Want to learn all about flex line gas code and proper installation? You are in the right spot!
In this guide, you'll learn:
- The 4 most common code requirements for flexible gas lines or CSST
- 4 typical manufacturer instructions for proper installation of flex gas lines
- And some frequently asked questions on flexible gas lines
Over the years I have inspected so many homes with flexible gas lines, also known as CSST.
This flexible gas piping has a very thin metal wall, only about 0.3-mm thick, and it can become a fire hazard if improperly installed. And that's why I wanted to create this guide, to educate homeowners on the potential hazards of flexible gas lines and to bring them up on current code.
Keep reading to learn some of the most important code requirements for flex gas lines and to see the common manufacturer instructions for CSST installations. Let's get to it!
What Is Flexible Gas Line Code?
Flexible gas line code is a set of government regulations that controls flex gas line installations.
Flexible gas lines (also known as corrugated stainless steel tubing - CSST) have been installed in millions of homes in the U.S. and around the world.
International Residential Code
The most common source of building code is the International Residential Code or the IRC. This code is updated every 3 years and it is known as a model code.
Many U.S. states and foreign countries use the IRC for their building code, sometimes with matching language.
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Verify Your Local Code (And Manufacturer Instructions)
This guide isn't meant to detail every code, and I have summarized a few of the most important codes for flex gas lines from the IRC Chapter 24 Fuel Gas.
Always verify the flexible gas line code with your local state or city and with the manufacturer. It is also important to note that the IRC leaves out a lot of installation details for CSST and says to follow manufacturer instructions.
Top 4 Flex Gas Line Codes (2022 Requirements)
- Flex Gas Lines Need To Be Installed With Supports
- Flex Gas Lines Should Be Electrically Bonded And Grounded For Safety
- Flex Gas Line Pipe Size Is Based On A Few Factors
- Protective Covering Is Required Outdoors
Code 1- Flex Gas Lines Need To Be Installed With Supports
CSST needs to be supported at certain intervals with clips or straps.
These supports basically hold the flex gas line in place and help prevent unwanted movement of the gas line. The flexible gas line code in the IRC doesn't explicitly state how often it needs to be supported, but it says you must follow manufacturer instructions on spacing.
Some CSST manufacturers will require a minimum of flex line support every 4-feet, but other companies may only need support every 8-9 feet.
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Code 2 - Flex Gas Lines Should Be Electrically Bonded And Grounded For Safety
CSST needs to be electrically bonded and grounded to prevent damage to the line.
Many U.S. states around 2006 enacted a CSST gas line code that requires electrical bonding of CSST such as this example in Virginia. Studies have confirmed that a lighting strike near a home can puncture the membrane of CSST as result of the power surge.
The International Residential Code doesn't specify the wire to be used for bonding, but it is most commonly a #6 AWG copper conductor and installed where the solid gas pipe gas line first comes into the home.
Flex corrugated gas lines have been involved in a number of lawsuits over the years. Since CSST is a very thin metal at around 0.3-mm thick, it is more vulnerable to lightning strikes. Electrically bonding the CSST will ground the gas line and help prevent damage and subsequent fire risk.
Arc-Resistant Jackets On Newer CSST
However, newer CSST (usually black jacketed, not yellow) has an arc-resistant jacket that is already considered bonded when installed to a grounded appliance such as a furnace.
Homeowners should check with the manufacturer to see if their CSST has an arc-resistant protective jacket. And even if the CSST is made with an arc-resistant jacket, your local city or state may still require bonding.
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Code 3 - Flex Gas Line Pipe Size Is Based On A Few Factors
The pipe size or diameter of CSST will be determined by...
- whether using natural gas or propane
- gas inlet pressure
- pressure drop in the line
- and the length of the pipe
The IRC has two tables to determine pipe size in Chapter 24 for flexible gas lines. You can also see the pipe sizing chart for the manufacturer Gastite here.
One of two tables in the International Residential Code that governs pipe size for CSST
Code 4 - Protective Covering Is Required Outdoors
In some U.S. states such as in Massachusetts, CSST is required to have a metal cover to protect it from lighting and the elements when outside.
Since CSST has a much thinner wall than traditional black iron gas pipe, it should be protected from damage when outside and above ground.
Top 5 Flexible Gas Line Manufacturer Requirements
- Flex Gas Line Should Not Be Connected To Movable Appliances
- Protective Plating Should Be Installed When CSST May Be Punctured
- The Maximum Allowable Bending Radius of Flex Gas Lines
- Sediment Trap Will Likely Need To Be Installed
- Shutoff Valves Will Need To Be Installed
Flex Gas Line Should Not Be Connected To Movable Appliances
CSST should never be directly connected to movable appliances like dryers, washers, and ovens.
A flexible appliance connector should be used instead to connect from the CSST to these appliances. Flexible appliance connectors also have a corrugated pipe except that the corrugation is visible and there is no plastic sheathing.
These short appliance connectors are usually only 12-72 inches long.
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Protective Plating Should Be Installed When CSST May Be Punctured
Protective plates need to be installed to protect flex gas lines from punctures.
