Sizing methods & openings

Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:

• CMC § 0.002 High relevance — show source text

  Each opening shall have a minimum free area of 1 square inch per 1000 Btu/h (0.002 m [2] /kW) of the total input rating of all appliances in the space, but not less than 100 square inches (0.065 m [2] ). One permanent opening shall commence within 12 inches (305 mm) of the top of the enclosure and one permanent opening shall commence within 12 inches (305 mm) of the bottom of the enclosure (see Figure 701.5). The minimum dimension of air openings shall not be less than 3 inches (76 mm). (2) Combining spaces in different stories. The volumes of spaces in different stories shall be considered as communicating spaces where such spaces are connected by one or more permanent openings in doors or floors having a total minimum free area of 2 square inches per 1000 Btu/h (0.004 m [2] /kw) of total input rating of all appliances. [NFPA 54:9.3.2.3] 701.6 Outdoor Combustion Air. Outdoor combustion air shall be provided through opening(s) to the outdoors in accor

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  COMBUSTION AIR

  dance with the methods in Section 701.6.1 or Section 701.6.2. The minimum dimension of air openings shall not be less than

  FIGURE 701.5

  ALL COMBUSTION AIR FROM ADJACENT INDOOR SPACES

  THROUGH INDOOR COMBUSTION AIR OPENINGS

  [NFPA 54: FIGURE A.9.3.2.3(1)]

  701.6.1 Two Permanent Openings Method. Two permanent openings, one commencing within 12 inches (305 mm) of the top of the enclosure and one commencing within 12 inches (305 mm) of the bottom of the enclosure, shall be provided. The openings shall communicate directly, or by ducts, with the outdoors or spaces that freely communicate with the outdoors as follows:

  (1) Where directly communicating with the outdoors or where communicating to the outdoors through vertical ducts, each opening shall have a minimum free area of 1 square inch per 4000 Btu/h (0.0005 m [2] /kW) of total input rating of all appliances in the enclosure.

  [See Figure 701.6.1(1) and Figure 701.6.1(2)] (2) Where communicating with the outdoors through horizontal ducts, each opening shall have a minimum free area of not less than 1 square inch per 2000 Btu/h (0.001 m [2] /kW) of total input rating of all appliances in the enclosure. [See Figure 701.6.1(3)] [NFPA 54:9.3.3.1] 701.6.2 One Permanent Opening Method. One permanent opening, commencing within 12 inches (305 mm) of the top of the enclosure, shall be provided. The appliance shall have clearances of at least 1 inch (25.4 mm) from the sides and back and 6 inches (152 mm) from the front of the appliance.

• CMC § 1314.2 Medium relevance — show source text

  Where gas of a different specific gravity is to be delivered, the serving gas supplier shall be permitted to be contacted for specific gravity conversion factors to use in sizing piping systems from the pipe sizing tables in this chapter. 1314.2 Volume. The hourly volume of gas required at each piping outlet shall be taken as not less than the maximum hourly rating as specified by the manufacturer of the appliance or appliances to be connected to each such outlet.

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  FUEL GAS PIPING

  1314.3 Gas Appliances. Where the gas appliances to be installed have not been definitely specified, Table 1308.3.1 shall be permitted to be used as a reference to estimate requirements of typical appliances. To obtain the cubic feet per hour (m [3] /h) of gas required, divide the input of the appliances by the average Btu (kW•h) heating value per cubic foot (m [3] ) of the gas. The average Btu (kW•h) per cubic foot (m [3] ) of the gas in the area of the installation shall be permitted to be obtained from the serving gas supplier. 1314.4 Size of Piping Outlets. The size of the supply piping outlet for a gas appliance shall be not less than [1] ⁄ 2 of an inch (15 mm). The size of a piping outlet for a mobile home shall be not less than [3] ⁄ 4 of an inch (20 mm).

  1315.0 Required Gas Piping Size. 1315.1 Pipe Sizing Methods. Where the pipe size is to be determined using any of the methods in Section 1315.1.1 through Section 1315.1.3, the diameter of each pipe segment shall be obtained from the pipe sizing tables in Section 1315.2 or from the sizing equations in Section 1315.3. [NFPA 54:6.1] 1315.1.1 Longest Length Method. The pipe size of each section of gas piping shall be determined using the longest length of piping from the point of delivery to the most remote outlet and the load of the section. [NFPA 54:6.1.1] 1315.1.2 Branch Length Method. Pipe shall be sized as follows:

  (1) Pipe size of each section of the longest pipe run from the point of delivery to the most remote outlet shall be determined using the longest run of piping and the load of the section.

