Everyone knows that materials expand when they are heated and contract when they get cold. Pipe runs of all standard piping materials, including copper, grow longer when the temperature of the water inside them rises. PEX expands about 10 times as much as copper, which can create relatively large differences in expansion over long runs.
To calculate the linear expansion of PEX tubing, keep in mind that PEX expands 1.1” per 10°F rise per 100 feet of PEX. For example, a 100 foot run of PEX will lengthen by 4.4” if the water temperature increases from 65°F to 105°F. This can cause problems at the point where PEX penetrates a concrete slab. Linear expansion may force PEX to rub against the concrete, and protecting the PEX with a sleeve in this area prevents wear on the tubing. PEX-AL-PEX expands less than standard PEX, and only slightly more than copper.
