CSST Gas Line: Bonding, Lightning and Inspection Concerns

We may earn commission from links on this page. Lead-form submissions are forwarded to local inspector partners. How we research and review.

Walk into the basement, attic or garage of many homes built or remodeled since the 1990s and you may see a yellow or black plastic-jacketed tube running to the furnace, water heater, range or fireplace. That is corrugated stainless steel tubing, usually called CSST. It is a legitimate, code-recognized gas piping material that installs faster than threaded black steel pipe. It also carries one well-documented concern: lightning. When nearby lightning energizes a home’s metal systems, thin-walled CSST can arc and develop a hole, and leaking gas can ignite. Manufacturers and fuel gas codes address that risk with bonding requirements, but older installations may not meet them. This guide explains what a CSST gas line is, how lightning damage happens, what bonding involves, how yellow and black jackets differ, what home inspectors can and cannot determine and what corrections typically cost. Gas and electrical work should be done only by licensed professionals.

Part of our Heating, Cooling & Ventilation guide — start there for the full picture →

What a CSST Gas Line Is

CSST is a thin-walled, flexible stainless steel tube with corrugations along its length, covered by a protective plastic jacket. It comes on reels and is bent by hand around framing, so a plumber or gas fitter can run long continuous lengths with few joints. Each brand uses its own proprietary fittings at the ends.

According to the American Society of Home Inspectors (ASHI), the fuel gas code recognizes four piping materials for natural gas or liquefied petroleum (propane) distribution: steel pipe, copper pipe or tubing, CSST and polyethylene pipe (for underground only). The code allows materials to be combined in one system and gives no preference to one over another. ASHI also notes that all brands of CSST are tested and certified to the same national standard, and that the tubing must carry identification markings repeated every 2 feet, including the trade name or manufacturer, the listing standard, tubing size, pressure rating and the word “gas.” ASHI advises inspectors that CSST without those markings indicates a non-listed product that should be noted in the report.

Where CSST is commonly found

• Runs from the meter into the house and through joist bays in basements and crawl spaces.
• Branch lines in attics feeding furnaces, rooftop units or gas fireplaces.
• Connections to ranges, dryers, water heaters, outdoor grills and fire pits.
• Gas load centers where a manifold splits one supply into several appliance lines.

ASHI notes that many CSST systems operate at up to 2 pounds per square inch (psi), compared with the traditional 7 inches of water column, and use a line pressure regulator, often at a manifold, that must remain accessible for inspection and maintenance.

CSST versus flexible appliance connectors

CSST is often confused with flexible appliance connectors, the short corrugated lines behind ranges and dryers. ASHI explains that they are built to different standards for different purposes. Appliance connectors are typically 1 to 6 feet long with factory-installed fittings on each end and often have visible, painted corrugations, while CSST is a sheathed distribution system. ASHI also flags uncoated brass-colored appliance connectors from the 1970s as a known gas leak hazard that inspectors should report. If a range is being replaced, our gas stove installation guide covers connectors and shutoff valves.

Lightning and CSST: How the Damage Happens

Lightning does not have to hit a house directly to cause trouble. A nearby strike can induce large voltages on wiring, cable lines, metal chimneys and gas piping. If two metal systems inside the house end up at very different voltages, electricity can jump, or arc, between them. With thick-walled steel pipe, an arc might leave a small pit. With thin-walled CSST, an arc can burn a pinhole through the tubing wall. Gas escaping at that point can be ignited by the same arc.

The consequences can be severe. The U.S. Fire Administration has highlighted a Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) investigation into two firefighter line-of-duty deaths in Howard County, Maryland, in 2018 and 2021. USFA reports that ATF determined the origin and cause of both fires to be lightning-induced arc failure of CSST, and that in both incidents the floor collapsed above the location of the CSST gas line while firefighters were working on the level above.

Colorado’s Front Range sees frequent summer thunderstorms, and homes on open ridgelines, in foothill neighborhoods or with tall metal chimneys may be more exposed. Lightning risk varies by location, but the question of whether a home’s CSST is properly protected is worth asking anywhere it is installed.

