and contract more than other materials
commonly used for water supply piping.
Therefore, it is important to consider expansion
and contraction when installing these mate-
rials. There is generally enough clearance
around openings, and the runs of pipe are short
enough that thermal expansion does not
become a problem. However, long straight
runs of pipe that are securely fastened at both
ends can become a serious problem. Thermal
expansion is calculated using the formula and
the coefficient of thermal expansion shown in
Figure 20-10. The coefficient of thermal expan-
sion is given in inches per 10°F change in
temperature per 100 feet of pipe.
Assume that a 100′ straight run of PVC
water supply pipe was installed when the
temperature was 60°F. If the temperature rises
to 90°F, how much longer would the pipe be?
Refer to the calculation shown in Figure 20-11.
The increase in length is 1.08″ for the 100′ of
pipe. At a minimum, this causes the pipe to
bend between supports. If the temperature
difference is 50°F, rather than 30°F, the change
in length is 1.80″. At this point, something is
likely to break.
The problem is even greater for CPVC hot
water piping, because the temperature of the
pipe may reach 150°F when hot water runs
through it for extended periods. The calcula-
tions in Figure 20-12 indicate that the total
change in length for a 50′ straight run of CPVC
is nearly 2″. A hot water run could be this long
in some large homes, which prompts a neces-
sary change to prevent failure of the piping.
The solution is to install an expansion loop
near the center of long runs of pipe. The mini-
mum size of the expansion loop depends upon
the amount of thermal expansion and diameter
of the pipe being installed, Figure 20-13. Ex-
pansion loops are made from 90° ells and short
lengths of pipe. The legs of the expansion loop
must be long enough to absorb the change in
length without placing excessive stress on the
pipe or fittings. Therefore, it is important that
these guidelines be followed. If a straight run
360
Section 3 Plumbing System Design and Installation
Figure 20-10. The expansion and contraction of PVC
and CPVC pipe can be calculated using this formula.
Change in
length (″)
=
Expansion
coefficient
×
(High temp. –
Low temp.)
×
Length (′)
100
10
Expansion Coefficient
Material (in./10°F. 100′ length)
PVC 0.360
CPVC 0.380
Figure 20-11. This formula allows you to calculate
how much a length of PVC will expand and contract.
=
×
×
0.360 (90° F – 60° F) 100′
100
=
×
×
0.360 30° F
10
1
10
=
×
10
1
10.8″
=
1.08″
Change in
length (″)
=
Expansion
coefficient
×
(High temp. –
Low temp.)
×
Length (′)
100 10
Figure 20-12. Use this formula to calculate the expan-
sion and contraction of CPVC pipe.
=
×
×
0.380 (150° F – 50° F)
50′
100
1
2
1
2
=
×
×
0.380 100° F
10
10
=
×
10
38.0″
=
1.9″
Change in
length (″)
=
Expansion
coefficient
×
(High temp. –
Low temp.)
×
Length (′)
100 10
Thermal expansion: The result of fluctuating tempera-
tures, causing water supply piping materials to
change dimensions.
Expansion loop: Combination of 90° ells and short
lengths of pipe that are installed near the center of
long runs of pipe as a solution to the thermal expan-
sion problem.