Flexible Gas Line Code (2024 CSST Requirements)

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
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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.

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Top 4 Flex Gas Line Codes (2022 Requirements)

  1. Flex Gas Lines Need To Be Installed With Supports
  2. Flex Gas Lines Should Be Electrically Bonded And Grounded For Safety
  3. Flex Gas Line Pipe Size Is Based On A Few Factors
  4. 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.

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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.

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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

  1. Flex Gas Line Should Not Be Connected To Movable Appliances
  2. Protective Plating Should Be Installed When CSST May Be Punctured
  3. The Maximum Allowable Bending Radius of Flex Gas Lines
  4. Sediment Trap Will Likely Need To Be Installed
  5. 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.

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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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13 thoughts on “Flexible Gas Line Code (2024 CSST Requirements)”

  1. 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.

    Reply
  2. I have a question regarding a metallic flexible pipe connected to the shut off key valve behind the wall. Is this acceptable? I was told that this tubing might become corrosive and will be prone to gas leak. In addition, since the flexible tubing is behing the wall and it is not easily accessible for repair. It would mean that the wall would need to be torn down to access the untwisting of the tubing from the wall key connector. I live in California. Also, it had multiple connectors as it is connected to the shut off valve for the fireplace. I have a photo that would describe it better, if you wish to see it. I would like to know the code related to having a flexible tubing behind the wall. Thank you.

    Reply
  3. What is the requirement for a gas line supply into a furnace ? I am specifically interested in where the black iron pipe enters the furnace as the supply. Is there a code requirement for flexible gas lines ?

    Reply
    • Hey Todd,

      The IRC says you can directly connect to a furnace if you follow manufacturer instructions. However, I think most CSST manufacturers clearly state to avoid penetrating the furnace cabinet such as in this GasTite install manual, “Additionally, Gastite/FlashShield+ shall not penetrate
      metallic cabinet of appliance” on page 60.

      The best practice is to have rigid metal piping come out of the furnace cabinet and then connect the CSST. Most local building code requires a sediment trap or drip leg at the furnace as well.

      Arie

      Reply
    • Hey Johnny,

      I don’t see anything directly in the IRC but other states have explicit codes that it can’t be supported or attached to water piping since it may mess up the bonding. If it runs parallel and doesn’t touch any water piping, I don’t see an issue, but please verify with a plumber or manufacturer. Below is the code language of NY state but I have seen it elsewhere in manufacturer install manuals.

      “[NY] G2411.2.3 (310.2.3) Prohibited Uses
      CSST shall not be supported on or by other electrically conductive systems including copper water pipe, electric power cables, air-conditioning and heating ducts, communication cables and structural steel beams. Electrical wiring, including the bonding conductor, shall be supported and secured independently of the CSST so that it does not come in contact with the CSST.”

      Cheers,
      Arie

      Reply
    • Hey Jeff,

      If you are referring to CSST, it will depend on the manufacturer, so please verify with them. There is no maximum length prohibition in the IRC from my reading of it. However, if you are talking about a standard appliance connector, then the maximum length according to the IRC is 6-feet… “Flexible connectors must bear the label of an approved agency and are limited to a maximum of 6 feet (914 mm) in length”.

      Cheers,
      Arie

      Reply
    • Hi Dave,

      If you are referring to CSST…not just standard appliance connectors…it will really depend on the manufacturer, so please verify with them as there isn’t a prohibition in the IRC as far as I can see.

      Most CSST systems are designed to have the flex pipe as branch lines connecting to the main trunk (rigid pipe) with a T fitting. Connecting two CSST’s together may create a pressure drop and other problems.

      For standard appliance connectors (not CSST), building code prohibits connecting two or more appliance connectors together. This is the IRC language, “Only one connector shall be used for each appliance,” you can see the IRC code here.

      Cheers,
      Arie

      Reply

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