Bonding Requirements Explained

Bonding means connecting metal systems together with a conductor so they stay at the same electrical potential, which reduces the chance of a damaging arc between them. ASHI’s guidance for inspectors states that electrical protection of CSST from lightning-induced arcing is both a code and a manufacturer requirement, and that fuel gas codes (NFPA 54, ICC and IAPMO) beginning with their 2009 editions mandate extra bonding for CSST systems. According to ASHI, that bonding is over and above the general gas piping bonding found in the National Electrical Code.

As ASHI describes it, typical CSST bonding involves:

• A single listed clamp attached to the gas piping system, not to the CSST jacket itself, usually on a rigid steel pipe segment or brass fitting near where the gas enters the house.
• A metal-to-metal connection at the clamp, which means removing paint or coating from the pipe where the clamp attaches.
• A conductor of at least #6 copper running from that clamp to an approved point on the home’s electrical grounding system.

ASHI also notes that newer jacket technology, other standard lightning protection methods or a combination can be used to provide arcing protection, and that requirements have been revised several times while manufacturer instructions remained largely unchanged. Bonding length limits, clamp locations and acceptable grounding connection points depend on the manufacturer’s instructions and the code edition adopted locally. That is why a licensed electrician or gas professional, not a homeowner, should determine what a specific system needs. Our electrical grounding guide explains how the grounding electrode system works.

Bonding is not lightning protection for the whole house

CSST bonding reduces the risk of arcing at the gas piping. It does not make the house immune to lightning, and it does not protect electronics. A whole-house lightning protection system (air terminals, conductors and grounding) is a separate, specialized installation. Surge protection for the electrical panel is another separate layer, discussed in our whole-house surge protector guide.

Yellow vs Black Jacketed CSST

ASHI describes two kinds of CSST jackets. The traditional jacket is yellow polyethylene, which protects the tubing from weather and household chemicals. The newer black jacket is electrically conductive and designed to help protect against arcing as well as weather and chemicals. Several manufacturers sell black-jacketed, arc-resistant versions of their tubing. ASHI lists three ways the extra arcing protection can be provided: bonding the CSST to the electrical grounding system with a #6 copper conductor, installing arc-resistant black CSST with a conductive jacket, or installing a lightning protection system built to UL 96/96A or NFPA 780. Which option applies to a given installation depends on the manufacturer’s instructions and the locally adopted code.

A few cautions:

• Color alone is not proof. ASHI notes that CSST jackets also come in other colors, and appliance connectors can be yellow or black too. The printed markings on the jacket identify the product.
• Mixed systems exist. A home may have yellow CSST from the original build and black CSST added during a remodel. Each portion follows its own manufacturer’s instructions.
• Black jacket is not a reason to skip normal bonding. All metal gas piping is expected to be bonded under the electrical code. Check the specific product’s instructions for anything more.

Some homeowners with yellow CSST choose to replace it, particularly in exposed locations, but bonding an existing system to current manufacturer requirements is the more common correction.

Gas Leaks: What to Watch For

Whatever the piping material, a gas leak is an emergency. Natural gas and propane are odorized with a sulfur-like smell often compared to rotten eggs. If you smell gas, leave the house, avoid operating switches or anything that could spark and call the gas utility or 911 from outside. Our gas leak smell guide explains what to do step by step.

Signs that a CSST line may have been damaged, beyond odor, include:

• Visible burn marks, melted jacket or small holes on the tubing after a storm.
• Scorch marks on nearby metal ducts, wiring or framing where tubing passes close by.
• A hissing sound near gas piping.
• Appliances that suddenly will not light or stay lit after a lightning event.

After a known nearby strike, especially one that damaged electronics in the house, having a licensed professional check the gas piping is a sensible precaution. A licensed plumber or gas fitter can perform a pressure test to confirm whether the system holds; see our gas line pressure test guide for how that works and when utilities require one.

After a nearby lightning strike

If lightning strikes the house or very close by, a reasonable sequence is:

1. Get everyone out if there is any smell of gas, smoke or visible fire, and call 911 from outside.
2. Once the fire department or utility clears the house, have the gas utility or a licensed plumber check for leaks before relighting appliances.
3. Ask a licensed electrician to look at the panel, grounding and any CSST bonding, especially if electronics, garage door openers or appliance control boards were damaged.
4. Document damage with photos for an insurance claim, and keep invoices for inspections and repairs.