  (2) The pipe size of each section of branch piping not previously sized shall be determined using the length of piping from the point of delivery to the most remote outlet in each branch and the load of the section. [NFPA 54:6.1.2] 1315.1.3 Hybrid Pressure. The pipe size for each section of higher pressure gas piping shall be determined using the longest length of piping from the point of delivery to the most remote line pressure regulator. The pipe size from the line pressure regulator to each outlet shall be determined using the length of piping from the regulator to the most remote outlet served by the regulator. [NFPA 54:6.1.3] **1315.2 Sizing of Gas Piping Systems.

• CMC § 0.79 Medium relevance — show source text

  Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.4.2] 802.6.2.3 Category II, Category III, and Cate- gory IV Appliances. The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturers’ instructions. The sizing of plastic pipe specified by the appliance manufacturer as a venting material for Category II, III, and IV appliances shall be in accordance with the appliance manufacturers’ instructions. [NFPA 54:12.7.4.3] 802.6.2.4 Sizing. Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods. [NFPA 54:12.7.4.4] 802.6.3 Gas Vents Serving Appliances on More than One Floor. Where a common vent is installed in a multistory installation to vent Category I appliances located on more than one floor level, the venting system shall be designed and installed in accordance with engineering methods.

  Crawl spaces, basements, and attics shall be considered as floor levels. [NFPA 54:12.7.5.1] 802.6.3.1 Occupiable Space. All appliances connected to the common vent shall be located in rooms separated from occupiable space. Each of these rooms shall have provisions for an adequate supply of combustion, ventilation, and dilution air that is not supplied from occupiable space. [NFPA 54:12.7.5.2] (See Figure 802.6.3.1) 802.6.3.2 Multistory Venting System. The size of the connectors and common segments of multistory venting systems for appliances listed for use with a Type B double-wall gas vent shall be in accordance with Table 803.2(1), provided all of the following apply: (1) The available total height ( H ) for each segment of a multistory venting system is the vertical distance between the level of the highest draft hood outlet or flue collar on that floor and the centerline of the next highest interconnection tee. (2) The size of the connector for a segment is determined from the appliance’s gas input rate and available connector rise and shall not be smaller

  than the draft hood outlet or flue collar size.

  (3) The size of the common vertical vent segment, and of the interconnection tee at the base of that segment, is based on the total appliance’s gas input rate entering that segment and its available total height. [NFPA 54:12.7.5.3]

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  CHIMNEYS AND VENTS

  FIGURE 802.6.3.1

  PLAN VIEW OF PRACTICAL SEPARATION METHOD

  FOR MULTISTORY GAS VENTING

  [NFPA 54: FIGURE A.12.7.5.2]

  802.6.4 Support of Gas Vents. Gas vents shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.7.6]

• CMC § 802.6.2 Medium relevance — show source text

  installation instructions.

  802.6.2 Size of Gas Vents. Venting systems shall be sized and constructed in accordance with Section 802.6.2.1 through Section 802.6.2.3 and the appliance manufacturer’s instructions. [NFPA 54:12.7.4] 802.6.2.1 Category I Appliances. The sizing of natural draft venting systems serving one or more listed appliances equipped with a draft hood or appliances listed for use with a Type B gas vent, installed in a single story of a building, shall be in accordance with one of the following: (1) The provisions of Section 803.0. (2) Vents serving fan-assisted combustion system appliances, or combinations of fan-assisted combustion system and draft hood-equipped appliances, shall be sized in accordance with Section 803.0 or other engineering methods. (3) For sizing an individual gas vent for a single, draft hood-equipped appliance, the effective area of the vent connector and the gas vent shall be not less than the area of the appliance draft hood outlet or greater than seven times the draft hood outlet area.

  (4) For sizing a gas vent connected to two appliances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area.

