Understanding Material Limitations When Designing Plumbing for Hotels and Multi-family Residences

Plumbing engineers take pride in designing and specifying systems that provide the best experience for building owners and occupants. Yet, specifications that mix materials or are written so broadly that the contractor can make major design and material choices, fail to account for the significant differences that exist between commonly used materials such as CPVC and PEX. That can lead to issues that reduce plumbing system performance and reliability.  

Pressure and Sizing Differences 

It might surprise engineers to learn that more than half the plumbers who participated in a FlowGuard Gold CPVC plumbing quiz believed that fittings had no impact on water pressure. Engineers understand that fittings create pressure loss in all plumbing systems, with some fittings having a greater impact than others. But you can’t rely on contractors to account for these differences in the field, especially considering the magnitude of the difference in the internal diameter and the pressure drop between PEX and CPVC fittings.

The PEX fitting with the lowest pressure drop has a pressure drop roughly six times higher than the “equivalent” FlowGuard Gold CPVC fitting in a ½” 90⁰ elbow. Other types of PEX fittings create even higher pressure drops as shown in the table below. Unless pipe is upsized to compensate, pressure at fixtures could be compromised.  

Figure 1: Calculations for pressure drop of PEX and FlowGuard Gold CPVC ½” 90-degree elbows at three temperatures using the Plastics Piping Institute’s Plastic Pressure Pipe Design Calculator and manufacturer-published data.  

Another case where upsizing may be required when using PEX is hot water recirculating systems. PEX manufacturers and some model codes limit water velocities in PEX to 2 feet per second in hot water recirculating systems. That can dramatically reduce flow rates across the system and typically requires upsizing the piping to manage velocity while still providing adequate volume.

When engineers leave material selection and design fully in the hands of the awarded subcontractors, there is a significant risk that the installed system will end up being under-sized, resulting in inadequate water pressure, excessive velocity, or pre-mature failure of the system. Contractors who actively seek to avoid these issues, may end up oversizing the system, resulting in slow hot water delivery times and reduced water efficiency.  

Compatibility with Chlorinated Drinking Water

The biggest difference between PEX and FlowGuard Gold plumbing systems is the ability to handle chlorinated drinking water without degrading. FlowGuard Gold CPVC is a chlorinated compound developed for U.S. water systems, so it is immune to degradation from chlorinated drinking water. PEX is a polyolefin, similar to polybutylene and polypropylene, which is vulnerable to chlorine degradation that can lead to early failure. 

This issue led the Plastics Pipe Institute (PPI) to publish Technical Note 53: Guide to Chlorine Resistance Ratings of PEX Pipes and Tubing for Potable Water Applications. This note identifies some of the conditions that can accelerate chlorine degradation in PEX pipes, including the oxidation-reduction potential (ORP) of the water flowing through the pipes.  

Engineers don’t generally have access to data on the ORP of the water that will be flowing through the pipes of a building, so they can’t have confidence that PEX can handle local conditions. Even if they did have that data, municipalities can and do change their treatment practices regularly to adapt to the variety of factors that affect water quality. These changes can increase the water’s ORP – and the risk to PEX pipes. 

One such change is the switch from chlorine to chlorine dioxide as a secondary disinfectant. As shown in Figure 2, chlorine dioxide is a very strong disinfectant with the ability to exceed PEX’s ORP limits, even at relatively low levels. This development led the PPI to publish Technical Note 67: Chlorine Dioxide and Plastic Hot- and Cold-Water Plumbing Distribution Pipes. Based on published research, the PPI found that chlorine dioxide has the potential “to reduce the service life below normal expectations” of PEX and other plumbing systems. 

PEX manufacturers go even further in their published guidelines. Several leading manufacturers explicitly advise against the use of their products “as part of any potable-water distribution system in buildings where chlorine dioxide is used for secondary disinfection…” 

By contrast, FlowGuard Gold CPVC can be used in buildings where chlorine dioxide is used for secondary disinfection. TN 67 notes that “chlorine dioxide is not known to be aggressive to CPVC at elevated temperatures of 200°F (93°C) and below.” 

Figure 2: Chlorine dioxide, represented by the ◊ in the graph, drives ORP above PEX’s limit of 825 mV at relatively low dosages.  

Risks Related to PEX Water Incompatibility

Because these chlorine-related failures can take several years to develop, contractors rarely consider these factors when selecting materials in a design-build environment for hotels and multi-family buildings. However, as a plumbing engineer you are responsible for designing and specifying buildings that work, not just for the first few years after construction, but for the long-haul.

Building owners who experience these failures may not find relief in PEX product warranties. Many PEX warranties contain exclusions that effectively void the warranty as soon as chlorinated water flows through the pipe. Based on these exclusions, if a PEX system fails due to degradation caused by the water flowing through it, the warranty will not cover any damages or repairs.

In the worst cases, these PEX failures have led to legal action. There have been at least a dozen settled class-action lawsuits resulting from systemic PEX failures in recent years.  Last year, our team met with the operator of a group of hotels that were built in 2016 using PEX piping that started experiencing chlorine-related failures, eventually resulting in a complete re-pipe using FlowGuard Gold pipe and fittings. The involved parties were unable to comment for this piece as the project remains the subject of ongoing litigation.

By specifying FlowGuard Gold CPVC, engineers’ can future-proof their projects against these types of failures.  

Protecting Your Clients Reputation

Creating “or equal” specifications that give contractors the flexibility to select the plumbing system may seem like a good idea, but it increases risk for building owners when contractors choose materials that compromise performance and reliability. And developing specs that combine multiple materials ensures the system will only be as good as the weakest material. If you want to ensure you are delivering the best experience for building owners and occupants, download the specifications for PEX and FlowGuard Gold CPVC and do a side-by-side comparison.