Thermal Expansion

Length of Expansion Loop () in Inches Required for 100°F Temperature Change (based on hot water operating @ 140°F)
Pipe Size (in) Length of Run
20 ft 40 ft 60 ft 80 ft 100 ft
1/2 20 29 35 40 45
3/4 24 34 41 48 54
1 27 38 47 54 61
1 1/4 30 42 52 60 67
1 1/2 33 46 56 65 73
2 37 53 65 75 83

All piping systems expand and contract with changes in temperature. This issue must be addressed with appropriate system design to prevent damage to the system. GF Harvel HydroKing® CTS CPVC plumbing pipe will expand or contract approximately 3.8 inches per 100 feet of pipe with every 100°F of temperature rise or fall. The effects of expansion/contraction are usually absorbed by the system at changes of direction in the piping. In other words, long, straight runs of piping are more susceptible to experiencing measurable movement with changes in temperature. As with other piping materials, the installation of an expansion loop or offset is required on long, straight runs, which will allow the piping system to absorb the forces generated by expansion/contraction without damage. The rate of expansion does not vary with pipe size. The effects of expansion/contraction are more pronounced on hot water lines. Generally the amount of temperature change experienced is no more than 100°F. The chart at right can be used to determine the size of an expansion joint needed to compensate for movement when a temperature change of 100°F is experienced.

Loop

Offset

Change of Direction

Hangers or guides should only be placed in the loop, offset, or change of direction as indicated above. Piping supports should restrict lateral movement and should direct axial movement into the expansion loop. Do not restrain "change in direction" configurations by butting up against joists, studs, walls or other structures.

ΔL = 12 yl (ΔT)
where: ΔL = expansion or contraction in inches
y = 3.2 x 10-5 (coefficient of linear expansion )
l = length of piping run in feet
ΔT = temperature change °F
(Maximum temperature - temperature @Installation)

 

Once the change in length (ΔL) has been determined, the length of an offset or expansion loop required to compensate for this change can be calculated as follows:

= Length of expansion loop in inches
E = Modulus of elasticity
D = Average outside diameter of pipe
Δ L = Change in length of pipe due to
temperature change
S = Working stress at max. temperature