Q&A / 

Flexible Gas Lines- Are You Serious?

! ! ! See Author's Notes at Bottom of the Column ! ! !

DEAR TIM: The natural gas lines that are being installed in our new home are not the heavy black iron pipe. They are a new flexible stainless steel piping system that is installed like electrical wire. What is this material? Is it safe to use? Are there advantages to using this pipe? Can you cut into the pipe at a future date to install an added gas appliance? Is there another alternative gas piping material? Betsy F., Augusta, GA

DEAR BETSY: Congratulations! You are now the proud owner of some wonderful corrugated stainless steel tubing (CSST). This material was approved for residential use in 1988 by the National Fuel Gas Code. It is an ingenious method of supplying natural gas to fireplaces, furnaces, cooktops, clothes dryers and any other gas appliance. Virtually all state and local code authorities permit its use and many contractors are finally embracing it.

Here are two short pieces of the flexible stainless-steel gas lines. You can practically tie it in a knot it is so flexible. If you have lots of pipe to run, this may be the way to go.

Here are two short pieces of the flexible stainless-steel gas lines. You can practically tie it in a knot it is so flexible. If you have lots of pipe to run, this may be the way to go.

I remember when the material was first introduced. Many of my fellow contractors who install gas lines thought it was unsafe. Their arguments never made sense to me. For as long as I have been in the home building business, we always used similar brass appliance connector tubing when gas was supplied to a clothes dryer, a cooktop, or a gas range. Hundreds of thousands of houses have these corrugated appliance connectors in service right now. They have worked swell for many years.

The CSST has many advantages. Perhaps the biggest one is labor savings. Traditional black iron pipe takes a lot of time to cut and thread. I know as I have installed thousands of linear feet of the heavy material. As you said, the new CSST is installed like electrical wire. You simply pull the material between two points and cut it to length with simple tubing cutters. Black iron pipe is the exact opposite. A typical black iron pipe installation requires a professional to precisely measure, cut, and thread the individual pieces of pipe. All of these steps are very time consuming.

When you use CSST, you can minimize potential gas leaks. A typical black iron pipe installation has many 90 degree, tee and coupling fittings. These fittings are used each time you change directions or join two pieces of straight pipe together. Each of the cast fittings can be the source of a leak. What's more, the threaded joints on both sides of the fitting can also be potential leak points. Because the CSST snakes its way around bends and obstructions as one solid piece of tubing, you only have a fitting at each end of the line. If you do have a leak, these fittings are almost always readily accessible for adjustment.

Working with CSST is not really a do-it-yourself proposition. Many of the manufacturers of this material require professional installers to take a short training course that familiarizes them with the small nuances of this unique gas piping system.

This is traditional black iron pipe. Each end of a piece of pipe must be threaded. It is messy and hard work, but I must admit I sort of enjoy it.

This is traditional black iron pipe. Each end of a piece of pipe must be threaded. It is messy and hard work, but I must admit I sort of enjoy it.

Adding additional gas lines at a future date is not a problem if you plan for the possibility during the original installation. The CSST systems can be installed one of two ways: a series or parallel installation. The series installation resembles traditional black iron piping. A larger diameter main line CSST pipe supplies gas to smaller branch tubes that feed each appliance. This is often the easiest system to adapt at a future date. A parallel CSST system mimics an electric panel. All of the gas lines that feed each appliance start at a central distribution point. To add a line in the future you need to have an extra gas port on the manifold within the panel.

If you are not able to get CSST tubing and can't handle working with black iron pipe, consider using soft copper. It offers all of the same advantages of the CSST systems. Soft copper is approved for interior residential gas piping in many cities and towns. You don't solder it like water lines. Connections are made with common flare fittings that tighten with standard wrenches. The only specialized tool you need is a flaring tool made to fit the pipe size you are working with. If you use copper for gas lines in your home, be sure to label them so a future weekend warrior doesn't mistake them for a water line!

Author's Notes:

On November 8, 2005, I received the following email.

