Copper Fuel Gas System FAQs (Frequently Asked Questions)

The Fuel Gas section of this web site contains design guide information for industry professionals interested in using copper tubing for fuel gas systems. Design guides and data sheets are available electronically (and some in print) in our Publications section. If there is anything further we can do, please do not hesitate to email us.

CDA has a sizing calculator (Publication A4030) that simplifies sizing copper tubing for any fuel gas distributions system.

The National Fuel Gas Code (NFPA 54/ANSI Z223.1) and all of the major model building codes have approved copper for the use in fuel gas systems. In fact, in states like Minnesota, Alabama, Georgia, Florida, etc, copper is the dominant, if not the primary choice, for flexible fuel gas piping systems in homes and multi-family units. IAPMO approved copper for use with fuel gas in 1999 - you may want to read the announcement.

The installation of fuel gas systems in Massachusetts is governed by the 248 CMR Massachusetts State Plumbing and Gas Fitting Code in which unlined copper tube is not permitted for natural gas transmission or distribution. Although the code references the allowable use of tin lined copper tube for fuel gas applications. 248CMR also references NFPA 54, which is the National Fuel Gas Code and this code does allow the use of copper tube for fuel gas if the gas supplied contains less than 0.3 grains of hydrogen sulfide per 100 standard cubic feet of gas. Elevated levels of hydrogen sulfide in the gas stream can react with copper tube and can cause flaking of copper oxides on the inside of the tube.

Any fuel gas lines installed using copper tube must be brazed using a filler metal containing less than 0.05% P (phosphorus) and a melting temperature greater than 1000 degrees F. The only filler metal (trade and industry standard) that contains less than the 0.05% P would be an AWS BAg type alloy (according to the American Welding Society's AWS A5.8 specification). In no case should solder or "soft-solder" be used to join copper tube and fittings in fuel gas systems.

See below.

Copper Development Association Inc. is a not-for-profit trade association representing the U.S. copper, brass, and bronze industry, and as such does not sell or distribute product. However, the copper tube that you are looking for can be purchased at any local plumbing, heating or refrigeration supply shop in your area. For contact information of manufacturers of copper tube and fittings, please visit TPF Council page.

The ASTM standards that address the manufacture of the different types of copper tube allowed for fuel gas distribution do not require that the tube carry the ASTM logo or stamp, or standard designation. These standards do outline specific product identification requirements for copper tube made to these standards. This generally includes marking of the tube to include the type of tube (K, L, M, ACR, etc.), name or trademark of the manufacturer, or both, and the country of origin. Depending on the type and temper of the tube, and the standard to which it was made, this marking may be in the form of a permanently incised mark, a painted or inked label, or both. Regardless of the form of the mark, each must include the required information and are repeated throughout the length of tube at regular intervals (no more than every 18 inches for the incised mark or 3 feet for the painted label). The painted/inked marks also give an indication of the tube type by the color of the label: green for Type K, blue for Type L and red for Type M. Also, regardless of the type of copper tube being used, all of the copper tubes manufactured to the standards approved for fuel gas distribution are seamless copper tube.

More information regarding the identification and properties of copper tube for fuel gas applications can be found in Fuel Gas section, in the Fuel Gas Design Guide, and in the Copper Tube Handbook.

There have been some attempts to mandate and standardize specific marking requirements to identify gas lines, even to the extent of requiring specially marked copper tubing. However, for the most part these have been unsuccessful, primarily due to the number of local or regional practices of identifying these lines.

That being said, you should check your local building codes and/or gas utility requirements for the marking and identification of gas lines. In many cases, jurisdictions that allow the use of copper tube in fuel gas distribution systems have specific marking requirements (as they do for all piping materials in this type of system). For an engineered system you should also be sure to check the engineer's specifications for any specific marking requirements.

In most cases the requirements for marking copper tube in fuel gas systems state that the tube shall bear an appropriate label (usually yellow with black writing indicating that the line is a fuel gas line) that is placed in certain intervals along the length of each pipe run (our design guide recommends a maximum interval of every six feet), and within so many feet of either side of a wall, floor or other penetration. We have seen many different ways to accomplish this marking such as contractors who require that the coil of tube be spray painted yellow prior to installation (the installer simply lays the coil of tube on the ground and spray paints one side) and then appropriate labels be placed following installation. Also, to accomplish this identification, tube is also available that has a continuous yellow plastic coating the entire length of the tube.

As far as the nail or screw strike, we also have specific installation requirements in our design guide, and that are also stated in the codes governing these types of installations (NFPA 54/ANSI Z223.1, UPC, UMC, IFGC, etc.), to address this concern and prevent penetration of the tube wall by nails or screws. Unlike rigid piping systems (steel), these requirements are designed to allow the tube to move within the hidden wall space so when it is struck with a nail or screw that they do not penetrate the wall but simply move the tube to the side. Where the tube must be held rigid, such as where it passes through the floor sill or ceiling plate, or where it passes through joists or studs, it is required that the tube be protected with a striker plate. It is also recommended in our design guide that the holes through building members through which the tube must pass be at least 1-1/2 times the outside diameter of the tube, thus allowing some amount of movement to avoid penetration of the tube wall by a nail or screw strike. The curvature of the tube coupled with the freedom of movement that these requirements allow prove very effective in allowing nails and screws that strike the tube to simply deflect to either side of the tube and prevent penetration of the tube wall.

