24 CFR § 3280.705 - Gas piping systems.

§ 3280.705 Gas piping systems.

(a) General. The requirements of this section shall govern the installation of all fuel gas piping attached to any manufactured home. The gas piping supply system shall be designed for a pressure not exceeding 14 inch water column ( 1/2 psi) and not less than 7 inch water column ( 1/4 psi). The manufacturer shall indicate in his written installation instructions the design pressure limitations for safe and effective operation of the gas piping system. None of the requirements listed in this section shall apply to the piping supplied as a part of an appliance. All exterior openings around piping, ducts, plenums or vents shall be sealed to resist the entrance of rodents.

(b) Materials. All materials used for the installation, extension, alteration, or repair of any gas piping system shall be new and free from defects or internal obstructions. It shall not be permissible to repair defects in gas piping or fittings. Inferior or defective materials shall be removed and replaced with acceptable material. The system shall be made of materials having a melting point of not less than 1,450 F, except as provided in § 3280.705(e). They shall consist of one or more of the materials described in § 3280.705(b) (1) through (4).

(1) Steel or wrought-iron pipe shall comply with ANSI Standard B36.10-1979, Welded and Seamless Wrought Steel Pipe. Threaded brass pipe in iron pipe sizes may be used. Threaded brass pipe shall comply with ASTM B43-91, Standard Specification for Seamless Red Brass Pipe, Standard Sizes.

(2) Fittings for gas piping shall be wrought iron, malleable iron, steel, or brass (containing not more than 75 percent copper).

(3) Copper tubing must be annealed type, Grade K or L, conforming to the Standard Specification for Seamless Copper Water Tube, ASTM B88-93, or must comply with the Standard Specification for Seamless Copper Tube for Air Conditioning and Refrigeration Service, ASTM B280-1995. Copper tubing must be internally tinned.

(4) Steel tubing must have a minimum wall thickness of 0.032 inch for tubing of 1/2 inch diameter and smaller and 0.049 inch for diameters 1/2 inch and larger. Steel tubing must be in accordance with ASTM Standard Specification for Electric-Resistance-Welded Coiled Steel Tubing for Gas and Fuel Oil Lines, ASTM A539-1999, and must be externally corrosion protected.

(5) Corrugated stainless steel tubing (CSST) systems must be listed and installed in accordance with ANSI/IAS LC-1-1997, Fuel Gas Piping Systems Using Corrugated Stainless Steel Tubing (CSST) (incorporated by reference, see § 3280.4), and the requirements of this section.

(c) Piping design. Each manufactured home requiring fuel gas for any purpose shall be equipped with a natural gas piping system acceptable for LP-gas. Where fuel gas piping is to be installed in more than one section of an expandable or multiple unit home, the design and construction of the crossover(s) shall be as follows:

(1) All points of crossover beneath the transportable sections must be readily accessible from the exterior of the home. In multi-story manufactured homes, the interconnections between stories must be accessible through a panel on the exterior or interior of the manufactured home.

(2) The connection(s) between units must be made with a connector(s) listed for exterior use or direct plumbing sized in accordance with § 3280.705(d). A shutoff valve of the non-displaceable rotor type conforming to ANSI Z21.15-1997, Manually Operated Gas Valves for Appliances, Appliances Connector Valves, and Hose End Valves, suitable for outdoor use must be installed at each crossover point upstream of the connection.

(3) The connection(s) may be made by a listed quick disconnect device which shall be designed to provide a positive seal of the supply side of the gas system when such device is separated.

(4) The flexible connector, direct plumbing pipe, or “quick disconnect” device shall be provided with protection from mechanical and impact damage and located to minimize the possibility of tampering.

(5) For gas line cross over connections made with either hard pipe or flexible connectors, the crossover point(s) shall be capped on the supply side to provide a positive seal and covered on the other side with a suitable protective covering.

(6) Suitable protective coverings for the connection device(s) when separated, shall be permanently attached to the device or flexible connector.

(7) When a quick disconnect device is installed, a 3 inch by 1 3/4 inch minimum size tag made of etched, metal-stamped or embossed brass, stainless steel, anodized or alcalde aluminum not less than 0.020 inch thick or other approved material (e.g., 0.005 inch plastic laminates) shall be permanently attached on the exterior wall adjacent to the access to the “quick disconnect” device. Each tag shall be legibly inscribed with the following information using letters no smaller than 1/4 inch high:

Do Not Use Tools To Separate the “Quick-Disconnect” Device

(d) Gas pipe sizing. Gas piping systems shall be sized so that the pressure drop to any appliance inlet connection from any gas supply connection, when all appliances are in operation at maximum capacity, is not more than 0.5 inch water column as determined on the basis of test, or in accordance with table 3280.705(d). When determining gas pipe sizing in the table, gas shall be assumed to have a specific gravity of 0.65 and rated at 1000 B.T.U. per cubic foot. The natural gas supply connection(s) shall be not less than the size of the gas piping but shall be not smaller than 3/4 inch nominal pipe size.