Since the CSST gas line has such a thin metal wall (0.3 mm thick) it is important to protect the gas line from nail punctures. If CSST is installed along drywall or in some area where nails may be used, it needs to be protected with metal plating.
The Maximum Allowable Bending Radius of Flex Gas Lines
The maximum allowed bending radius is usually 3-inches for 3/4" CSST and up to 5-inches for 1" or larger CSST.
Plumbers and homeowners will need to follow the manufacturer's requirements and they should not bend the CSST too far.
Sediment Trap Will Likely Need To Be Installed
Sediment traps are short pieces of pipe that capture 'sediment' and other particles that are in gas.
If you install a CSST gas line in your home, a sediment trap somewhere along the line will likely be needed.
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Shutoff Valves Will Need To Be Installed
The manufacturer will specify where and when shutoff valves will need to be required.
But typically, at least one shutoff valve will need to be installed where the flex gas line connects to the 'black iron' or hard gas pipe.
Frequently Asked Questions
How Do I Know If I Have CSST?
The gas line will have a flexible yellow or black jacket. It is important to distinguish CSST from the regular flexible appliance connectors which are NOT CSST. You can also look up the brand or other markings on the gas line.
How Safe Is It?
Flexible gas lines (known as CSST) are safe to use if properly installed in a home. All flex gas lines installed in new homes are required to be electrically bonded and grounded to prevent fire damage from lightning strikes.
If you have an older home with CSST, it is important to verify that the electrical bonding and grounding exists and is working properly. In addition, manufacturers require protective plating to prevent nails from damaging the flexible gas lines.
A qualified electrician or plumber should verify proper installation of the flexible gas line.
What Is The Lifespan?
Flex gas lines or CSST typically have a lifespan of around 30-years. For comparison, 'black iron' gas pipe will usually last around 50-100 years.
Is My Old Flex Gas Line Meeting Current Code?
Old homes with flexible gas lines were up to code when the home was built.
However, new homes with CSST require electrical bonding or grounding to protect against lightning strikes. An older home is likely exempted (grandfathered-in) from current CSST gas line code, but homeowners that have flexible gas lines should have it evaluated by a qualified plumber or electrician.
Just because a home is exempted from current code requirements doesn't mean that the existing flexible gas line installation is safe.
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31 thoughts on “Flexible Gas Line Code (2025 CSST Requirements)”
why cant I bury csst in sand without conduit.
It’s just not designed to handle direct ground exposure, the jacket/sleeve will eventually corrode. Since it is just buried in sand, it can also easily get punctured.
Can you add on to a CSST line if a portion of it may have been damaged in a fire?
I don’t think there is a way to do it unless you replace the entire line back to a manifold. There may be unseen damage or pipe weakness in other sections that aren’t visible. I would have the entire CSST system inspected by a plumber, TBH.
Can CSST be left exposed in a (mostly) finished basement? The builder ran the propane lines across the basement along the bottom of the overhead joists. I’m finishing the basement but do not want to do any ceiling. This will leave the CSST exposed but not at risk of being punctured by a nail.
IRC 2018 G2415.7.2 is worded quite confusingly.
Hey Steve… I think it’s fine since it’s not in the way of traffic or potential puncturing. The entire IRC is confusing, lol.
I seem to recall hearing flexible gas lines like CSST should not be used outside of walls below a certain height inside residential occupancy. As best I recall steel gas pipe should be used below whatever the height was because it is less susceptible to damage. Am I dreaming this or is there a requirement. Thanks for the informative info.
As far as I am aware, there aren’t any specific codes in the IRC or IFGC regarding height restrictions. There are regulations on protecting CSST in conduit or sleeves if it is vulnerable to impact or damage such as in garages but I guess low areas in a utility room or basement could be interpreted as a possible impact area. It’s definitely something to be cognizant of though — that it is much more susceptible to damage than black iron pipe.
Hi, what do you recommend using as an 8 foot long nail plate or protective conduit, to protect flex / csst from punctures? (Floors / walls)
Thank you.
I’d probably just use a standard metal nail plate and use multiple ones together.
ARIE:
I WAS TOLD BY A LOCAL HVAC CONTRACTOR THAT MY GAS LINE WAS RUNNING THROGH MY FURNACE AND THAT WAS ILLEGAL AND NEEDED TO BE “PIPED OUT” I LIVE IN LA, IS THAT CORRECT?
Hey Dan… I am unsure about LA but it is a pretty common local building code, especially in areas of earthquakes such as in LA. Your home may be grandfathered in however to past building code, so I can’t say for sure.
I’ve had my installation in place for about 14 tears. I have rum CCST from my house to a copper manifold. From that manifold, I have 2 extensions, with cut off valves, that go to 2 separate tanks. From the cut off valve, to the regulator on each tank, I have CCST flexible piping (less than 3′) to complete the connection. I was told by a new delivery guy that this is not allowed. As I said earlier, this has been this way for 14 years and I’ve never had this problem with any of the other delivery drivers, all from the same company.
I mean, yes, it isn’t allowed in modern code since it is vulnerable to damage, but your home (depending on age) is almost certainly grandfathered in to new building code. You may just need to hire a different company.