Short definition
CSST (corrugated stainless steel tubing) is a thin-walled, flexible gas pipe used in many homes built or remodeled since the 1990s. Most has a yellow plastic jacket; newer “arc-resistant” versions have a black jacket. CSST must be electrically bonded to the home’s grounding system to prevent lightning-induced punctures.
What it is
CSST is a corrugated 304 stainless steel tube, usually 3/8″ to 1″ inside diameter, in a colored polymer jacket. It snakes through wall cavities and joist bays the way Romex wiring does, joining the gas meter to each appliance with brass mechanical fittings listed for that specific brand. Common product lines include Gastite, TracPipe, and Pro-Flex.
The advantage over rigid black iron pipe is speed and flexibility — CSST routes around obstructions in a fraction of the time threaded steel takes to plan, cut, and assemble. Each manufacturer system is listed as a kit under ANSI LC-1 / CSA 6.26, and installers carry a one-time training card from the manufacturer.
The trade-off is electrical sensitivity. The wall is thin, and a nearby lightning strike can induce voltage on metal in the home. If CSST isn’t electrically bonded to the grounding system, that voltage can arc through the jacket and burn a pinhole in the tubing — and ignite escaping gas.
Why it matters to a homeowner
If your home has yellow flexible gas lines and no visible bonding wire connecting them to the electrical service ground, your home is missing a code-required safety feature that became mandatory after a series of lightning-induced fires were investigated nationally. Adding the bond is a one-time, inexpensive fix; ignoring it leaves a known gap.
When a home inspector writes “yellow flexible gas line, no bonding visible” on a report, this is what they mean. Adding a #6 AWG copper bonding clamp from the CSST manifold to the service ground typically runs $150–$300 with an electrician — small money relative to the lightning risk in a house that already has the system installed.
When you’ll encounter this term
- A home inspection on a 1995–2010 home flags a missing CSST bond
- A new gas appliance install with the contractor running CSST through walls
- A lightning strike or near-miss in the neighborhood prompts a re-check
- Selling a home: inspectors increasingly check for the bonding wire
- A remodel involves cutting into existing gas runs and the contractor mentions the brand-specific fittings
Common variants and disambiguation
- Yellow-jacket CSST (traditional): requires a direct, dedicated bonding conductor — typically #6 AWG copper — clamped to the manifold and run to the service ground per IRC/IFGC since 2009.
- Black-jacket CSST (arc-resistant, e.g. FlashShield, CounterStrike): newer products recognized by 2018+ code as not requiring the additional direct bond beyond the standard NEC 250.104(B) gas-piping bond, if installed strictly to the manufacturer’s listing.
- CSST vs. black iron pipe. Black iron is rigid threaded steel; the legacy gas-piping standard. Slower to install but electrically robust.
- CSST vs. flexible appliance connector. A flexible appliance connector is the short coated stainless line (12–60″) at the back of a range or water heater. CSST is the in-wall distribution system. Different products, different rules.
Common failure modes
- Missing or improper bond. A 2008-era yellow CSST install with no bonding clamp is the classic finding. Lightning on a nearby tree can pinhole-burn the tubing; gas leak; fire.
- Jacket nicked during framing. Non-arc-resistant CSST relies on jacket integrity for arc resistance.
- Improper bend or kink. Tubing crushed at a fitting; flow restricted; corrugation root can crack.
- Wrong fitting paired with wrong brand. Each manufacturer’s fittings are listed only with their tubing — not interchangeable.
- No grommet through stud or plate. Tubing abrades on metal edges over years.
Washington note
Washington adopts the IFGC and IRC by reference through the State Building Code Council (chapter 51-52 / 51-51 WAC), so the CSST bonding rule applies statewide. NEC 250.104(B) requires gas piping including CSST to be bonded to the electrical service grounding system; manufacturer instructions plus 2009+ IRC/IFGC require the dedicated bonding conductor on yellow CSST.
For paid CSST work: inside Seattle city limits, a Seattle Gas Piping Mechanic license is required. Statewide, paid gas-pipe installation requires a registered contractor under chapter 18.27 RCW. King County publishes a homeowner-facing reminder to hire a registered contractor for gas-piping work. CSST is not a DIY installation in WA — manufacturer training and a permit/pressure-test are part of every legitimate job.
If your home has CSST and you’re not sure whether it’s bonded, a licensed electrician or gas-piping contractor can confirm during a routine visit. If it isn’t, add the bond. This is the simplest, cheapest CSST safety upgrade.