PEX pipe works in a wide variety of heating and plumbing applications, offering major benefits including cost savings. In the decades following the introduction of PEX, manufacturers developed a variation of PEX that includes a layer of aluminum. PEX-Aluminum-PEX, generally referred to as PEX-AL-PEX or PAP, contains an aluminum layer between two layers of PEX. It can frequently be identified by its orange color. The aluminum gives the pipe added rigidity and shape retention.
Since the aluminum creates a natural oxygen barrier, PEX-AL-PEX is a natural choice for hydronic space heating applications (including baseboards and radiant heat). Most PEX-AL-PEX is not code-approved for use with potable water. The lack of an external EVOH oxygen barrier means that the pipe does not require a non-friction layer to prevent noise in joist installations.
PEX-AL-PEX provides several other advantages. Its larger inside diameter than standard PEX causes less of a reduction in flow. PEX-AL-PEX normally has higher temperature and pressure ratings than standard PEX, allowing it to perform in a wider variety of jobs.
Linear expansion, often overlooked, is another area in which PEX-AL-PEX excels. PEX-AL-PEX expands linearly significantly less than standard PEX as the fluid inside heats up. Its expansion coefficient is closer to that of copper pipe.
Options for PEX-AL-PEX fittings include compression assemblies and PEX-AL-PEX press fittings. Prior to making connections, PEX-AL-PEX must be prepped with a chamfering tool of the appropriate size. The tool creates a beveled edge and allows the fitting to set properly.
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