The Plastic Plumbing Materials Selection Checklist

Plastic plumbing materials have dominated the new construction market for years. Yet, the key differences between the leading plastics systems, PEX and CPVC, are too often not considered during material selection. That makes it harder for contractors to choose the material that is right for their business and their customers. Here are four criteria that can improve material selection.

1.    Compatibility with Local Water Conditions

There are dozens of class action lawsuits that have exposed water compatibility issues with certain plumbing systems. These lawsuits involve the reaction of copper pipes to chloramines and PEX to chlorine.

In Technical Note 53, the Plastics Pipe Institute (PPI) lists an oxidation reduction potential (ORP) above 825mV as one of the factors that can accelerate chlorine degradation in PEX pipes. The ORP of drinking water is heavily influenced by the disinfectants used, including chlorine, chloramines and chlorine dioxide.

According to International Dioxcide, chlorine dioxide has a 2.6-times higher ORP over conventional chlorine. Higher ORP values generally mean better microbial control and reduced contamination risks so municipalities have an incentive to increase ORP rather than managing it to protect piping materials vulnerable to chlorine degradation. In addition, municipalities must regularly adapt their disinfection methods to changes in the distribution network or water quality. Contractors have no way of knowing what the treatment method or ORP of the water flowing through the pipes they are installing will be in the future. 

When chlorine dioxide is implemented for water treatment, the ORP of the water can easily exceed the 825mV limit for PEX piping. Responding to this concern, the PPI released Technical Note (TN) 67: Chlorine Dioxide and Plastic Hot- and Cold-Water Plumbing Distribution Pipes. According to TN 67, “the published results indicate that chlorine dioxide has the potential to reduce the service life of most plumbing distribution materials.” However, the report also found that “chlorine dioxide is not known to be aggressive to CPVC at elevated temperatures of 200°F (93°C) and below.”

While chlorine dioxide is still an emerging water treatment technology, analysis of occurrence data from the US EPA’s UCMR 5 January 2025 release shows that usage of chlorine dioxide has increased by at least 94% in the last five years with one-third of the data still to be collected.  

Material manufacturers don’t actively promote their water incompatibility issues for obvious reasons, but you can get a sense of them from the manufacturer’s warranty and other documentation. Some warranties may not include damage caused by chemicals in the water. In terms of chlorine dioxide, some PEX manufacturers recommend against the use of their materials as part of any system where chlorine dioxide is used as a secondary disinfectant. Unfortunately contractors have no control over what disinfectants will be used after the system is installed, making it difficult to take action based on this warning.

One way to protect the pipes you are installing today from premature failure due to incompatibility with local water conditions is to choose a material 100% immune to chlorine, chloramines and chlorine dioxide in drinking water. FlowGuard Gold and Corzan CPVC confidently stand behind decades of proven performance under chlorine-based water treatment methods.

2. Water Pressure and Flow

PEX and CPVC plumbing systems use different styles of fittings. With CPVC, the pipe is inserted into the fitting and solvent welded together, whereas with PEX the fitting is inserted into the pipe and the two pieces are mechanically joined using other components. This fundamental design difference has a direct impact on the pressure drop introduced by fittings. Even expansion PEX fittings have a much smaller internal diameter than a CPVC fitting and that results in a larger pressure drop. In a ½” 90-degree elbow, a PEX expansion fitting can create a pressure drop up to six times that of a CPVC fitting.

These larger pressure drops can make it necessary to oversize piping to compensate, particularly in fitting-intensive applications like luxury showers with body sprayers. The number of fittings required to balance the flow and pressure within and across the loops in these systems can require upsizing the loop piping and the branch line by one or two sizes when using PEX. CPVC does not typically require upsizing due to the lower pressure drop introduced by CPVC fittings.

3. Speed and Cost

Opinions vary among contractors about which plumbing system is easiest to work with and installs the fastest. However, in a time study conducted by the NAHB’s Home Innovation Research Labs, CPVC installed about 15% faster than PEX in trunk and branch configurations. PEX installed 10% faster than CPVC in mini-manifold systems, but those systems used more material. The added costs associated with the extra material in mini-manifold designs would likely offset the limited time savings.

CPVC’s installation speed may be attributed to the relative simplicity of the solvent welding process used to connect CPVC pipes and fittings. The solvent weld process also chemically fuses the fitting and pipe into a single piece of CPVC, which is the strongest part of the system. The strength of that bond enables CPVC to be used under slab, which can create further speed and cost savings in some situations.

CPVC may also offer lower material costs than PEX. In one  analysis of costs for a hypothetical project published by a PEX manufacturer, CPVC material costs were estimated to be half that of the PEX system.

4. Performance History 

It can take years for plumbing system reliability issues to surface as the industry found out in the early 1990s with polybutylene. American water disinfection practices are different than those used in other areas of the world, so materials that perform well in other regions may not deliver the same reliability when brought to the US. PEX was originally used in Europe. Since being introduced into the US, it has faced a number of legal claims alleging pipe failures. CPVC has been proven in American homes for more than 65 years and FlowGuard Gold CPVC is the most used brand of non-metallic pipes over that time. To review sample specifications for FlowGuard Gold CPVC, visit flowguardgold.com.

Jonathan Simon is the North American residential plumbing manager for Lubrizol Advanced Materials Inc., the parent company for FlowGuard Gold Pipe and Fittings.