The Fuel Gas Design Guide contains a wealth of information on the proper design, specification, and installation of copper fuel gas distribution systems that exist to make this system as safe or possibly even more safe than rigid piping systems. 

In certain areas of the country it has been against the code to install copper tube for natural gas distribution. This was primarily in areas of the country that utilized the Uniform Plumbing Code, predominately in the West, and most actively in California.

However, at that same time many other areas of the country were successfully installing copper tube in both natural gas and LP gas distribution systems. Many of these areas have been installing copper tube for natural gas distribution for better than 35 - 40 years (Minnesota, St. Louis, Atlanta, Washington D.C. among others) and for most of the country copper tube has been the standard material for LP gas distribution much longer than that.

In the beginning, the reason for this disparity throughout the country in the acceptance of copper tube for this use had to do with the gas being supplied. In the southwest area of the country sour gas (gas containing a significant amount of hydrogen sulfide) was not uncommon, and the use of copper tube in a gas stream containing significant amounts of hydrogen sulfide and moisture lead to the black flakes to which you refer. It should be noted that this was generally encountered in natural gas systems, not LP gas systems (LP being a manufactured gas was more closely controlled with regards to contaminants). However, in the rest of the country the natural gas being supplied did not contain such high concentrations of hydrogen sulfide, allowing for the successful use of copper tube. This was reflected in the codes and standards used throughout the rest of the country allowing copper tube for this use (such as the NFPA 54 National Fuel Gas Code, the BOCA National Mechanical Code and the SBCCI Standard Mechanical Code).

In the last 35 - 40 years, the cleaning and distribution of natural gas throughout the country has improved greatly, especially with the development of regulations strictly limiting the amount of hydrogen sulfide and other contaminants that could be distributed in the gas stream, especially for those gases being supplied over nationwide, inter-linked gas distribution pipelines/systems. These regulations limit the hydrogen sulfide to such a level that it should no longer be available in large enough quantities to promote the black flaking that you had seen in the past.

Recognizing this fact, and the fact that the use of copper tube for the natural gas distribution system allowed gas utilities and building owners to provide natural gas as a cost effective alternate energy source to electric, has led many areas of the country that previously banned the use of copper in this use to reevaluate their position. Most notably, the Pacific northwest (Oregon and Washington especially) have recently begun to aggressively promote and use copper tube for their natural gas distribution systems, regardless of the restriction in the Uniform Plumbing Code.

Following suit, IAPMO, through the use of the consensus process voted to change the Uniform Plumbing Code to lift the restriction on the use of copper tube for fuel gas distribution systems. These changes were published in the 2000 edition of the UPC and UMC.

However, since all natural gas supplies are not necessarily delivered via pipelines regulated by the above regulations, all of the codes allowing for the use of copper in natural gas distribution systems do contain the restriction that bare copper tube not be used if the gas stream contains an average of more than 0.3 grains of hydrogen sulfide per 100 standard cubic feet of gas. Should the gas stream exceed this amount, the codes permit the use of copper tubing if the tube is tin-lined. These requirements are in place to minimize the possibility of flaking inside the copper and to ensure an efficient and successful use of copper tube for this application.

You will find more information on the proper use of copper tube in fuel gas distribution systems in this web site. For more information on the use of copper tube in your particular area, please contact a CDA Project Managers & Piping Applications Specialists.

NFPA 54 does not stipulate whether the fittings have to be forged or machined, only that they be of copper, brass or bronze.

While we cannot size the line for you, we can tell you where you can get the proper sizing information so that you can do so. If you click on the Fuel Gas Design Menu on the right-hand sidebar and click on the link for "System Sizing", it will give you the appropriate information and links to the appropriate capacity tables for copper tube. Besides the information that you listed in your request, you are also going to need to know at what pressure your system is operating (standard or elevated pressure) so that you can use the proper sizing table. You will also need to factor in the type of gas as it indicates (natural or LP) and what the approximate heating value of the gas is (as an example a good rough approximation for natural gas is usually assumed at 1,000 BTU/cu. ft.).

As far as the type of the copper to use, from a pressure standpoint type K or L would be fine, however if you are running this exposed outside you may want to stick with type K to guard from any incidental external damage.

As an example to help you out. Assuming your system uses natural gas with a heating value of 1,000 BTU/cu. ft., and is a standard low pressure gas system (less than 14 inches of water column), your line would need to be sized to deliver 100 CFH (100,000/1,000). From Tables 3 and 4, you can see that for a low pressure system with either 0.5 inch wc or 1 inch wc pressure drop a 1" nominal type L or type K tube (1 1/8 inch OD) tube would be adequate to supply this flow rate for a 60-ft length, and would even be adequate for the entire 100 - 110 foot run from the supply in the house.

Copper tube has been accepted for fuel gas distribution in all of the national model codes in the United States, including the Uniform Plumbing and Mechanical Codes, the National Fuel Gas Code, and the International Fuel Gas Code. However, these codes are simply national models for state, city and local jurisdictions to follow. The model codes referenced are actually standards and do not have the power of a code or law until a jurisdiction adopts them.

You should check with your local Building Department to see if they allow copper tube for natural gas distribution. Unfortunately, even though copper tube has been recognized as an acceptable alternative for natural gas distribution throughout the United States, not all local jurisdictions allow for its use at this time, and it is the local jurisdiction whose codes have the force of law.