Over the years, the art and science of plumbing
has changed dramatically. From the first Terra Cotta pipes in
about 1700 B.C. to the newest PEX pipe technology today, no
building is complete without plumbing. If it weren't for
plumbing and plumbing professionals, the urban sprawl that we
have experienced today would not have been possible. And if it
weren't for pipes, plumbing would not be possible either. In
this article I will discuss and compare the advantages and
disadvantages of many of the pipe technologies that have existed
or currently exist on the market for residential use.
Cast Iron Pipe

In the 1960's cast iron pipes were the most popular form of
plumbing in residential construction. This pipe was cheap and
relatively easy to install for its time. It was also noted for
its strength and ability to withstand high pressures. At the
time, this made it ideal for home installation. Unfortunately
for cast iron, it had one major flaw. This pipe was prone to
failure due to rusting. Most cast iron plumbing systems had at
least one leak within 20 years of installation, but many homes
had more than their fair share of plumbing problems. Cast iron
pipes were also known to leave a metallic taste the water. This
was due to the iron leaching into the water from the rusting of
the pipe. Today, cast iron pipe is no longer used for
residential plumbing because of its faults.
Copper Pipe

Copper is probably the most commonly used plumbing materials in
the United States today. This plumbing material offers long term
durability and stability yet is soft enough to resist shattering
upon impact. Its so durable in fact that copper pipes can even
be used outdoors in both above and underground setting. Another
advantage to copper plumbing is its natural ability to resist
the growth of bacteria. This is important because it helps to
ensure that your water supply is clean and safe to use. And
finally, copper has a very high melting point and is able to
resist deformation. This means that during a house fire, the
plumbing may remain intact and could possibly be reused.
Despite all the great things that copper has to offer, there are
a few disadvantages. The first notable disadvantage is the fact
the copper is expensive to purchase and install. Installation of
this plumbing requires soldering equipment and the skills of a
trained plumber. Copper pipes can also be subjected to major
corrosion if the water it contains becomes too acidic. In
addition to this, copper pipes can leave water with a slightly
metallic taste.
PVC Pipe

Next to copper, PVC pipe is also one of the most common
materials used for residential plumbing applications. PVC is
great because it is an inert and stable material that resists
corrosion. It is also a very cheap material that is quick and
easy to install. A minimal amount of skills and tools are
required to properly install PVC pipes in a home.
The main disadvantages to PVC pipe is that it is very brittle
that can break or crack if miss-handled. This is especially true
for properties located in cold climates. In addition to this, it
can only be used indoors and is not intended for hot water
distribution (it has a maximum service temperature of 140
degrees Fahrenheit). Because of this, care must be taken when
installed near hot items such as furnaces or ovens.
CPVC Pipe
CPVC stands for Chlorinated Polyvinyl Chloride. This yellowish
plastic polymer was invented to handle the higher temperatures
that regular PVC could not. It also is slightly stronger than
standard PVC. CPVC has a few advantages over copper as well. It
is generally a stable compound and will not corrode as easily as
copper pipes can. CPVC also requires about 25% less time to
install than copper does (though it does require more bracing).
However, it is not as easy to install as other plumbing
materials such as PEX.
The disadvantages of CPVC include that it is brittle and it
can't withstand very high temperatures like copper can. Another
disadvantage to CPVC is it's high thermal expansion coefficient.
Because of this, CPVC may not be the best choice for climates
that experience wide variations in temperature. Additionally,
CPVC typically costs about twice as much as standard PVC does.
PEX Pipe

PEX is shorthand for "Cross-Linked polyethylene." This material
is relatively new to the field of plumbing (only appearing in
the USA about 20 years ago) and offers some clear advantages
over other available materials. The first, and most notable,
characteristic about this material is that it is flexible. The
flexibility of the pipe allows installers to avoid many
obstacles while also using less fittings. The speed of
installation is also increased by the fact that the pipe
fittings are generally of the compression type. And finally, PEX
is very good at resisting the effects of freeze and thaw because
of its flexibility.
However, there are some disadvantages to this material.
Installation generally requires the use of extensive bracing and
supports. If not done properly, the pipes can move within the
walls when the water is turned on and off (water hammer). PEX
cannot be used outdoors unless it has a UV blocking coating. PEX
is also a softer material that rodents seem to enjoy chewing on.
This can lead to a sudden and catastrophic loss of water
pressure (and potential water damage) within a home.
Summary
The overall consensus is this: Plastic pipes are the cheapest to
purchase and install, however they generally cannot be used
outdoors and have relatively low service temperatures. Copper is
the way to go if you need to deliver hot water or want something
that this durable and long lasting. Today, many houses are being
constructed using a combination of PEX and copper plumbing. This
combines the ease of installation of PEX with the durability and
strength of copper. This affords new homeowners the best
combination of advantages that the residential plumbing industry
has to offer.
Below is a table which summarizes the key characteristics and
information for the various types of plumbing materials for
comparison purposes.
Comparison of Properties for Common Pipe Materials
|
Cast Iron |
Copper (Type M) |
CPVC (Schedule 40) |
PVC (Schedule 40) |
PEX (Class A) |
Cost |
N/A |
$3.90/ft |
$0.83/ft |
$0.20/ft |
$0.46/ft |
Pressure Rating @ 73°F |
200 psi |
225 psi |
400 psi |
100 psi |
150 psi |
Pressure Rating @ 180°F |
200 psi |
120 psi |
100 psi |
N/A |
100 psi |
Max Service Temp |
200 °F |
200 °F |
200 °F |
140°F |
200 °F |
Softening Point (Vicat Test) |
N/A |
N/A |
295 °F |
250 °F |
255 °F |
Melting Point |
2,300 °F |
1,981 °F |
428 °F |
360 °F |
270 °F |
Thermal Expansion |
0.000006 in/in/°F |
0.000009 in/in/°F |
0.000037 in/in/°F |
0.000028 in/in/°F |
0.000083 in/in/°F |
Tensile Strength @ 180°F |
25,000 lbs |
34,800 lbs |
8,700 lbs |
6,500 lbs |
1,806 lbs |
Weight |
12.2 lbs/ft |
0.33 lbs/ft |
0.23 lbs/ft |
0.21 lbs/ft |
0.1 lbs/ft |
Specific Gravity |
7.89 |
8.96 |
1.54 |
1.4 |
0.94 |
Corrosion Resitance |
Low |
Medium |
High |
High |
High |
Life Expectancy |
20-75 years |
50-75 years |
75-100 years |
75-100 years |
75-100 years |
Flexibility |
None |
Slight |
Slight |
Slight |
High |
Thermal Conductivity |
3.8 Btu in /h ft² °F |
19.2 Btu in /h ft² °F |
1 Btu in /h ft² °F |
1.1 Btu in /h ft² °F |
3.2 Btu in /h ft² °F |
Specific Heat |
0.11 Btu/lb °F |
0.09 Btu/lb °F |
0.2 Btu/lb °F |
0.25 Btu/lb °F |
0.55 Btu/lb °F |
The data for this table was compiled from more than 100
resources including textbooks, websites, and other technical
guides.
Properties given are for 3/4" or equivalent pipe except for Cast
Iron which has a diameter of 3 inches.
Joining Method and material will govern the pressure rating for
copper. In this table, a 50-50 tin/lead solder is used because
it is the weakest of all the common copper joining methods.
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