In regard  to your article on the CSST systems being installed in new homes. If you care to, read an article that was published in April of 2003 in the Dallas News regarding banning this installation in the city of Frisco, Collin County, Texas. Lightning strikes have caused numerous fires in residential homes as a result of  CSST failing. Although the manufacturer states that it is completely safe, in fact safer than ridged black pipe, it has some serious issues. I have seen three fires in our own community as a result of CSST failure. The manufacturer accepts no responsibility for improper installation, and does not provide in any great detail, of detrimental or catastrophic failure if done so. I just saw your article and thought I would provide feedback. If you have questions on the article I mentioned, you may contact the Dallas News. Thank you for your time.

Maxwell J. Brunner
Menomonee Falls Fire Department
Email- maxbrunner@menomonee-falls.org


I responded to this very interesting email with a few thoughts of my own. My first suspicion would be that the tubing acts like a lightning rod of sorts. The thin walls of CSST might not seem to handle as much of a strike as black iron. Black iron is so much thicker that it may actually take a lightning strike better.

I suggest you look up the article in the Dallas News if you want more details.

Column 296


31 Responses to Flexible Gas Lines- Are You Serious?

  1. Lightning strikes have caused some revisions to be made to the installation instructions for CSST. Arcing between the CSST and electrical lines was found to be the cause of these fires.

    The gas line is now required to be grounded and BONDED to the electrical system. This is usually accomplished by connecting the CSST gas line to the main ground rod with ground clamps and #6 solid copper wire.

    The 2009 editions of the International Fuel Gas Code and the Uniform Plumbing Code state in Section 7.13.2: "CSST gas piping systems shall be bonded to the electrical service grounding electrode system at the point where the gas service enters the building. The bonding jumper shall not be smaller than 6 AWG copper wire or equivalent."

    When the CSST piping is installed properly there is no more danger from lightning strikes that with any other gas system. Most manufacturers supply instructions on how to properly install ground clamps.

    I just installed a furnace in my attic with CSST piping. It was a little more expensive materials wise but saved me a lot of headaches with the complex bends and turns that were required to connect the gas line. It took me approximately 2 hours to run a CSST gas line that would have probably taken a full day of cutting and threading cast iron pipe.

  2. If there is a problem with lightening strikes why don't they put a insulating type pipe at certain points to prevent the csst from being grounded making it safe from strikes. Or use pure plastic lines that are tough enough for the job. I can't believe in this modern time we only have three choices for gas lines.

  3. Tim,

    I read your article and agree. I also read the email from the fireman. Rest assured, as an electrician we are already being told of the situation and in New York State, we are now required to bond the gas lines to the main electrical grounding electrode, in order to make sure such problems don't happen or are extensively minimized.

  4. What is meant by "bonded gas line"?
    We hired a contractor to convert an attic mounted heat pump to gas. They ran CSST from the basement to the attic alongside the refrigerant lines. Very neat install. They did attach a solid copper ground wire between the gas meter and main electrical ground using wire clamps, but how can I tell if it is "bonded"?

    • Garry,
      "Bonded" simply means that there is a physical wire/electical coupling between the conductive materials (Only the grounded materials of course). The goal here is that the CSST and the elecrical circuit share the same path/circuit to potential earth, or ground. A meter or a visual check gould help you, but remember, residential 120V is the most deadly. If you don't know electrical, do what Tim says and call a pro.

  5. Is there a metal gasket inside the end of the flexible pipe to keep the pipe from twisting? I unscrewed the pipe and it looks like half of one fell out. Can I just replace the end with another end piece with the gasket in it?

  6. I've heard of the lightning issue and assumed there was a way to protect against it. It sounds as if that assumption was right; knock on wood. But my objection to any flexible gas lines in the walls of a house concerns what happens when someone tries to put up a big picture, shelving, framing for new partition, just about anything that would require screws or nails into the wall. Most people do this without a thought of hitting anything sensitive, and I'm aware that they hit water pipes and even cables from time to time, but the risk from hitting a gas line seems much higher. Are there any places where such lines require steel conduits when run in closed up dead space? Seems like a small price to pay for peace of mind.

