When planning a PEX plumbing project, one of the most common questions that
arises is about mixing and matching different types of tubing and fittings.
Specifically, many DIYers and professionals ask: Can you use PEX-B fittings on
PEX-A pipe?
The short answer is yes, you generally can. The most common connection
method for this combination is the cold expansion style, using a PEX-A expansion
ring and an expansion tool.
However, the why and how are crucial for a successful, long-lasting, and
code-compliant installation. This article will clear up the confusion, explain
the science behind the connection, and outline the correct way to join these two
PEX types.
Understanding the Key Difference: PEX-A vs. PEX-B
To understand why the fitting choice matters, you need to know the
fundamental difference between PEX-A and PEX-B.
PEX-A (Engel Method): This is produced using the peroxide (Engel) method.
It results in the most flexible type of PEX, with a unique "shape memory." This
means it can be expanded significantly and will slowly shrink back to its
original size, creating a powerful, mechanical seal around a fitting.
PEX-B (Silane Method): This is produced using the moisture-cure (Silane)
method. It is stiffer and has less shape memory than PEX-A. It's a durable and
cost-effective tubing, but it doesn't expand and contract as effectively as
PEX-A.
The fittings themselves are also designed differently to complement the
tubing's properties.
The Right Way to Connect PEX-B Fittings to PEX-A Pipe
The key to a reliable connection lies in the method, not just the fitting
material. The industry-standard and most recommended way to connect a standard
PEX-B fitting (which is a barbed brass or poly alloy fitting) to a PEX-A pipe is
by using the Cold Expansion Method.
Here’s how it works:
Use a PEX-A Expansion Ring: Slide a PEX-A expansion ring (a special,
oversized ring designed for this method) onto the PEX-A pipe.
Expand the Pipe and Ring: Use a manual PEX expander tool or a powerful
expansion tool to simultaneously stretch the end of the PEX-A pipe and the
expansion ring.
Insert the PEX-B Fitting: Quickly slide the barbed PEX-B fitting into the
expanded end of the pipe until it seats against the ring.
Let it Shrink: The magic of PEX-A's shape memory takes over. The pipe and
ring will contract tightly around the barbed fitting, forming a strong,
360-degree mechanical seal that is often stronger than the pipe itself.
Why This Method is Approved:
This system is covered under the ASTM F1960 standard, which specifically
governs the use of cold expansion fittings on PEX tubing. Major PEX-A
manufacturers (like Uponor) explicitly approve the use of standard barbed brass
insert fittings with their tubing when installed using the expansion method.
Methods to Avoid
While the expansion method is king, it's important to address other common
connection types:
Can you use a Crimp Ring (PEX-B method) on PEX-A pipe? Yes, this is
possible, but it is not the recommended best practice. Crimping works by
compressing the pipe onto the fitting. Because PEX-A is so soft and has strong
shape memory, it will constantly try to return to its original shape, which can,
over a very long time, lead to a reduction in clamping force on the crimp ring.
While many plumbers have done it without issue, for a guaranteed, optimal seal,
the expansion method is superior.
Can you use a Clamp Ring (PEX-B method) on PEX-A pipe? The same logic
applies as with crimp rings. It will likely work, but it doesn't leverage the
primary advantage of PEX-A (its expansion and shape memory), making it a
second-choice option.
Conclusion
So, can you use PEX-B fittings on PEX-A pipe? Absolutely. For the most
reliable, code-compliant, and strongest connection, you should always use the
cold expansion method with a PEX-A expansion ring and the appropriate tool.
This approach fully utilizes the superior shape memory of PEX-A tubing,
creating a monolithic connection that is resistant to fatigue and provides peace
of mind for years to come. While crimping is a fallback, expansion is the
definitive best practice for combining these two popular types of PEX plumbing
materials. Always check your local plumbing codes and the instructions from your
tubing manufacturer before starting your project.