  (5) Engineering methods. [NFPA 54:12.7.4.1]

  802.6.2.2 Vent Offsets. Type B and Type L vents sized in accordance with Section 802.6.2.1(3) or Section 802.6.2.1(4) shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad) except that a vent system having not more than one 60 degree (1 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.4.2] 802.6.2.3 Category II, Category III, and Cate- gory IV Appliances. The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturers’ instructions. The sizing of plastic pipe specified by the appliance manufacturer as a venting material for Category II, III, and IV appliances shall be in accordance with the appliance manufacturers’ instructions. [NFPA 54:12.7.4.3] 802.6.2.4 Sizing. Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods. [NFPA 54:12.7.4.4] 802.6.3 Gas Vents Serving Appliances on More than One Floor. Where a common vent is installed in a multistory installation to vent Category I appliances located on more than one floor level, the venting system shall be designed and installed in accordance with engineering methods.

  Crawl spaces, basements, and attics shall be considered as floor levels. [NFPA 54:12.7.5.1] **802.6.3.1 Occupiable Space.

• CMC § 5.3.2.3 Medium relevance — show source text

  The total connected hourly load shall be used as the basis for piping sizing, assuming all appliances are operating at full capacity simultaneously. Exception: Sizing shall be permitted to be based upon established load diversity factors. [NFPA 54:5.3.2.3] 1308.3.2 Sizing Methods. Gas piping shall be sized in accordance with one of the following: (1) Pipe sizing tables or sizing equations in this chapter.

  (2) Sizing tables included in a listed piping system manufacturer’s installation instructions.

  (3) Engineering methods. [NFPA 54:5.3.3] 1308.3.3 Allowable Pressure Drop. The design pressure loss in a piping system from the point of delivery to the inlet connection of all appliances served shall be such that the supply pressure at each appliance inlet is greater than or equal to the minimum pressure required by the appliance. [NFPA 54:5.3.4] 1308.4 Acceptable Piping Materials and Joining Methods. Materials used for piping systems shall comply with the requirements of Section 1308.4.1 through Section 1308.4.4.2.3. {NFPA 54:5.5.1.1} 1308.4.1 Used Materials. Pipe, fittings, valves, or other materials shall not be used again unless they are free of foreign materials and have been ascertained to be adequate for the service intended. [NFPA 54:5.5.1.2] 1308.4.2 Metallic Pipe. Metallic pipe shall be in accordance with Section 1308.4.2.1 through Section 1308.4.2.4.

  1308.4.2.1 Cast Iron. Cast-iron pipe shall not be used. [NFPA 54:5.5.2.1] 1308.4.2.2 Steel, Stainless Steel, and Wrought-Iron. Steel, stainless steel, and wroughtiron pipe shall be at least Schedule 40 and shall comply with the dimensional standards of ASME B36.10M and one of the following: (1) ASTM A53 (2) ASTM A106 (3) ASTM A312 {NFPA 54:5.5.2.2}

  TABLE 1308.3.1

  APPROXIMATE GAS INPUT FOR TYPICAL APPLIANCES

  [NFPA 54: TABLE A.5.3.2.1]

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  FUEL GAS PIPING

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  1308.4.3 Metallic Tubing. Tubing shall not be used with gases corrosive to the tubing material. [NFPA 54:5.5.3.1] 1308.4.3.1 Steel Tubing. Steel tubing shall comply with ASTM A254. [NFPA 54:5.5.3.2] **1308.4.3.2 Stainless Steel Tubing.

• CMC § 701.4.2 Medium relevance — show source text

  I other

  Required Volume other ≥ [21 ft] ACH [3] 1000 Btu/h

  ( )

  (2) For fan-assisted appliances, calculate using the following Equation 701.4.2(2). [NFPA 54:9.3.2.2(2)]

  [Equation 701.4.2(2)]

  15 ft [3] I

  fan

  Required Volume fan ≥ ACH 1000 Btu/h

  ( )

  Where:

  I other = All appliances other than fan-assisted input (Btu/h) (kW) I = Fan-assisted appliance input (Btu/h) (kW) fan ACH = Air change per hour (percent of volume of space exchanged per hour, expressed as a decimal)

  Required Volume other ≥ [21 ft] [3]

  ACH

  (

  I other

  [21 ft] [3]

  ACH 1000 Btu/h

  ( )

  15 ft [3] Required Volume fan ≥ ACH

  (

  15 ft [3] I

  fan ACH 1000 Btu/h

  ( )

