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Q&A Spotlight

Making the Best PEX Connections

Is a crimped connection with Uponor PEX A guaranteed to leak, or have plumbers learned differently?

Image 1 of 4
Zurn Industries produces the components for this crimped connection in PEX tubing, calling it the QickCap Copper Crimp Ring System. [Photo credit: Zurn Industries]
Image Credit: Image #1: Zurn Industries
Zurn Industries produces the components for this crimped connection in PEX tubing, calling it the QickCap Copper Crimp Ring System. [Photo credit: Zurn Industries]
Image Credit: Image #1: Zurn Industries
Making a connection with Uponor's ProPEX components begins with slipping a plastic ring over the end of the tubing and then using a tool to expand the diameter of the tubing and ring. [Photo credit: Uponor]
Image Credit: Images #2 and #3: Uponor
After expansion, the tubing can be slipped over the end of a fitting or connector. The PEX quickly tightens around the fitting as the plastic tries to go back to its original diameter. [Photo credit: Uponor] Polypropylene pipe is inert, doesn’t react with chemicals, and withstands high pressure and temperatures. Connections are heat-fused. [Photo credit: Peter Yost]
Image Credit: Image #4: Peter Yost

Building his “forever house,” Dean Sandbo is mulling what type of tubing to use for his plumbing supply lines. He has narrowed the choice to one of two types of cross-linked polyethylene (PEX): PEX-A or PEX-B.

Key issues, Sandbo notes in his Q&A post at GBA, are how long the tubing will last, and whether there are safety concerns — that is, will the PEX tubing leach chemicals into his drinking water?

“I am on a well,” he writes. “Any input as to the longevity and safety of these two different types of pipes?”

Although that’s where the discussion starts, GBA readers quickly turn to another potential issue: What’s the best way of achieving a leak-free connection between tubing and fittings?

That’s the topic for this Q&A Spotlight.

Characteristics vary by type

There are actually three types of PEX, as a reference article supplied by GBA senior editor Martin Holladay explains (see the “Related articles” sidebar below). Types A, B, and C are manufactured differently, which affects characteristics such as flexibility, resistance to chlorine and oxidation, coil memory, and cost. The lettered designations aren’t grades, just references to the manufacturing process.

For Richard McGrath, PEX-A is at the top of the heap. “PEX-A is produced with a better manufacturing process than PEX-B as the crosslinking takes place during the extrusion process,” McGrath writes. “PEX-A products usually achieve an 85% crosslinking while PEX-B products average a 65-70%.”

PEX-A is more resistant to the chemicals commonly found in plumbing and heating systems than what it has replaced, he adds, and long-term testing by Uponor, one of the manufacturers of PEX-A, is very encouraging. The company holds an unofficial record for resisting high temperature and pressure, McGrath says, holding up to 175 pounds per square inch and 203°F between 1973 and 2009 — a stretch of 36 years.

“There is not another manufacturer that can make that claim,” he says.

Dealing with chlorine and chemical odor

Sandbo’s water source is a well, and well water is not typically chlorinated. That, says Nate G, removes one potential source of worry with PEX tubing.

“PEX in a ‘forever house’ … should be downstream of a water filtration system that removes chlorine,” Nate writes. “The reason is that chlorine eventually oxidizes and embrittles the pipe over time as the sacrificial anti-oxidizing agents are, well, sacrificed. With no chlorine in the water, this risk disappears. You also want high-quality low-zinc fittings. Don’t cheap out.”

Charlie Sullivan raises another issue: the unwelcome chemical taste that PEX tubing added to the water in his house.

“I’ll put in a vote for PEX-B,” Sullivan says. “I got my kitchen sink changed over from lead-soldered copper to Uponor PEX-A about a year and a half ago, and I found the taste terrible in the first few months — a strong plastic taste. I still flush the pipe before drawing a gallon of drinking water to save in a pitcher, even though I probably don’t need to. I haven’t done a controlled comparison to PEX-B, but given the comparison Martin linked to, I’d expect it to be significantly better in that regard.”

Comparing methods for connecting tubing and fittings

PEX is often connected to a fitting with a metal band that is tightened with a dedicated crimping tool. The pressure of the ring is designed to permanently and reliably seal the connection against leaks. The crimping rings are made from stainless steel, copper, or brass.

Uponor, however, uses a different type of connection. As demonstrated in this video, a plastic ring is fitted over the end of the tubing, and then an expansion tool is used to enlarge the tubing so it can fit over the end of the fitting. Very shortly after the two parts are brought together, the PEX tries to return to its original shape and as it does it tightens itself around the end of the fitting (see Images #2 and #3, below).

The tubing, says McGrath, is always tightening around the fitting, unlike with a crimped connection in which the tubing is pushing back against the crimping ring and trying to loosen.

