoff valves into the
hot and cold lines.
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Photo 7: Drop-ear elbow
Use drop-ear fittings designed for PEX
for the shower arm and tub spout.
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.
PEX is plastic, and plastic
melts. So keep your PEX
pipes away from hot
stuff. Codes commonly
require PEX to be at least
18 in. away from the water
heater and 6 in. away
from single-wall flues on
gas water heaters. And
stay well clear of furnace
flues, wood-burning stove
pipes and any other item
that gets hot.
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.
Repair or replace kinks
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How to fix kinks
Kinks happen. You can repair kinks with a heat gun, but PEX tends
to rekink in the previously kinked spot, especially if the pipe
needs to make a bend at the kinked location. It’s best to cut
kinks out and use the shorter sections of pipe elsewhere. If
you get a minor kink in the middle of a long, straight run
and you don’t want to cut it out, heat the pipe with a
heat gun and then cover the damaged area with a
hanger or abrasion clip (see “Protect Your PEX,” below). That will help the pipe keep its shape.
Protect PEX with abrasion clips and insulation.
Abrasion and suspension clips
Protect Your Pex
PEX expands and contracts with
changes in temperature, which
causes the pipes to move back
and forth. Several years of even
the slightest movement can wear
a hole in PEX pipes, especially if
they're rubbing against something
If your pipe is in contact with a
joist, duct, electrical box or steel
stud, or it is passing through a
block wall or concrete slab, it
needs to be protected. You can protect your pipe with abrasion
clips, cover the pipe with inexpensive pipe insulation, or enclose
it with a larger pipe. Pipes that are encased in concrete (for
in-floor heating, for example) are OK because the concrete
holds them in place. And pipes running straight through wood
studs and joists are fine too—just protect the pipe in areas
where it bends as it passes through.
Transitions to other types of pipe
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Photo 8: PEX transition fittings
Different types of water pipe require different PEX transition fittings.
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
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Photo 9: PEX eliminates joints
Snake a single length of PEX through joists and between floors. It doesn't require
joints unless you have tight turns. Have a helper feed it to avoid kinks in the plastic.
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Photo 10: Support long runs
Support PEX every 24 in. and
at turns with special clamps.
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” 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.
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).
Home runs for supply lines.
Home Runs Are Best
You can install PEX with main lines and branches to each fixture,
but “home runs” are better. A home run is one line that runs directly
to a fixture, starting at a manifold (above). Home runs require
more piping but deliver a stronger and more consistent water flow.
Also, installing home runs is fast and requires only two connections
(one at the manifold and another at the fixture end), which
You can also use a hybrid system where you run 3/4-in. hot and
cold lines to a set of fixtures—for example, in a bathroom—and
install a smaller manifold behind an access panel. Then make
short runs of 1/2-in. lines to each fixture. Another cool thing about
home runs is that each fitting has its own shutoff at the manifold.
That means you can shut off just that fitting to do some work—you
don’t have to shut off the water to the whole house.
Upsize to avoid poor pressure
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Feed PEX from coils
The inside diameter of 1/2-in. PEX is smaller than that of 1/2-in.
copper (and even smaller with fittings). If you're tearing out
copper and replacing it with the same size PEX pipe, the water
flow to the fixtures may be noticeably lower when you're done. If
you're working on a house that has less than 45 lbs. of pressure or
a flow rate of less than 4 gallons per minute, make sure you
install home runs, and consider going up in size to
3/4-in. pipe. A simple way to test water pressure is to hook up a
hose bib pressure gauge (sold at home centers) to your spigot. To
check your flow rate, just see how many gallons of water flow into
a 5-gallon bucket in one minute.
Keep PEX coiled with bungee cords.
Control Your Coil With an Elastic Cord
One complaint about working with PEX is that the coils have a
mind of their own. As soon as the banding is removed from the
coils, they tend to explode out in every direction. To deal with this,
use bungee cords to help keep your coils in check. Leave the
cords on and unroll just the amount you need. If your coil
comes wrapped in plastic, don’t remove it. Sometimes you can
just feed out pipe from the innermost section of the coil. If you
have just a few smaller runs or short lengths to install, buy sections
of straight pipe—it's a lot easier to work with.
Warm up cold pipes
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Keep connections warm during assembly
FYI: If you're installing PEX in the winter in a
building with no heat, and all the pipes and fittings
are freezing cold, expect lots of leaks when the furnace is fired up
and the water turned on. Most PEX manufacturers recommend you
work with pipe at temperatures above freezing.
The whole length of the pipe doesn’t need to be
warm, just wherever you make a connection. You
can heat those cold pipes and fittings with a heat
gun or hair dryer, leave them in a warm vehicle for
a while or keep fittings in your pocket. Heck, you
can even warm a pipe in a thermos of hot water.
Plan for stub-outs in advance
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Photo 11: Attach PEX to stub-outs
Use special copper stub-outs for more
visible locations. Cut off the tube and
mount a standard shutoff valve.
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Photo 12: Use angle fittings for tight turns
Make tight turns with 90-degree
angle fittings. For hidden stub-outs,
use shutoff valves designed for PEX.
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Install PeX dIrectly
You can run PEX directly to the fixtures so you won’t have to
bury fittings behind the walls. If keeping the PEX perfectly
straight where it exits the wall is too hard, use a
90-degree copper stub-out.
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 with an elbow (Photo 12). You can also run PEX directly to the fixtures (see photo).
Whichever method you use, be sure to
add a couple of extra fasteners next to the
stub-out to increase stability.
Avoid Kinks at Tight Corners
PEX's flexibility makes it
easy to work with. It can be
bent around pretty sharp
corners without the need
for an elbow fitting. But if
you try to bend it too much,
you’ll end up kinking it.
Installing a bend support
will prevent this, and it will
also protect the pipe from