PEX-AL-PEX The most expensive of the bunch, PEX-AL-PEX, also known as aluminum-barrier PEX, features a special construction—namely, an aluminum layer that goes a long way to help the tubing keep its shape once bent.  That means PEX-AL-PEX eliminates the need for the installer to employ tie-downs every few feet.  In addition, because the aluminum layer doubles as an oxygen barrier, PEX-AL-PEX often plays a role in heating systems whose components would corrode if exposed to oxygen.

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 pipe provides several other advantages.  Its larger inside diameter than standard PEX causes less of a reduction in flow.  PEX-AL-PEX tube 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 piping excels.  PEX-AL-PEX  tubing 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 pipe must be prepped with a chamfering tool of the appropriate size.  The tool creates a beveled edge and allows the fitting to set properly.

PEX-Aluminum-PEX (PEX-AL-PEX) tubing contains a layer of aluminum embedded between two layers of PEX.  The aluminum serves as an oxygen barrier and makes the tubing more rigid. See the chart below for some of the the advantages and disadvantages associated with PEX-AL-PEX tubing relative to standard PEX tubing.

Advantage :

•           PEX-AL-PEX  pipe has a larger inside diameter than standard PEX, thus causing less of a reduction in flow

•           PEX-AL-PEX pipe expands less than standard PEX linearly as fluid heats up. Its expansion coefficient is closer to that of copper pipe.

•           PEX-AL-PEX pipe normally has higher temperature and pressure ratings than standard PEX

•           No EVOH oxygen barrier is applied to the outside of the pipe. Standard oxygen-barrier PEX with a non-friction layer (a feature that not all styles have) is necessary in many types of joist installations to minimize noise.


Oxygen Barrier PEX

Since oxygen can cause many heating system components to rust and corrode, baseboard or radiant heating applications require the use of oxygen barrier PEX, offered in grades of PEX-A and PEX-B. The 1/2-inch size is most commonly used; 3/8-, 5/8- and 3/4-inch sizes are also available.

Aluminum Barrier PEX

Also known as PEX-AL-PEX pipe , aluminum barrier PEX is three-layer tubing that consists of a layer of PEX, a layer of aluminum, and another layer of PEX. Its primary benefit is that once bent, PEX-AL-PEX pipe holds its shape and doesn’t need to be tied down every few feet.

The aluminum layer doubles as an oxygen barrier, which in concert with its lower expansion rate, makes PEX-AL-PEX pipe suitable for use in outdoor, warmboard, or high-temperature heating systems.



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