The opinions expressed in this article are those of the author only and do not necessarily reflect the opinions or views of ASHI. The information contained in the article is general and readers should always independently verify for accuracy, completeness and reliability.
Although corrugated stainless steel tubing gas piping systems (also known as CSST) have been installed for over 30 years, this variety of gas piping is still relatively unknown to both homeowners and home inspectors. While all home inspectors should know what CSST is, some may not be familiar with it beyond a rudimentary understanding.
All gas piping systems, regardless of the piping material, are installed in accordance with the local fuel gas or residential code in effect. CSST systems are also installed in accordance with the manufacturer’s installation instructions, which oftentimes conflicts with the local code. For example, electrical bonding code requirements have been revised four times over the past 12 years, and yet the manufacturer’s instructions have remained basically unchanged throughout that same period. The codes in many states lag far behind the updated model codes for years, causing additional confusion. To that end, it is important for home inspectors to understand the common and best practices associated with CSST, and how to recognize and note them on their inspection report.
The fuel gas code recognizes four different piping materials for the distribution of either natural or liquefied petroleum (LP) gas. These materials include steel pipe, copper pipe/tubing, CSST and polyethylene pipe (for underground only). The code also allows different piping materials to be combined in a given piping system. The installer makes the choice of piping, and there is no code preference given to one material over another. The fuel gas code has general requirements for routing, supporting, sizing, connecting, protecting and testing of all gas piping systems.
What the home inspector must learn is how to identify those requirements that are beyond his or her responsibility from those that should be reported. For example, the code deals with mechanical protection of CSST in areas where it will be concealed after completion of construction. The home inspector cannot possibly inspect for mechanical protection if neither the tubing run nor the striker plate can be seen without removing permanent building structure. Much of the gas piping system is typically hidden behind walls, between floors or underground, which prevents any examination or identification or both.
Sizing of gas piping is a code requirement affecting many aspects of the piping system layout and choice of accessories. The home inspector has no way of confirming any of the choices made by the plumber when sizing the piping system. Often, gas appliances are upgraded with bigger units, which can affect pipe sizing or create a problem in the appliance operation. Unless there is an obvious and detectable operational problem with an appliance or regulator, the confirmation of proper pipe sizing is considered outside the responsibility of the home inspector. So, what is left to inspect? Well, it turns out that there are some important aspects of the CSST gas piping system that need to be inspected and reported.
There are five brands of CSST commercially available in the United States, and two kinds of protective jackets. The more traditional CSST jacket is yellow and made of polyethylene that provides general protection against weather and household chemicals. The more advanced CSST jacket is black and is electrically conductive to protect against arcing as well as weather and chemicals.
All brands of CSST are tested and certified to the same national standard, although each brand has a unique fitting design. All CSST products are installed in accordance with the same industry guidelines and local codes. The manufacturer’s installation instructions, which must be in accordance with the national model codes, are available in print or online.
As shown in Figure 1, identification markings are required and provide useful information to the code official, the installer, the homeowner and the home inspector. The markings are repeated every 2 feet along the tubing and include the following: trade name/manufacturer, model/part number, listing standard, tubing size, pressure rating, listing organizations, the manufacturing date and the term “gas.” Any CSST without these markings indicates that a non-listed product has been installed in violation of the code, and this should be noted on the inspector’s report.
The home inspector should take note of at least four important items:
- Manufacturer/Trade name
- Tubing size
- Jacket color
- Manufactured date
CSST can be installed throughout a house through a wide variety of pathways, including wall cavities, attic, basement and crawl spaces, underground, above ground, between floors and in open exposed surface areas of the structure. While much of the CSST is typically installed in concealed locations, there can and will be locations where it will be visible for inspection.
Common locations where CSST can be examined include meter connections, appliance connections, tubing runs in unfinished basements, crawl spaces and attics, garages and certain tubing runs outdoors above ground. At these locations, it is important to inspect the manner and degree of support given to the tubing runs. Metal hangers are currently required, but plastic clips have been permitted in the past. In addition, appliance connections can be inspected for compliance with critical code requirements.