Table to paragraph (d) - Maximum Capacity of Different Sizes of Pipe and Tubing in Thousands of Btu/hr of Natural Gas for Gas Pressures of 0.5 psig or Less, and a Maximum Pressure Drop of 1/2 in. Water Column

ID (in.) 10 ft 20 ft 30 ft 40 ft 50 ft 60 ft 70 ft 80 ft 90 ft 100 ft
Iron Pipe Sizes - Length
1/4 43 29 24 20 18 16 15 14 13 12
3/8 95 65 52 45 40 36 33 31 29 27
1/2 175 120 97 82 73 66 61 57 53 50
3/4 360 250 200 170 151 138 125 118 110 103
1 680 465 375 320 285 260 240 220 215 195
EHD 2 ID (in.) 10 ft 20 ft 30 ft 40 ft 50 ft 60 ft 70 ft 80 ft 90 ft 100 ft
Corrugated Stainless Steel Tubing - Length 1
13 3/8 31 21 17 14 13 12 11 10 10 9
15 3/8 42 30 24 20 18 16 15 14 13 12
18 1/2 79 56 45 39 36 33 30 28 27 25
19 1/2 91 64 52 45 40 36 35 32 31 29
23 3/4 155 111 92 80 72 65 60 58 55 52
25 3/4 184 132 108 93 84 77 71 66 62 60
30 1 317 222 180 156 138 126 116 108 103 97
31 1 368 258 209 180 161 147 135 127 120 113
37 1 1/4 598 426 350 304 273 250 231 217 205 195
OD (in.) 10 ft 20 ft 30 ft 40 ft 50 ft 60 ft 70 ft 80 ft 90 ft 100 ft
Copper Tubing - Length
1/4 27 18 15 13 11 10 9 9 8 8
3/8 56 38 31 26 23 21 19 18 17 16
1/2 113 78 62 53 47 43 39 37 34 33
3/4 197 136 109 93 83 75 69 64 60 57
1 280 193 155 132 117 106 98 91 85 81

1 Includes losses for four 90-degree bends and two end fittings. Tubing runs with larger numbers of bend and/or fittings shall be increased by an equivalent length of tubing according to the following equation: L = 1.3n, where L is actual length (ft) of tubing and n is the number of additional fittings and/or bends.

2 EHD (Equivalent Hydraulic Diameter) - A measure of the hydraulic efficiency between different tubing sizes.

(e) Joints for gas pipe. All pipe joints in the piping system, unless welded or brazed, shall be threaded joints that comply with Pipe Threads, General Purpose (Inch), adopted 25 October 1984, ANSI/ASME B1.20.1-1983. Right and left nipples or couplings shall not be used. Unions, if used, shall be of ground joint type. The material used for welding or brazing pipe connections shall have a melting temperature in excess of 1,000 F.

(f) Joints for tubing.

(1) Tubing joints shall be made with either a single or a double flare of 45 degrees in accordance with Flares For Tubing, SAE-J533b-1992 or with other listed vibration-resistant fittings, or joints may be brazed with material having a melting point exceeding 1,000 °F. Metallic ball sleeve compression-type tubing fittings shall not be used.

(2) Steel tubing joints shall be made with a double-flare in accordance with Flares For Tubing, SAE-J533b-1972.

(g) Pipe joint compound. Screw joints shall be made up tight with listed pipe joint compound, insoluble in liquefied petroleum gas, and shall be applied to the male threads only.

(h) Concealed tubing.

(1) Copper tubing must not be run inside walls, floors, partitions, or roofs. Corrugated stainless steel tubing (CSST) may be run inside walls, floors, partitions, and roofs under the following conditions:

(i) The CSST is protected from accidental puncture by a steel strike barrier not less than 0.058 inch thick, or the barrier's equivalent, installed between the tubing and the finished wall and extending 4 inches beyond concealed penetrations of plates, firestops, and wall studs, or specified by the tubing manufacturer's instructions; and

(ii) The CSST is installed in single runs and is not rigidly secured.

(2) Where tubing passes through exterior walls, floors, partitions, or similar construction, the tubing must be protected by the use of weather-resistant grommets that snugly fit both the tubing and the hole through which the tubing passes, or protected as specified in the tubing manufacturer's instructions.

(3) Concealed joints: Piping or tubing joints must not be located in any wall, floor, partition, or similar concealed construction space.

(i) Concealed joints. Piping or tubing joints shall not be located in any floor, wall partition, or similar concealed construction space.