  For SI units: 1 cubic foot = 0.0283 m [3], 1000 British thermal units per

  hour = 0.293 kW

  (3) For purposes of these calculations, an infiltration rate greater than 0.60 ACH shall not be used in Equation 701.4.2(1) and Equation 701.4.2(2). [NFPA 54:9.3.2.2(3)]

  701.5 Indoor Opening Size and Location. Openings used to connect indoor spaces shall be sized and located in accordance with the following: (1) Combining spaces on the same story. Each opening shall have a minimum free area of 1 square inch per 1000 Btu/h (0.002 m [2] /kW) of the total input rating of all appliances in the space, but not less than 100 square inches (0.065 m [2] ). One permanent opening shall commence within 12 inches (305 mm) of the top of the enclosure and one permanent opening shall commence within 12 inches (305 mm) of the bottom of the enclosure (see Figure 701.5). The minimum dimension of air openings shall not be less than 3 inches (76 mm). (2) Combining spaces in different stories. The volumes of spaces in different stories shall be considered as communicating spaces where such spaces are connected by one or more permanent openings in doors or floors having a total minimum free area of 2 square inches per 1000 Btu/h (0.004 m [2] /kw) of total input rating of all appliances. [NFPA 54:9.3.2.3] 701.6 Outdoor Combustion Air. Outdoor combustion air shall be provided through opening(s) to the outdoors in accor

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  COMBUSTION AIR

  dance with the methods in Section 701.6.1 or Section 701.6.2. The minimum dimension of air openings shall not be less than

  FIGURE 701.5

  ALL COMBUSTION AIR FROM ADJACENT INDOOR SPACES

• CMC § 0.03 Medium relevance — show source text

  140 000 Btu/h = 47 in [2] (0.03 m [2] ) 3000 Btu/in [2]

  (6) Determine the minimum outdoor combustion air opening area:

  Outdoor opening area = 0.49 (from Step 4) x 47 in [2] (0.03 m [2] ) = 23 in [2 ] (0.01 m [2] )

  Section 701.7.3(3) requires the minimum dimension of the air opening should not be less than 3 inches (76 mm). [NFPA 54:I.1]

  3600 ft [3]

  = 0.51 7000 ft [3]

  »

  and is equal to the draft hood outlet diameter. A 4 inch (102 mm) vent connector is selected.

  Furnace Vent Connector Diameter. Using Table 803.2(1), Vent Connector Capacity, read down the total Vent Height (H) column to 30 feet (9144 mm), and read across the 3 feet (914 mm) Connector Rise (R) row to the first Btu/h rating in the FAN MAX column that is equal to or greater than the furnace input rating. The 100 000 Btu/h (29 kW) furnace in this example falls within this range, so a 4 inch (102 mm) connector is adequate.

  Chimney Liner Diameter. The total input to the common vent is 135 000 Btu/h (40 kW). Using the Common Vent Capacity portion of Table 803.2(1), read down the total Vent Height (H) column to 30 feet (9144 mm) and across this row to find the smallest vent diameter in the FAN + NAT column

  that has a Btu/h rating greater than 135 000 Btu/h (40 kW). The 4 inch (102 mm) common vent has a capacity of 138 000 Btu/h (40.4 kW). Reducing the maximum capacity by 20 percent results in a maximum capacity for a 4 inch (102 mm) corrugated liner of 110 000 Btu/h (32 kW), less than the total input of 135 000 Btu/h (40 kW). So a larger liner is needed. The 5 inch (127 mm) common vent capacity listed in Table 803.2(1) is 210 000 Btu/h (62 kW), and after reducing by 20 percent is 168 000 Btu/h (49.2 kW). Therefore, a 5 inch (127 mm) corrugated metal liner should be used in this example.

  Single Wall Connectors. Once it has been established that relining the chimney is necessary, Type B double-wall vent connectors are not specifically required. This example could be redone using Table 803.2(2) for single-wall vent connectors. For this case, the vent connector and liner diameters would be the same as found for Type B double-wall connectors. [NFPA 54:F.2.4]

  F 103.0 Example of Combination Indoor and Out- door Combustion Air Opening Design. Determine the required combination of indoor and outdoor combustion air opening sizes for the following appliance installation example.

