With increasingly larger portion of contractors and homeowners turning away from copper and CPVC and switching to PEX, we’re inevitably facing the reality that PEX is not a final solution for the plumbing industry, and like its predecessors and competitors, has its own ups and downs. The good news is that a PEX system can be made to last beyond the 20-25 standard warranty and perform as needed when properly understood and installed.
Having been in the PEX industry for many years, we’ve heard it all – the PEX-A vs PEX-B debates, PEX vs. copper vs. CPVC, leaks, bursts, kinks and you name it.
While a reader may find that our share of experience is similar to that of others, we’ll try to provide not only a description of the common and not-so-common problems, but also the steps to prevent and remedy them where possible.
Before we proceed, we ask the reader to keep the following 3 things in mind:
1. PEX had its issues. And so did copper and CPVC. Anyone with a prejudice towards one type or brand of PEX and fondness of another should know that not a single major PEX pipe/fitting system used in the US has been problem free. Here are some examples (7):
PEX-A (Uponor/Wirsbo and Rehau): dezincification of fittings and chemical leaching/odor (AquaPEX only)
PEX-B (Zurn & Viega): dezincification of fittings
PEX-C (Nibco/CPI/DuraPEX): cracked, leaking pipes
PEX-AL-PEX (Kitec/IPEX): dezincification of fittings
There are probably others, less known names which are not on the list, but we believe the general idea is clear. Our purpose is not to scare way the reader nor to denounce these brands and companies, but merely to convey the general message. Majority of these companies have now switched over to DZR (DeZincification Resistant) brass or offer poly PEX fittings which are not subject to corrosion. A few have withdrawn from the residential market. As for Nibco, the pipe issue seems to be fundamental and according to out knowledge, the class-action lawsuit process is ongoing (as of December, 2015). Little is known about Kitec other than the case has been settled and the claim funds allotted.
Note that in all of the above cases (except NIBCO and AquaPEX), the issue was with the connections (read fittings), not the pipe itself. This important fact is missed by many PEX critics (and proponents of copper, CPVC or otherwise). Pinhole leaks in copper pipes and cracking of CPVC pipe happened and is still happening to day.
2. Water quality matters. A LOT. Factors such as pH level, chlorination and others have a direct effect on the life span and reliability of the system – including both PEX tubing and fittings. We’ve covered some of this here (PEX vs. Copper). A PB (polybutylene) pipe system, commonly installed decades ago and now accepted countrywide as “defective” had lasted only a few years in some cases, while in others exceeded the 20-25 year lifespan with no major issues. Why the difference? Water quality.
3. Experience makes a difference. With consistent local water quality, an experienced installer has the hands-on knowledge of what works best and what should be left alone in your particular area, whether it be PEX, copper or otherwise.
On the other hand, an unskilled contractor, not the manufacturer, may be at fault for improper installation and subsequent system failure. There are innumerable examples of such cases, many of which are publicly available.
With the above said, here is the list:
When water leaks from a PEX connection, it is generally caused by one of the following:
1. DeZincification – occurs with certain water chemistry, causing selective leaching of zinc from brass alloy and resulting in weakening of the fitting and leakages. To counter this problem, most PEX companies have already opted for a dezincification-resistant brass for their fittings. PPSU (poly alloy) PEX fittings can replace brass since they are not subject to this process and are widely available. Another method would be to use a “home-run” type system with continuous PEX pipe runs from a main manifold to the plumbing fixture, without any fittings or connections behind the walls. While this does not entirely exclude the possibility of dezincification of manifold and supply stop valves, it presents a safer alternative with better means of early problem detection and repair.
2. Push Fittings (Push to connect) – we’ve covered the issues with leaking push fittings here.
3. Tool was not calibrated properly – when using crimp or clamp/cinch methods, the tool should be calibrated prior to starting an installation and should be periodically checked by those who use it on a regular basis.
4. Failure to properly pressure test a system - may not only result in leakages but require removing of entire walls/floors, fixtures and other costly repairs. Pressure testing requirements may vary by area and we’ve covered some of the basics here.
It is true that due to the flexible nature of PEX, it is more burst-resistant than copper. Yet in low temperatures, if water completely freezes in the pipes, all types of PEX may burst.
Tested and proven solutions:
1. Drain the entire plumbing system when winterizing a summer home or a house where plumbing is not used in winter.
2. Insulate the pipes installed inside the outside walls with closed-cell, split type pipe foam insulation. U.S. DOE recommends (6) pipe insulation with a minimum of 3.0 R-value (~ 3/8” thick insulation walls). Select localities recommend R-value of 4.0 and above (~ 5/8” walls).