    PS: Robert M. has an interesting point. I know plastic tubing (HDPE, PEX-AL-PEX, etc.) has been used underground for years. But I wonder if pure plastic would eliminate the risk for lightening strikes; there is, I believe, some water accumulation in these systems, and a resistive path could be even more dangerous than a direct short. I can imagine a pipe heating up and bursting if the right current makes its way through the moisture, thought I can't say for sure how plausible that would be. Similar questions must come up when water lines that had been used for grounding are spliced with plastic.

  7. Isn't all natural gas line buried and most come out of the ground in
    the black pipe, question is do I still to ground the flexible line?

    • Yes, most natural gas lines are buried. You need to install the pipe according to all LOCAL regulations. Contact your gas supplier for instructions. DON'T GUESS or LISTEN to advice from others online. Don't HOPE you're doing it right. Contact the gas supplier.

      • Underground metal pipe as installed by the gas company is coated and cathodically protected (CP), meaning that a negative voltage is imposed on the material to prevent corrosion using anodes or rectifiers. As long as the pipe is more negative than the surrounding soil, the metal will not rust. In order to maintain this negative potential, the pipe is coated (as best as possible) to isolate it from the soil and has an insulator installed at the meter to prevent a home's AC grounding electrode system from bleeding the CP voltage off. LDCs (local gas distribution companies) frown on the practice of grounding their CP protected pipe.

  8. Could you use a grounding rod near the entrance of the gas pipes into the house instead of running a wire all the way back to an electrical panel that is in the opposite end of the house. It would be grounded by ground rod correct?

  9. You must run the ground wire back to the panel. If you drive another ground rod there will be a difference in potential. The bond must go back to the GES grounding electrode system.

  10. When I attach my #6 ground wire to my flex gas line fitting, can I just attach the running length of the ground wire to the side of my brick on the house as it makes its way to the panel box on the inside of my home. Thanks

  11. I am considering using the yellow flex line to run from the basement up through the old fireplace ash shute to connect to a set of vent free fireplace logs in an existing fireplace. Is this something that would be safe?

    I am also looking for step by step instructions from someone who may have done this type of install before.

  12. I am in the process of changing out my CSST. First of all after it was installed everyone in the house would hear a high pitched ring when the furnace and stove ran at the same time. If you have high pressure gas ringing through the lines at too quick of a rate the lines can hum or ring. In our case we had xcel come out and they said they see it all of the time. Manufactuer acknologed this issue. As far as the safety issues they are very real even if you bond it correctly the issue is really the thickness or in its case thinness of its walls. Soft copper has none of these issues and is fairly easy to work with. I would stay away if you can.

  13. I install gas lines for a living. I am also a firefighter. This gas line, the yellow stuff is great if properly installed. There is a new type hitting the market. It's coated with rubber to resist lighting issues. You can cut down on the whistling noise simply by going to the shut off up stream and turning it down till the noise stops. Your slowing the speed of the gas going thru the pipe. That's the issue. It cannot be installed in fireplaces.

  14. This article and it's associated comments were fantastic, helpful and informative for a new homeowner like me.

    I'm having my 26 year old Trianco Heatmaker boiler replaced soon with a Bosch Greensaver 100 Combi propane boiler in my basement. The install will be done by a large, local energy company here in Maine.

    When the energy company representative came over he measured out rooms, checked our forced hot water baseboard in each room, checked our boiler and took pictures of it. During this process, he mentioned that our CSST line needed to be grounded, and that getting my own electrician would be cheaper than what his would charge.

    I'm wondering what this work would typically cost. My CSST line runs through the basement ceiling near the circuit breaker, and my rudimentary understanding is that it would require a clamp and copper wire to the main ground.

    I'm wondering what the typical local electrician might charge for this, as the energy company representative seemed to imply that it's expensive.

    Thanks in advance for any possible help.