  Example Installation: A fan-assisted furnace and a draft hoodequipped water heater with the following inputs are located in a 15 foot by 30 foot (4572 mm by 9144 mm) basement with an 8 foot (2438 mm) ceiling. No additional indoor spaces can be used to help meet the appliance combustion air needs.

• CMC § 9.3.7.1 Medium relevance — show source text

  Where the free area through a design of louver, grille, or screen is known, it shall be used in calculating the size opening required to provide the free area specified. Where the louver and grille design and free area are not known, it shall be assumed that wood louvers have 25 percent free area and metal louvers and grilles have 75 percent free area. Nonmotorized louvers and grilles shall be fixed in the open position. [NFPA 54:9.3.7.1]

  701.10.1 Minimum Screen Mesh Size. Screens shall not be smaller than [1] ⁄ 4 of an inch (6.4 mm) mesh. [NFPA 54:9.3.7.2]

  701.10.2 Motorized Louvers. Motorized louvers shall be interlocked with the appliance so they are proven in the full open position prior to main burner ignition and during main burner operation. Means shall be provided to prevent the main burner from igniting should the louver fail to open during burner startup and to shut down the main burner if the louvers close during burner operation.

  [NFPA 54:9.3.7.3]

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  COMBUSTION AIR

  701.11 Combustion Air Ducts. Combustion air ducts shall comply with the following [NFPA 54:9.3.8]:

  (1) Ducts shall be constructed of galvanized steel or a material having equivalent corrosion resistance, strength, and rigidity.

  Exception: Within dwellings units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than one fireblock is removed. [NFPA 54:9.3.8.1]

  (2) Ducts shall terminate in an unobstructed space, allowing free movement of combustion air to the appliances.

  [NFPA 54:9.3.8.2]

  (3) Ducts shall serve a single space. [NFPA 54:9.3.8.3]

  (4) Ducts shall not serve both upper and lower combustion air openings where both such openings are used. The separation between ducts serving upper and lower combustion air openings shall be maintained to the source of combustion air. [NFPA 54:9.3.8.4]

  (5) Ducts shall not be screened where terminating in an attic space. [NFPA 54:9.3.8.5]

  (6) Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air. [NFPA 54:9.3.8.6]

  (7) The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory built chimney shall not be used to supply combustion air.

  Exception: Direct vent appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:9.3.8.7]

  (8) Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located at least 12 inches (305 mm) vertically from the adjoining finished ground level.

• CMC § 9.3.4 Medium relevance — show source text

  [NFPA 54:9.3.4(3)] 701.8 Engineered Installations. Engineered combustion air installations shall provide an adequate supply of combustion, ventilation, and dilution air determined using engineering methods. [NFPA 54:9.3.5] 701.9 Mechanical Combustion Air Supply. Where all combustion air is provided by a mechanical air supply system, the combustion air shall be supplied from outdoors at the minimum rate of not less than 0.35 cubic feet per minute per 1000 Btu/h [0.034 (m [3] /min)/kW] for all appliances located within the space. [NFPA 54:9.3.6]

  701.9.1 Exhaust Fans. Where exhaust fans are installed, additional air shall be provided to replace the exhausted air. [NFPA 54:9.3.6.1]

  701.9.2 Interlock. Each of the appliances served shall be interlocked to the mechanical air supply system to prevent main burner operation where the mechanical air supply system is not in operation. [NFPA 54:9.3.6.2] 701.9.3 Specified Combustion Air. Where combustion air is provided by the building’s mechanical ventilation system, the system shall provide the specified combustion air rate in addition to the required ventilation air. [NFPA 54:9.3.6.3] 701.10 Louvers, Grilles, and Screens. The required size of openings for combustion, ventilation, and dilution air shall be based on the net free area of each opening. Where the free area through a design of louver, grille, or screen is known, it shall be used in calculating the size opening required to provide the free area specified. Where the louver and grille design and free area are not known, it shall be assumed that wood louvers have 25 percent free area and metal louvers and grilles have 75 percent free area. Nonmotorized louvers and grilles shall be fixed in the open position. [NFPA 54:9.3.7.1]

  701.10.1 Minimum Screen Mesh Size. Screens shall not be smaller than [1] ⁄ 4 of an inch (6.4 mm) mesh. [NFPA 54:9.3.7.2]

  701.10.2 Motorized Louvers. Motorized louvers shall be interlocked with the appliance so they are proven in the full open position prior to main burner ignition and during main burner operation. Means shall be provided to prevent the main burner from igniting should the louver fail to open during burner startup and to shut down the main burner if the louvers close during burner operation.