Damage from arcing can be small and hidden inside a wall or floor cavity, so the absence of visible scorch marks does not rule it out.

Physical damage and support

Because the tubing is thin, it can also be damaged by nails, screws or careless remodeling. Codes require protection such as striker plates where concealed CSST passes through framing near surfaces. ASHI notes that inspectors can check support of visible tubing runs, that metal hangers are currently required and that plastic clips have been permitted in the past. CSST should not be used as a hanger for other items, kinked or left lying loose across attic insulation where it can be stepped on.

What Home Inspectors Can and Cannot Determine

The ASHI Standard of Practice requires inspectors to inspect fuel storage and fuel distribution systems and to describe the location of main water and fuel shut-off valves. With CSST, though, much of the piping is hidden in walls, floors and ceilings. ASHI’s guidance states that the inspector’s responsibility has been defined and limited to identifying the CSST installed, and that the inspector is not required to determine whether bonding is required, whether it has been performed or whether it was done correctly or effectively.

In practice, an inspector might:

• Identify CSST at the meter, appliances, manifold or exposed runs and note the jacket type.
• Note whether a bonding clamp and conductor are visible, without certifying them.
• Report missing markings, damaged jackets, inadequate support or unprotected runs.
• Recommend evaluation by a licensed electrician for bonding.

ASHI notes that a few states require inspection reports to include a CSST statement explaining that manufacturers believe the product is safer if properly bonded and grounded, and that proper bonding can only be determined by a licensed electrical contractor. Even where not required, many inspectors include similar language. For more on how inspectors evaluate furnaces, water heaters and fuel-burning appliances, see our heating and cooling inspections hub.

Correction Options and Costs

When an inspector or electrician finds that CSST lacks proper bonding, the fix is usually straightforward. As a rough 2026 guide, not a quote:

• Electrician evaluation of existing bonding: often a service-call charge, sometimes rolled into the repair.
• Installing a bonding clamp and conductor to the grounding system: commonly a few hundred dollars, more if the conductor must travel a long distance or through finished spaces.
• Gas pressure test after suspected damage: often a few hundred dollars, depending on the system and the utility’s requirements.
• Repairing a damaged section of CSST: varies with access; opening finished walls or ceilings adds cost.
• Replacing CSST with black iron pipe or black-jacketed CSST: can range from several hundred dollars for a short run to thousands for a whole-house repipe.

Permit requirements for gas and electrical work vary by Colorado jurisdiction, and many require permits for both. Use licensed, insured professionals and ask them to reference the specific manufacturer’s installation instructions for the tubing in your home.

Gas line additions deserve extra scrutiny

Many CSST runs were added after the original build to serve a new range, an outdoor kitchen, a fire pit, a garage heater or a basement fireplace. Those additions are where bonding, support and protection details are most often missed, and some were installed without permits. Outdoor runs need to be protected from physical damage and sunlight according to the manufacturer’s instructions, and underground runs generally call for materials and methods approved for burial. If a home has gas appliances in locations that look like later additions, ask who installed them and whether the work was permitted and inspected.

Insurance and disclosure

Some homeowners ask whether CSST affects insurance or resale. Practices vary by insurer and state, so the most reliable step is to keep documentation: who installed the system, when bonding was added or verified, and any electrician or plumber invoices. That paperwork answers the questions a buyer, an insurer or a future inspector is likely to raise.

Questions for buyers and sellers

• Does the home have CSST, and what brand and jacket type?
• Is there a visible bonding clamp and conductor, and who installed it?
• Has the home had any lightning strikes, surge damage or gas leaks?
• Were permits pulled for any gas line additions, such as a range, grill or fire pit?

For more on choosing an inspector and what an inspection includes, see our guide to hiring a home inspector.

References

• Inspecting Homes with CSST Gas Piping — American Society of Home Inspectors
• ATF Investigation Report on Lessons Learned from 2 LODD — U.S. Fire Administration
• Corrugated Stainless Steel Tubing and Flexible Appliance Connectors — American Society of Home Inspectors
• ASHI Standard of Practice for Home Inspections — American Society of Home Inspectors

Not sure whether the yellow tubing in a home you are buying is bonded? Talk with us about scheduling a Front Range inspector who identifies gas piping and flags it for the right specialist.