Sizing Category I Venting Systems & Vent Connectors

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

• CMC § 802.1 High relevance — show source text

  802.1 Listing . . . . . . . . . . . . . . . . . . . . . . 153

  802.2 Connection to Venting Systems . . 153

  802.3 Minimum Safe Performance . . . . . 153

  802.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . . . . . . 154

  802.5 Masonry, Metal, and Factory-Built Chimneys . . . . . . . . . . . . . . . . . . . 154

  Table 802.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . . . . . . 155

  802.6 Gas Vents. . . . . . . . . . . . . . . . . . . 157

  Table 802.6.1 Roof Slope Heights. . . . . . . . . . . . 158

  802.7 Single-Wall Metal Pipe . . . . . . . . . 159

  Table 802.7.3.3 Clearance for Connectors. . . . . . . 160

  802.8 Through-the-Wall Vent Termination . . . . . . . . . . . . . . . . . . 160

  802.9 Condensation Drain . . . . . . . . . . . 160

  802.10 Vent Connectors for Category I Appliances . . . . . . . . . . . . . . . . . . 160

  Table 802.10.1.3 Minimum Thickness for Galvanized

  Steel Vent Connectors for Low Heat Appliances . . . . . . . . . . . . . . 161

  Table 802.10.1.4 Minimum Thickness for Steel

  Vent Connectors for Medium Heat Appliances . . . . . . . . . . . . . . 161

  Table 802.8.1 Through-the-Wall Direct Vent Termination Clearances . . . . . . . . 162

  802.11 Vent Connectors for Category II, Category III, and Category IV Appliances . . . . . . . . . . . . . . . . . . 164

  802.12 Appliances Requiring Draft Hoods . . . . . . . . . . . . . . . . . . 164

  802.13 Manually Operated Dampers . . . . 165

  802.14 Automatically Operated Vent Dampers . . . . . . . . . . . . . . . . . . . . 165

  802.15 Obstruction of Flow. . . . . . . . . . . . 165

  803.0 Sizing of Category I Venting Systems . . . . . . . . . . . . . . . . . . . . 165

  803.1 Additional Requirements to Single Appliance Vent . . . . . . . . . 165

  803.2 Additional Requirements to Multiple-Appliance Vent.. . . . . . . . 167

  Table 803.2.1 Vent Connector Maximum

  Length. . . . . . . . . . . . . . . . . . . . . . 167

  Table 803.1.2(1) Type B Double-Wall Gas Vent . . . 172

  Table 803.1.2(2) Type B Double-Wall Gas Vent . . . 175

• CMC § 802.10.1.4 High relevance — show source text

  Table 802.10.1.4 Minimum Thickness for Steel

  Vent Connectors for Medium Heat Appliances . . . . . . . . . . . . . . 161

  Table 802.8.1 Through-the-Wall Direct Vent Termination Clearances . . . . . . . . 162

  802.11 Vent Connectors for Category II, Category III, and Category IV Appliances . . . . . . . . . . . . . . . . . . 164

  802.12 Appliances Requiring Draft Hoods . . . . . . . . . . . . . . . . . . 164

  802.13 Manually Operated Dampers . . . . 165

  802.14 Automatically Operated Vent Dampers . . . . . . . . . . . . . . . . . . . . 165

  802.15 Obstruction of Flow. . . . . . . . . . . . 165

  803.0 Sizing of Category I Venting Systems . . . . . . . . . . . . . . . . . . . . 165

  803.1 Additional Requirements to Single Appliance Vent . . . . . . . . . 165

  803.2 Additional Requirements to Multiple-Appliance Vent.. . . . . . . . 167

  Table 803.2.1 Vent Connector Maximum

  Length. . . . . . . . . . . . . . . . . . . . . . 167

  Table 803.1.2(1) Type B Double-Wall Gas Vent . . . 172

  Table 803.1.2(2) Type B Double-Wall Gas Vent . . . 175

  Table 803.1.2(3) Masonry Chimney. . . . . . . . . . . . . 177

  Table 803.1.2(4) Masonry Chimney. . . . . . . . . . . . . 179

  Table 803.1.2(5) Single-Wall Metal Pipe or Type B Asbestos-Cement Vent. . . . . . . . . 181