  [NFPA 54:9.3.7.3]

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  COMBUSTION AIR

  701.11 Combustion Air Ducts. Combustion air ducts shall comply with the following [NFPA 54:9.3.8]:

  (1) Ducts shall be constructed of galvanized steel or a material having equivalent corrosion resistance, strength, and rigidity.

• CMC § 101.0 Medium relevance — show source text

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  APPENDIX J

  COMBINATION OF INDOOR AND OUTDOOR COMBUSTION AND

  VENTILATION OPENING DESIGN

  The provisions contained in this appendix are not mandatory unless specifically adopted by a state agency, or referenced in the adopting ordinance.

  J 101.0 General.

  J 101.1 Applicability. This appendix provides general guidelines for the sizing of combination indoor and outdoor combustion and ventilation air openings. J 101.2 Example of Combination Indoor and Outdoor Combustion Air Opening Design. Determine the required combination of indoor and outdoor combustion air opening sizes for the following appliance installation example.

  Example Installation: A fan-assisted furnace and a drafthood-equipped water heater with the following inputs are located in a 15 foot by 30 foot (4572 mm by 9144 mm) basement with an 8 foot (2438 mm) ceiling. No additional indoor spaces can be used to help meet the appliance combustion air needs.

  Fan-Assisted Furnace Input: 100 000 British thermal units per hour (Btu/h) (29 kW)

  Draft Hood-Equipped Water Heater Input: 40 000 Btu/h (11.7 kW)

  Solution:

  (1) Determine the total available room volume. Appliance room volume:

  15 feet by 30 feet (4572 mm by 9144 mm) with an 8 foot (2438 mm) ceiling = 3600 cubic feet (101.94 m [3] )

  (2) Determine the total required volume. The standard method to determine combustion air is used to calculate the required volume. The combined input for the appliances located in the basement is calculated as follows:

  100 000 Btu/h (29 kW) + 40 000 Btu/h (11.7 kW) = 140 000 Btu/h (41 kW)

  The standard method requires that the required volume be determined based on 50 cubic feet per 1000 Btu/h (4.83 m [3] /kW). Using Table J 101.2, the required volume for a 140 000 Btu/h (41 kW) combined input is 7000 cubic feet (198.22 m [3] ).

  Conclusion: The indoor volume is insufficient to supply combustion air since the total of 3600 cubic feet (101.94 m [3] ) does not meet the required volume of 7000 cubic feet (198.22 m [3] ). Therefore, additional combustion air shall be provided from the outdoors.

  (3) Determine ratio of the available volume to the required

  volume:	Col2
  3600 cubic feet	= 0.51
  7000 cubic feet	7000 cubic feet

  (4) Determine the reduction factor to be used to reduce the full outdoor air opening size to the minimum required based on the ratio of indoor spaces:

  1.00 – 0.51 (from Step 3) = 0.49

  (5) Determine the single outdoor combustion air opening size as though all combustion air is to come from outdoors. In this example, the combustion air opening directly communicates with the outdoors:

• CMC § 9.3.2.3 Medium relevance — show source text

  THROUGH INDOOR COMBUSTION AIR OPENINGS

  [NFPA 54: FIGURE A.9.3.2.3(1)]

  701.6.1 Two Permanent Openings Method. Two permanent openings, one commencing within 12 inches (305 mm) of the top of the enclosure and one commencing within 12 inches (305 mm) of the bottom of the enclosure, shall be provided. The openings shall communicate directly, or by ducts, with the outdoors or spaces that freely communicate with the outdoors as follows:

  (1) Where directly communicating with the outdoors or where communicating to the outdoors through vertical ducts, each opening shall have a minimum free area of 1 square inch per 4000 Btu/h (0.0005 m [2] /kW) of total input rating of all appliances in the enclosure.