(j) Gas supply connections. When gas appliances are installed, at least one gas supply connection must be provided on each home. The connection must not be located beneath an exit door. Where more than one connection is provided, the piping system must be sized to provide adequate capacity from each supply connection.

(k) Identification of gas supply connections. Each manufactured home must have permanently affixed to the exterior skin at or near each gas supply connection or the end of the pipe, a tag of 3 inches by 1 3/4 inches minimum size, made of etched, metal-stamped or embossed brass, stainless steel, anodized or alcalde aluminum not less than 0.020 inch thick, or other approved material [e.g., 0.005 inch plastic laminates], with the information shown in Figure 1 to this paragraph (k). The connector capacity indicated on this tag must be equal to or greater than the total Btu/hr rating of all intended gas appliances.

(l) LP-gas supply connectors.

(1) A listed LP-Gas flexible connection conforming to UL 569-1995, Pigtails and Flexible Hose Connectors for LP Gas, or equal must be supplied when LP-Gas cylinders(s) and regulator(s) are supplied.

(2) Appliance connections. All gas burning appliances shall be connected to the fuel piping. Materials as provided in § 3280.705(b) or listed appliance connectors shall be used. Listed appliance connectors when used shall not run through walls, floors, ceilings or partitions, except for cabinetry, and shall be 3 feet or less in length or 6 feet or less for cooking appliances. Connectors of aluminum shall not be used outdoors. A manufactured home containing a combination LP-natural-gas-system may be provided with a gas outlet to supply exterior appliances when installed in accordance with the following:

(i) No portion of the completed installation shall project beyond the wall of the manufactured home.

(ii) The outlet must be provided with an approved quick-disconnect device, which must be designed to provide a positive seal on the supply side of the gas system when the appliance is disconnected. A shutoff valve of the non-displaceable rotor type conforming to ANSI Z21.15-1997, Manually Operated Gas Valves, must be installed immediately upstream of the quick-disconnect device. The complete device must be provided as part of the original installation.

(iii) Protective caps or plugs for the “quick-disconnect” device, when disconnected, shall be permanently attached to the manufactured home adjacent to the device.

(iv) A tag shall be permanently attached to the outside of the exterior wall of the manufactured home as close as possible to the gas supply connection. The tag shall indicate the type of gas and the Btuh capacity of the outlet and shall be legibly inscribed as follows:


(3) Valves. A shutoff valve must be installed in the fuel piping at each appliance inside the manufactured home structure, upstream of the union or connector in addition to any valve on the appliance and so arranged to be accessible to permit servicing of the appliance and removal of its components. The shutoff valve must be located within 6 feet of any cooking appliance and within 3 feet of any other appliance. A shutoff valve may serve more than one appliance if located as required by this paragraph (3). The shutoff valve must be of the non-displaceable rotor type and conform to ANSI Z21.15-1997, Manually Operated Gas Valves.

(4) Gas piping system openings. All openings in the gas piping system shall be closed gas-tight with threaded pipe plugs or pipe caps.

(5) Electrical ground. Gas piping shall not be used for an electrical ground.

(6) Couplings. Pipe couplings and unions shall be used to join sections of threaded piping. Right and left nipples or couplings shall not be used.

(7) Hangers and supports. All horizontal gas piping must be adequately supported by galvanized or equivalently protected metal straps or hangers at intervals of not more than 4 feet, except where adequate support and protection is provided by structural members. Vertical gas piping in multi-story dwelling units must be supported at intervals of not more than 6 feet. Solid iron-pipe connection(s) must be rigidly anchored to a structural member within 6 inches of the supply connection(s).

(8) Testing for leakage.

(i) Before appliances are connected, piping systems must stand a pressure of three ± 0.2 psi gauge for a period of not less than ten minutes without showing any drop in pressure. Pressure must be measured with a mercury manometer or slope gauge calibrated so as to be read in increments of not greater than one-tenth pound, or an equivalent device. The source of normal operating pressure must be isolated before the pressure tests are made. Before a test is begun, the temperature of the ambient air and of the piping must be approximately the same, and constant air temperature must be maintained throughout the test.

(ii) After appliances are connected, the piping system shall be pressurized to not less than 10 inches nor more than 14 inches water column and the appliance connections tested for leakage with soapy water or bubble solution.

(iii) Where gas piping between transportable sections must be made on site, the installation instructions must contain provisions for onsite testing for leakage consistent with the provisions in paragraph (l)(8)(i) of this section.

[40 FR 58752, Dec. 18, 1975, as amended at 42 FR 54383, Oct. 5, 1977. Redesignated at 44 FR 20679, Apr. 6, 1979, as amended at 52 FR 4587, Feb. 12, 1987; 58 FR 55016, Oct. 25, 1993; 70 FR 72050, Nov. 30, 2005; 78 FR 73987, Dec. 9, 2013; 86 FR 2522, Jan. 12, 2021]

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