“You cannot crimp Uponor PEX,” McGrath says. “A few years ago I was called to a group of modular homes to determine why the Uponor piping was leaking. Long story short, it was not the tubing leaking; the manufacturer of the home thought it would be OK to save on some fittings and used crimp rings and fittings made for other pipe, which are much smaller in diameter.

“PEX always wants to get back to its original size and form (due to its ‘memory’),” he continues. “If you use other than Uponor fittings and crimp it, it will leak, and there will be no warranty for you.”

Uponor frequently gets calls from plumbers who grow “argumentative” when told they can’t use crimping rings the plumbers already have on their trucks, McGrath says.

“Those folks are always told that you can use them but there will be no warranty coverage,” he says. “What does that tell you? It clearly tells me that you cannot do it and expect any sort of system integrity. Uponor does not make a crimp ring fitting nor will a crimp ring fit over Uponor tubing when a Uponor fitting is used.”

Mixing and matching doesn’t work

McGrath also warns against trying to use Uponor fittings with PEX-B tubing, or using incompatible fittings with PEX-A tubing made by Uponor or someone else.

“Uponor’s fittings with PEX-B is quite entertaining,” he says. “One would have to expand the PEX-B and you can, but the tubing will probably eventually leak because the molecular linking is of such a low percentage and, again, why would one do it?”

Results are equally disappointing when improperly sized fittings are used on Uponor’s or another brand of PEX-A, he continues.

“The fact that PEX-B and C use a crimp shows their inferiority since they are warranted to not leak all the while the product should be attempting to reach its original dimension,” he says. “Remember, this tubing has memory. Turns out that PEX-B and C have less memory, apparently, since they are willing to stay in the constrained size, whereas the PEX-A products will push out against the crimp ring, whether stainless steel or copper, and a leak path will form every time.”

Actually, there are alternatives

Rick Van Handel doesn’t argue the quality of the Uponor fitting system. But, he says, that has more to do with its unrestricted flow rate than anything.

“Whereas barbed fittings are placed inside the tubing, the already smaller inside diameter of PEX (compared to copper) becomes even smaller with these fittings,” he says. “As you know, the Uponor expansion fittings are full flow. However, by your logic, wouldn’t the PEX-A, which was expanded over the barb fitting, want to return to its original size and therefore tighten itself onto the barbed fitting in the same manner it would on an expanded fitting?

“I’ve used a lot of PEX-A with stainless cinch clamps on barbed fittings and I’ve never had one leak,” Van Handel continues. “I’ve hydro-tested these to 200 psi with no issues. Also, many people use the same combination for compressed air, which is even harder to seal, with no issues.”

Despite McGrath’s protestations, Van Handel says he’s had excellent luck with Uponor tubing and brass fittings.

“Personally, I’ve used mostly Nibco brass fittings and I use only Uponor tubing,” Van Handel says. “I haven’t had any leaks. That being said, I haven’t seen a rough-in my area with anything other than PEX-A and barbed fittings and stainless cinch clamps in a few years. It’s what almost all plumbers have gravitated towards in residential installs. In some commercial applications I still see expansion style fittings used or ProPress.

“I still agree with you that expansion fittings are likely superior, but to say that cinch clamps will certainly leak is a gross exaggeration,” he adds. “There are millions of these connections in place that are not leaking.”

Malcolm Taylor agrees. “For at least a decade, almost every building in British Columbia has been plumbed with PEX and crimp rings,” he says. “I’ve plumbed a half-dozen that way myself and have never had a leak.”

Our expert’s opinion

Here’s how GBA technical director Peter Yost sees it:

I think you can collect just about as many opinions and recommendations on PEX tubing and fittings as there are types of tubing and fittings. When I asked around, I could not come up with a clear “winner” for either.

So, let me add these two options to consider:

Aquatherm polypropylene pipe. It’s inert, doesn’t react with chemicals, and withstands high pressure and temperatures, and the pipes are heat-fused — so the fitting is thicker and stronger than the base pipe. If you are looking for “forever” pipe — and are willing to pay for it — this is the way to go. I have seen this in many commercial buildings of late. When I ask, “Why polypropylene?”, the response is: it’s forever pipe, and can handle the widest range of temperatures and stuff dissolved in the water. (See Image #4, below.)

Legend HyperPure pipe. A newer and therefore less proven candidate for those interested in a 100% recyclable alternative to PEX, this is a bi-modal polyethylene raised temperature (PE-RT) tubing. The resin for this tubing comes from Dow, and it’s called bi-modal because there are both high-molecular weight elements for strength and low-molecular weight elements for flexibility. Neither Legend nor Dow are exactly newcomers to piping and chemical formulations respectively, so while this piping solution may be less proven, it’s not the type of “high-risk” product we might associate with lesser-known start-up companies.