    • Just a quick update. I'm told that I need to have #6 copper wire run from the grounding bar at the main circuit to the pipe where the gas first comes in outside, secured with a clamp and some scrubbed section of pipe.

      I'm told the wire can be stapled to joists along the basement ceiling to the circuit breaker box.

      My question was whether this would be a huge expenditure or not, and I'm now being told by the energy rep that it won't be a massive expenditure.


  15. I have been reading all the informative emails from other professional gas line installers and fireman and trying to understand the grounding/bonded issue for using CSST....My question deals in that I already have the black iron pipe 3/4" thick for my gas line coming into my house which has been installed throughout my house which was built in 1987 and I wanted to reroute the existing gas line from it's current location in one wall on the main level (flipping my kitchen into my dining room) and it would be better suited to reroute the gas line using the flexible CSST to snake around already installed vents and air ducts running into my basement and instead of using the more rigid black pipe which might be hard to install around those confined spaces.
    So my question is would I still need to ground/bond the flexible CSST if I am hooking it up to the existing Black Gas line in my home?

    • Bruce,
      Yes as far as I know you would need to ground/bond any CSST in your home. The black iron does not insulate CSST that may be connected to it

  16. I have read all of the emails and questions concerning CSST and it's use. I like the response of "What does your local Electrical Inspector say?" & "What does your local Building Inspector say?" I have been working with these "Inspectors" for years ands can tell you that they can read the code book but interpreting it and putting the code to practical use in the field are two totally separate things altogether. First, yes the installation of CSST takes less labor time. That is where the advantages end for me and for anyone with some knowledge about building practices and common sense. The Black Iron pipe is "sized" for the amount of gas appliances intended to be installed and used in the home. This MUST be done by a professional that knows how to use the gas sizing charts in the code book. The same is required to be done for the use of CSST. This practice is commonly overlooked and also many times undersized gas piping is not caught by "inspectors". Black Iron Pipe is cut and threaded and does take a lot of time, knowledge and expertise to install correctly, (it is Gas, how do you want it contained in your home?) the system is then pressure-tested with air at pressures above what it will endure when the gas is finally introduced. If there are any leaks in the system, they must be corrected at that time. Same as CSST. Tim's statements make it seem as though leaks occur from time to time and it is easier to fix them and the potential is greater when using Black Iron Pipe, nothing could be further from the truth.


    Please go back and re-read what I said. My comparison is that with CSST you only have a leak potential at each end of the run where you have a fitting. With black iron - and I've installed THOUSANDS of feet of it - you have a leak potential at each side of each fitting as you install the pipe throughout a house. In one run, you may have ten or more 90's, couplings, tees, etc.!


    There is always a potential for a leak in ANY system utilized. When installed by a Licensed and Insured Professional Plumber the chances are minimized and then eliminated when a proper inspection/pressure test is done. If one adds up the amount of hours spent worrying and contemplating the grounding and bonding issues associated with the use and installation of CSST, how much labor did you really save? This CSST and other like materials to save on labor was embraced by builders who wanted to save money on labor. One question, did the price of the house go down? Answer: NO
    The labor savings went into the builders pocket. Like many of the other products introduced into the marketplace as being "just as good" or "think of the money saved on labor" Why do we want to eliminate the professionals from the marketplace? When there is a problem the builder or consumer can't solve, they call a professional to solve it and usually complain about the price, why? They saved all this money on putting in cheaper, less labor-intensive materials and now want to scream when it ends up costing them the same and they don't have near the quality of product in the end.The attitude of "It's somebody else's problem when I sell the house" is ludicrous. If everybody has that outlook/attitude, who are you buying your next house from and what attitude do they have?! Soft copper simply should not be used on Natural Gas, the odorant that they put in the gas has been shown to "eat away" at the copper over time, you don't see this because the gas is on the inside of the pipe doing the damage. A professional sees this when they take apart the pipe or are working on gas appliances a few years labor and notice all of the black flakes in the gas system. Do your research, better yet, hire a licensed professional. Stop trying to "save a Buck" on something that could kill you in the end.

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