Corrugated Stainless Steel Tubing, or CSST, is one of those things that most people don't even think about until they hear about it at their home inspection. Many homes built since the 1990s have this product, and as with most new product introductions, there is a learning curve.
Yellow CSST gas lines are connected to a black pipe manifold.
If your home is newer or if you have added any new appliances, the contractor probably used CSST. CSST is the flexible yellow gas line that you may see running to your furnace, water heater, or other gas-fired appliances in your home.
Grounding versus bonding
Even after several years, there is still confusion in the real estate and home inspection industries regarding bonding. Grounding and bonding look very similar but are very different.
Grounding ensures an electrical fault has a pathway back to the utility’s transformer. Grounding is designed to prevent harm or damage to people and property. A fault is when electricity flows on a conductor where it should not be, such as a short circuit.
Bonding is a permanent connection to metal objects such as metal appliances, pipes, metal framing, etc. Bonding effectively connects these features to your home’s grounding system. Bonding ensures continuity if something metal becomes accidentally energized. Bonding also protects against energized potential due to a nearby lightning strike.
What is CSST?
Corrugated stainless steel tubing, commonly known as CSST, is a flexible, semi-rigid, thin-walled tube typically covered in a yellow jacket. Newer products have a black jacketing and the ability to dissipate energy through the jacketing material. CSST should be distinct from a flexible gas connector, which is also corrugated but painted yellow.
CSST from the wall to the black pipe. Gas appliance
connector from the black pipe to the water heater.
CSST is designed to be bent to shape to meet installation requirements. After installation, CSST should remain stationary. Think furnaces, boilers, water heaters, cooktops, etc. CSST should not be exposed to impact, vibration, or repeated movement.
There are only a few specifics in the building codes with respect to CSST. This can sometimes create confusion between the trades, as the plumber and electrician need to have clearly defined codes to follow. Usually, what you will find in the codes refers to the manufacturer’s instructions. Each manufacturer has produced documentation with specific installation requirements. The good thing is that these requirements are similar from manufacturer to manufacturer.
CSST bonding
When a home inspector sees CSST at a home inspection, the first thing they look for is to see if it has been adequately bonded. Bonding means the CSST has a mechanism to ensure it has the same electrical potential as everything else. There is a risk of damage to the CSST if it is not bonded to the current standards. If there is a lightning strike, either directly to the structure or nearby, there can be arching between the CSST and adjacent metal surfaces, which may result in a gas leak.
After initial use in the late 1990s and early 2000s, manufacturers started implementing bonding requirements in the 2006 timeframe. As home inspectors, we started calling out the lack of proper bonding as these requirements crept into the building codes.
Does existing CSST need to be bonded?
When something was installed before existing codes, it is typically “grandfathered.” Grandfathered means that it is still compliant if installed under a previous code.
As a home inspector, we do not focus on code compliance. Codes change about every three years. We focus on safety. Current residential construction standards may deem something unsafe, even if installed correctly according to a previous code. Per our Standard of Practice, it is the home inspector's job to document and report safety issues.
Over time, safety issues may arise, so requirements may be updated to improve product safety and performance. Manufacturers change and improve requirements for the installation of their products. So, even if the initial installation was done correctly and according to the codes at the time, we will recommend a safety upgrade, as we know there is an unacceptable fire risk without proper bonding in the event of a nearby lightning strike.
Bonding locations
Initially, the bonding was required to be done where the CSST originated. If it were at the gas meter, the bonding would be done at that location. If it were at a manifold in the basement, the bonding would be done at that location. Over time, it was determined that the bonding clamp attachment may be at any point in the gas piping system as long as they are placed per requirements.
Proper bonding examples
Proper bonding requires installing a separate bonding wire with an approved bonding clamp. The bonding clamp shall be connected directly to the ridged piping or to one of the CSST nuts. Bonding is required even if there is just a short section of CSST.
Bonding clamp and wire attached to the CSST nut.
Older style yellow-jacketed CSST.
Bonding clamp and wire attached to a rigid gas pipe.
Newer style black-jacketed CSST.
Initially, when bonding CSST, it was required that the other end of the bonding wire be routed back to the electrical panel. The newer fuel gas codes now allow for the CSST to be bonded anywhere on the grounding electrode of the electrical service grounding system. The bonding wire can be attached to a grounding rod or any metallic water piping coming into the home, basically anywhere on the service grounding electrode system. Current requirements can be found in Section 310.2 of the Minnesota Fuel Service Gas Code. The intersystem bonding terminal is the one place you cannot bond to, as it is specifically designed for low-voltage communications systems such as phone lines, satellite systems, and internet/cable television.
Insulation or air gap?
In addition to bonding, CSST should not contact any adjacent metal surfaces. In early installations, brackets were commonly used to attach CSST to furnace ducts or the side of a water heater. Additionally, our home inspectors find installations where the CSST is in direct contact with the sheet metal edge of a gas fireplace chassis.
CSST in contact with the metal chassis edge at a fireplace enclosure.
Manufacturers require an air gap or other means to insulate CSST, such as brackets that hold the CSST away from metal. If CSST is touching metal, there is a risk of arching in the event of a lightning strike. The arching may result in a hole in the CSST, which will cause a gas leak and/or fire. Installing foam tubing around the CSST or running it through a PVC tube are also ways to create separation.
A foam tube is used to protect the CSST installed between the furnace ducts.
A PVC pipe is used to protect the CSST at the water heater.
How can you know if you have CSST in your home?
Look for flexible tubing with a yellow or black jacket that covers the ridges. CSST either has a yellow jacket or a black jacket. This material is not to be confused with an appliance connector, which might have a yellow coating that follows the contours of the ridges. The photo below shows the two different materials.
Photo by Rueben Saltzman
Summary
If your home has CSST, you should ensure it is bonded and has proper clearances from metal surfaces by today’s standards. Codes change for performance and safety over time. Even if your CSST met the code at the time of the installation, we have learned that there are some reasonable safety measures added that will help to protect you and your family.
When in doubt concerning your CSST installation, call a qualified professional. They will make sure that the CSST is installed following the manufacturer's instructions as well as the latest building code.
At HomePro Inspections, our home inspectors are trained to inspect all areas of the home. Proper installation of CSST to meet the latest requirements is an important safety issue. Any issues found are documented in your home inspection report and recommended for resolution by a qualified professional.
Visit our website to learn more or to schedule your home inspection in the Rochester, Owatonna, and Faribault, MN areas. You can contact us today at (507) 202-8942 or utilize our online “Schedule Now” feature to set up an appointment.