3. Install PEX pipe away from outside walls whenever possible. Not only will this greatly reduce the chances of freezing, but will help to save on insulation and hot water bills.
4. Bury PEX below the ground frost line if installing it under the ground outside (such as for outdoor wood boilers, furnaces, main/service lines, etc.). Several manufacturers in the U.S. offer pre-insulated PEX pipe encased in a larger diameter corrugated pipe, ready for installation in a trench.
5. Use hot water recirculation system without a dedicated return line to maintain a constant hot water temperature in pipes and at the fixture. Such system will also help to eliminate flushing lukewarm water down the drain while waiting for hot water to arrive from the water heater. Model such as Grundfos UP15-10SU7P/TLC (part# 595916) uses cold water line as a return line to circulate the water, therefore effectively protecting both hot and cold pipes against freezing. Just make sure your PEX pipe is rated for continuous recirculation (ASTM F2023). Everhot non-barrier PEX is among the few pipe brands which meet this standard.
6. Keep PEX away from sunlight. Like most other plastics, PEX will become brittle if exposed to sunlight for too long and may crack under pressure. Typical exposure limit is ~30 days. Some manufacturers offer UV-stabilized PEX pipe with added inhibitors which may extend exposure time to around 6 months, but there are no permanent solutions we know of.
7. Give it some slack. Since PEX will expand and contract 1-2.5” per 100ft of length with every 10°F changes in water temperature, it should not be pulled tight during the installation. In case of 60F temperature rise, 100ft may elongate as much as 15”. Use tube talons and pipe clamps which allow for movement of the pipe without damaging it and make expansion loops on long runs of pipe which will carry hot water. Failure to properly secure the PEX pipe will overstress it and may cause mechanical damage and even ruptures.
Chemical taste and/or odor in PEX plumbing systems may be caused by (2) main factors:
1. Leaching of chemicals due to water quality. This is probably the most important issue of all and it deserves a treatise of itself, but for the purposes of this text, we will provide a shortened summary and references for further independent research. We used data from (4) independent, publicly available studies on or related to contaminant diffusion in PEX systems (1), (2), (3), (4) and one in-house testing of Everhot PEX.
Findings in the primary study (1) point out that:
1. Level of dissolved contaminants in water directly affected by chlorine concentration.
2. In identical conditions, less dense pipe (PEX-A, made from MDPE) leached much more contaminants into water (in some cases up to 200% more) than the higher density pipe (PEX-B, made from HDPE).
In-house testing revealed OIT (“oxidation induction time”, or how quickly the pipe degrades/becomes brittle) of PEX-A tubing sample to be 460% faster than that of PEX-B (Everhot PEX and another sample) at 410°F. In other words, PEX-A degraded over 5 times faster than PEX-B and as a result, leaches excessively more contaminants. While 410°F temperature is beyond the maximum rated temperature for PEX, it should convey the message clearly.
Another study (4) indicates that exposure to water over-saturated with all (3) common disinfectants – chlorine, chloramine and chlorine dioxide significantly affected stability of PEX pipe during testing, making the pipe more brittle and prone to cracking. This is another important reason to assure that your PEX plumbing pipe meets ASTM F2023 standard for resistance of PEX to chlorine. There exist opinions that F2023 is not comprehensive since it does not include chloramine and chlorine dioxide testing, but the study evidence suggests it is not necessary since all (3) disinfectants affect the pipe in a similar manner. PEX pipe which meets ASTM F2023 has a life expectancy of about 50 years (3).
Combined together, these reports clearly suggest that the primary reason for leaching of chemical from PEX is over-chlorination of water. Conclusively, PEX is therefore, best suited for low- and non-chlorinated plumbing systems.
Possible solutions and preventative measures:
While this information may come as a surprise for some, we also want to note that copper pipes are also subject to degradation and contaminant leaching, causing increased water toxicity (5). Conclusively, in order to make a safer and healthier choice, water quality should be tested prior to selecting either PEX or copper and an informed decision made based on numbers, not mere opinions or personal preferences.
2. Odor or aftertaste caused by improper storage, installation or from municipal or groundwater (well water) water contamination. PEX, like many other plastics (i.e. polypropylene jugs used for milk and juice) may absorb odors. If improperly stored or installed next to a source of odor, PEX may transfer it (albeit, in small amounts) to water, resulting in unpleasant smell or aftertaste.
A number of residents living in areas with increased industrial activities (drilling, manufacturing) have also reported gasoline-like or chemical odor/taste in water. In both cases, these issues do not originate in PEX plumbing systems.
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