  [See Figure 701.6.1(1) and Figure 701.6.1(2)] (2) Where communicating with the outdoors through horizontal ducts, each opening shall have a minimum free area of not less than 1 square inch per 2000 Btu/h (0.001 m [2] /kW) of total input rating of all appliances in the enclosure. [See Figure 701.6.1(3)] [NFPA 54:9.3.3.1] 701.6.2 One Permanent Opening Method. One permanent opening, commencing within 12 inches (305 mm) of the top of the enclosure, shall be provided. The appliance shall have clearances of at least 1 inch (25.4 mm) from the sides and back and 6 inches (152 mm) from the front of the appliance. The opening shall directly communicate with the outdoors or shall communicate through a vertical or horizontal duct to the outdoors or spaces that freely communicate with the outdoors (see Figure 701.6.2) and shall have a minimum free area of the following: (1) One square inch per 3000 Btu/h (0.0007 m [2] /kW) of the total input rating of all appliances located in the enclosure.

  (2) Not less than the sum of the areas of all vent connectors in the space. [NFPA 54:9.3.3.2] 701.7 Combination Indoor and Outdoor Combustion Air. The use of a combination of indoor and outdoor com bustion air shall be in accordance with Section 701.7.1 through Section 701.7.3. [NFPA 54:9.3.4] (see Appendix F for example calculations)

  FIGURE 701.6.1(1) ALL COMBUSTION AIR FROM OUTDOORS – INLET

  AIR FROM VENTILATED CRAWL SPACE AND OUTLET AIR TO

  VENTILATED ATTIC

  [NFPA 54: FIGURE A.9.3.3.1(1)(a)]

  FIGURE 701.6.1(2)

  ALL COMBUSTION AIR FROM OUTDOORS

  THROUGH VENTILATED ATTIC

  [NFPA 54: FIGURE A.9.3.3.1(1)(b)]

  148 2025 CALIFORNIA MECHANICAL CODE

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  COMBUSTION AIR

• CMC § 1313.1 Medium relevance — show source text

  1313.1 Piping Installations . . . . . . . . . . . . 291

  1313.2 Test Preparation . . . . . . . . . . . . . . 292

  1313.3 Test Pressure . . . . . . . . . . . . . . . . 292

  1313.4 Detection of Leaks and Defects . . 292

  1313.5 Piping System Leak Test . . . . . . . 292

  1313.6 Purging Requirements . . . . . . . . . 292

  Table 1313.6.1 Size and Length of Piping. . . . . . . 293

  1314.0 Required Gas Supply . . . . . . . . . . 293

  1314.1 General. . . . . . . . . . . . . . . . . . . . . 293

  1314.2 Volume . . . . . . . . . . . . . . . . . . . . . 293

  1314.3 Gas Appliances . . . . . . . . . . . . . . 294

  1314.4 Size of Piping Outlets . . . . . . . . . . 294

  1315.0 Required Gas Piping Size . . . . . . 294

  1315.1 Pipe Sizing Methods. . . . . . . . . . . 294

  1315.2 Sizing of Gas Piping Systems . . . 294

  1315.3 Sizing Equations. . . . . . . . . . . . . . 294

  Table 1315.3 Cr and Y for Natural Gas and

  Undiluted Propane at Standard Conditions. . . . . . . . . . . . . . . . . . . 295

  1315.4 Sizing of Piping Sections . . . . . . . 295

  1315.5 Engineering Methods . . . . . . . . . . 295

  1315.6 Variable Gas Pressures . . . . . . . . 295

  Table 1315.2(1) Schedule 40 Metallic Pipe . . . . . . 297

  Table 1315.2(2) Schedule 40 Metallic Pipe . . . . . . 298

  Table 1315.2(3) Schedule 40 Metallic Pipe . . . . . . 299

  Table 1315.2(4) Schedule 40 Metallic Pipe . . . . . . 300

  Table 1315.2(5) Schedule 40 Metallic Pipe . . . . . . 301

  Table 1315.2(6) Schedule 40 Metallic Pipe . . . . . . 302

  Table 1315.2(7) Semi-Rigid Copper Tubing . . . . . . 303

  Table 1315.2(8) Semi-Rigid Copper Tubing . . . . . . 304

  Table 1315.2(9) Semi-Rigid Copper Tubing . . . . . . 305

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  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  TABLE OF CONTENTS

  Table 1315.2(10) Semi-Rigid Copper Tubing . . . . . . 306

  Table 1315.2(11) Semi-Rigid Copper Tubing . . . . . . 307

  Table 1315.2(12) Semi-Rigid Copper Tubing . . . . . . 308