formula previously used for PVC and CPVC,
by substituting the appropriate coefficient of
thermal expansion. The following example
illustrates the extent of thermal expansion and
contraction in copper pipe. Assume that a 100′
straight run of copper water supply pipe was
installed when the temperature was 50°F. If the
temperature rises to 100°F, how much longer
would the pipe be? The calculation is shown in
Figure 20-17. The increase in length is 0.564″, or
approximately 5⁄8″, for the 100′ of pipe. This is
sufficient to warrant the installation of a loop.
If the straight run were only 25′, the change in
length is less than 3⁄16″. It is unlikely that an
expansion loop is necessary in this situation.
Understand that every time the pipe cools off,
it decreases in length and expands again when
reheated. This movement places stress on
the pipe and fitting and may be responsible
for some noise in the plumbing system, as the
pipe moves against framing members and
support straps.
The problem is greater when copper is used
for hot water, because the temperature of the
pipe may reach 150°F when hot water runs
through the pipe for extended periods. The
calculations in Figure 20-18 indicate that the
change in length for a 100′ straight run of
copper pipe is about 11⁄8″. It is, however,
unlikely that a straight run of hot water pipe
would be more than 100′ long. The change in
length of a 50′ straight run of copper hot water
pipe may exceed 1⁄2″. This is sufficient to cause a
problem if movement is restricted at both ends
of the pipe run.
Whenever it appears that expansion and
contraction could be a problem, an expansion
loop should be installed near the center of the
run of pipe. The minimum size of the expan-
sion loop depends on the amount of thermal
expansion and the diameter of the pipe being
installed, Figure 20-19.
Chapter 20 Installing Water Supply Piping
363
Figure 20-17. The expansion and contraction of a
copper pipe can be calculated using this formula.
=
×
×
0.1128 (100° F – 50° F)
100′
100
=
×
× 1
× 1
0.1128 50° F
10
10
=
10
5.640″
=
0.564″ or 5⁄8″
Change in
length (″)
=
Expansion
coefficient
×
(High temp. –
Low temp.)
×
Length (′)
100 10
Figure 20-18. The example of copper expansion and
contraction illustrates how increasing the change in
temperature also increases expansion and contraction.
=
×
×
0.1128 (150° F – 50° F)
100′
100
=
×
× 1
× 1
0.1128 100° F
10
10
=
10
11.28″
=
1.128″ or 11⁄8″
Change in
length (″)
=
Expansion
coefficient
×
(High temp. –
Low temp.)
×
Length (′)
100 10
Figure 20-19. This table can be used to determine
what the developed length of a copper expansion off-
set should be. (NIBCO Inc.)
The length of each leg of the offset should be
approximately equal.
Estimated Expansion
Pipe size 1⁄2″ 1″ 11⁄2″ 2″
1⁄2 50″ 70″ 89″ 99″
3⁄4 59″ 83″ 101″ 117″
1 67″ 94″ 115″ 133″
Developed Length of Expansion Offsets (A)
If the estimated expansion for a 3⁄4″ copper pipe is 11⁄2″,
the developed length (A) of the expansion loop should be 101″ or more.
A