  1. Charlie Sullivan | | #1

    Polypropylene is great as far as taste and is also one of the better plastics as far as environmental impact of manufacturing. The downside is that, as far as I know, there's no way to do any work on it without a special heat welding system. Few plumbers in the US have those systems. I hope that will change, but for now I'd be hesitant to install that system unless there are at least two plumbers in your area who have good reputations and have the tools to work on it.

    Thanks for pointing out the Legend Hyperpure alternative. It would be interesting to see some third-party reporting about it.

  2. Steve Knapp CZ 3A Georgia | | #2

    What about push-to-connect
    I had a plumber work on my system recently, and he used Sharkbite push-to-connect fittings to change around some of the pex lines. Any concerns about the reliability of these pieces?

  3. Chris B | | #3

    The heat welding systems for PP aren't terribly expensive for residential pipe sizes (<2"), around $1k if I recall correctly. You can easily drop $2-3K on battery powered expanders / crimpers for Pex.

    The real downside (other than cost) is that it requires some additional planning for fittings and connections, and can't be used in a small diameter home-run system like pex can. So if you don't like waiting for hot water, you're back to a circulation loop.

    I REALLY don't trust sharkbite fittings. They're expensive, and the seal there relies entirely on a rubber washer that is likely to wear out much quicker than the PEX, and if we're already worried about the PEX longevity...Particularly w/ chlorinated water, I don't let them in the houses I work on.

  4. Nick Welch | | #4

    Uponor fittings are not
    Uponor fittings are not "unrestricted" or "full flow". Not even very close, either. A quick look at the specs will confirm this. They're just *less* restricted than typical PEX fittings.

    Inner diameters for 1/2 nominal products:

    Uponor PEX tubing: 0.475"
    Uponor fitting: 0.378"
    Standard PEX fitting: 0.350"


    You can also see it clearly if you have physical access -- the fittings are clearly smaller on the inside than the tubing.

  5. Malcolm Taylor | | #5

    Reply to Steve
    The main downside of Sharkbite fittings is their price. Most of the builders I know are comfortable using them in locations where they are exposed but are still reticent to bury them in walls. There is no reason to doubt their integrity, but a lot of us would rather wait and see what their long term reliability is. Most other fittings that rely on rubber gaskets for their seal are fixtures, like faucets or hose bibs, where the consequences aren't as large if they do fail.

  6. Skip Harris | | #6

    Mixed plumbing?
    If chemicals commonly leach from the PEX, why not use polypro for the common sources of drinking water and use PEX for the rest, especially home-run hot water?

  7. Charlie Sullivan | | #7

    Dustin's idea
    Dustin, I think that's a great idea.

  8. Chris B | | #8

    Mixed plubing
    We've looked at that on a couple houses, but in both cases the owner's opted for either full PP or full PEX. The reason is that one of the speculative downsides of PEX is a shorter service if you're paying to do a good chunk of the system in PP (including the line from the street), you might as well go whole hog and get "forever pipe" everywhere.

    I could see doing it in a very large house, though.

  9. Malcolm Taylor | | #9

    Mixed plumbing
    Chemicals added to a plumbing system (as when you drip chlorinate) are considered to be fully dispersed after 4 diameters of pipe length. Is there any research that suggests that chemicals leaching from pex pipes would stay isolated within what is a common, open water supply?

    We know contaminates that enter the pressurized water supply of a house can affect the municipal system it is attached to. If there are chemicals leaching from the pex, they are probably going to similarly end up present in all the house's water.

  10. Steve Knapp CZ 3A Georgia | | #10

    Thanks, Malcolm.
    I won't worry about changing out the Sharkbites then. But after reading this thread, I think I will reinstall my wholehouse water filter.

  11. M S | | #11

    Uponor fittings
    The question remains, which isn't necessarily answered in this article, does one risk using a fitting system other than Uponor, if by doing so you would likely have no warranty coverage. What Richard McGrath lays out seems pretty straight forward. Plumbers use other fittings, WHICH WILL WORK, however, if plumber/consumer want the manufacturer to honor a warranty to claim, they better have used the Uponor fittings.

    Seems like a no brainer to use them. Am I wrong?

  12. User avater GBA Editor
    Martin Holladay | | #12

    Response to MS
    If I understand Richard McGrath correctly, he is a big fan of Uponor tubing. That's fine -- lots of people have favorite brands. If you are using Uponor tubing, you need to use Uponor fittings. That's as expected.

    If you choose a different brand of tubing -- say, Nibco tubing -- then you use Nibco fittings. Again, no surprise.

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