Appliance connection requirements depend on the type and location of the appliance. Fixed appliance connections normally include a shut-off valve, sediment trap and a pipe nipple/union combination or a flexible appliance connector. Flexible connectors are not the same as CSST, although (to the untrained eye) the two products have a similar external appearance. These two products are manufactured based on different standards and different purposes, and they have different markings. Moveable appliances are connected to the piping system using a flexible appliance connector located downstream of the appliance shut-off valve (which must be securely fastened to the building structure). Figure 2 A and B shows an external comparison of a flexible connector and CSST.
Many CSST systems are designed to operate at pressures up to 2 pounds per square inch (psi), compared with the traditional 7 inches of water column pressure. The use of 2 psi requires the installation of a line pressure regulator somewhere in the house between the gas meter and the appliances to permit the redistribution of the fuel gas to individual supply lines. The line pressure regulator is often associated with a distribution manifold, which must be located in an accessible location for inspection and maintenance. The orientation of the regulator is also a checklist item for the inspector to ensure proper functioning.
This arrangement is known as a gas load center (as shown in Figure 3) and must include the following components:
- Line pressure regulator with vent limiter or a vent line to the outside
- Upstream shut-off valve
- Upstream drip leg and pressure measurement port
- Pipe union
- Downstream drip leg or pressure measurement port
Typically, these gas load centers are located in garages, basements, attics and mechanical rooms. In some cases, each appliance in the piping system could have its own line pressure regulator installed near the piping connection to the appliance.
Electrical protection of CSST from arcing due to lightning strikes is both a code and manufacturer requirement. Fuel gas code requirements (NFPA 54, ICC and IAPMO), beginning with the 2009 editions, mandate the installation of extra bonding for all CSST piping systems. This bonding is over and above the bonding requirements for gas piping found in the National Electrical Code (Section 250). CSST bonding requires a single clamp on the piping system that connects to the electrical grounding system with at least a #6 copper conductor (as shown in Figure 4), and an appropriate clamp to one of the permitted connections to the grounding system. The clamp must not be installed on the CSST jacket, and it must have a metal-to-metal interface with the underlying piping. This requires that any paint or coating on the piping be removed before attaching the clamp. However, new CSST jacket technology, other standard lightning protection methods or a combination can also be utilized. The extra arcing protection can be provided in at least one of the following three ways:
- Bonding the CSST to the electrical grounding system with a #6 copper conductor
- Installation of arc-resistant black CSST with conductive jacket
- Installation of a lightning protection system per UL96/96A or NFPA 780
Code compliance on CSST bonding varies widely around the United States where different adopted codes, different editions of codes and state amendments have made enforcement difficult to predict. The responsibility of the home inspector has been defined and limited to identification of the CSST installed. The inspector is not required to make any determination of whether bonding is required, if bonding has been performed or if the bonding has been performed correctly or effectively. However, the home inspector should consider stating in their final inspection report what they can identify regarding the CSST installation as well as this statement, which is required in a few states (Oklahoma, Texas, California, Virginia and Maryland):
“Manufacturers believe the product is safer if properly bonded and grounded as required by the manufacturer’s installation instructions. Proper bonding and grounding of the product can only be determined by a licensed
For more information on bonding and electrical arcing, visit the following websites:
Home inspectors can contact the individual CSST manufacturer to ask site-specific questions on installations that do not comply with these general practices, or to get guidance on code interpretations affecting the piping system installation.
Robert Torbin, PE, has worked for over 35 years in the development of innovative fuel gas piping systems and related technologies. He has a BS in Mechanical Engineering from Northeastern University and an MS in Mechanical Engineering from WPI. He is a Registered Professional Engineer and serves as a member of several national standards committees, including the CSST ANSI LC-1 TSC, the CSA Manual Valve TSC, and press connections ANSI LC-4 TSC. He is a voting member of the NFPA 54 Technical Committee. He has authored or coauthored over 100 technical reports, journal articles and conference papers, including many on gas distribution research. He lectures to numerous gas industry organizations and plumbing, mechanical, electrical and fire inspector groups every year.