  Table 803.1.2(6) Exterior Masonry Chimney . . . . . . 182

  2025 CALIFORNIA MECHANICAL CODE

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  TABLE OF CONTENTS

  Table 803.2(1) Type B Double-Wall Vent . . . . . . 183

  Table 803.2(2) Type B Double-Wall Vent . . . . . . . 187

  Table 803.2(3) Masonry Chimney. . . . . . . . . . . . . 189

  Table 803.2(4) Masonry Chimney. . . . . . . . . . . . . 191

  Table 803.2(5) Single-Wall Metal Pipe or Type B Asbestos-Cement Vent . . . 193

  Table 803.2(6) Exterior Masonry Chimney . . . . . . 193

  Table 803.2(7) Exterior Masonry Chimney . . . . . . 194

  Table 803.2(8) Exterior Masonry Chimney . . . . . . 195

  Table 803.2(9) Exterior Masonry Chimney . . . . . . 196

  CHAPTER 9 INSTALLATION OF

  SPECIFIC APPLIANCES. . . . . . . 197

• CMC § 101.0 High relevance — show source text

  2025 CALIFORNIA MECHANICAL CODE 533

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  APPENDIX F

  SIZING OF VENTING SYSTEMS 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.

  F 101.0 General.

  F 101.1 Applicability. This appendix provides general guidelines for sizing venting systems serving appliances equipped with draft hoods, Category I appliances, and appliances listed for use with Type B vents.

  Table 803.1.2(1) is used when sizing a Type B double-wall gas vent connected directly to the appliance.

  Note: The appliance can be either Category I draft hood-equipped or fanassisted type.

  FIGURE F 101.2(1) TYPE B DOUBLE-WALL VENT SYSTEM SERVING A SINGLE APPLIANCE WITH A TYPE B DOUBLE-WALL VENT

  [NFPA 54: FIGURE F.1(a)]

  Table 803.1.2(2) is used when sizing a single-wall metal vent connector attached to a Type B double-wall gas vent.

  Note: The appliance can be either Category I draft hood-equipped or fanassisted type.

  FIGURE F 101.2(2) TYPE B DOUBLE-WALL VENT SYSTEM SERVING A SINGLE APPLIANCE WITH A SINGLE-WALL METAL VENT CONNECTOR

  [NFPA 54: FIGURE F.1(b)]

  F 101.2 Examples Using Single Appliance Venting Tables. See Figure F 101.2(1) through Figure F 101.2(14).

  [NFPA 54:F.1]

  Table 803.1.2(3) is used when sizing a Type B double-wall gas vent connector attached to a tile-lined masonry chimney.

  Notes:

  1. A is the equivalent cross-sectional area of the tile liner.
  2. The appliance can be either Category I draft hood-equipped or fanassisted type.

  FIGURE F 101.2(3) VENT SYSTEM SERVING A SINGLE APPLIANCE WITH A MASONRY CHIMNEY AND A TYPE B DOUBLE-WALL VENT CONNECTOR

  [NFPA 54: FIGURE F.1(c)]

  Table 803.1.2(4) is used when sizing a single-wall vent connector attached to a tile-lined masonry chimney.

  Notes:

  1. A is the equivalent cross-sectional area of the tile liner.
  2. The appliance can be either Category I draft hood-equipped or fanassisted type.

  FIGURE F 101.2(4) VENT SYSTEM SERVING A SINGLE APPLIANCE USING A MASONRY CHIMNEY AND A SINGLE-WALL METAL VENT CONNECTOR

  [NFPA 54: FIGURE F.1(d)]

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  2025 CALIFORNIA MECHANICAL CODE 535

• CMC § 1.11.0. High relevance — show source text

  Adopting Agency	BSC	BSC- CG	SFM	HCD	Col6	Col7	DSA	Col9	Col10	OSHPD	Col12	Col13	Col14	Col15	Col16	Col17	BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
  Adopting Agency	BSC	BSC- CG	SFM	1	2	1-AC	AC	** SS**	** SS/CC**	1	1R	2	3	4	5	6	6	6	6	6	6	6	6	6
  Adopt Entire Chapter
  Adopt Entire Chapter as amended (amended sections listed below)
  Adopt only those sections that are listed below
  Chapter/Section

  This state agency does not adopt sections identified with the following symbol: † The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.

  2025 CALIFORNIA MECHANICAL CODE 533

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  534 2025 CALIFORNIA MECHANICAL CODE

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

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  APPENDIX F

  SIZING OF VENTING SYSTEMS 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.

  F 101.0 General.

  F 101.1 Applicability. This appendix provides general guidelines for sizing venting systems serving appliances equipped with draft hoods, Category I appliances, and appliances listed for use with Type B vents.

  Table 803.1.2(1) is used when sizing a Type B double-wall gas vent connected directly to the appliance.

  Note: The appliance can be either Category I draft hood-equipped or fanassisted type.

  FIGURE F 101.2(1) TYPE B DOUBLE-WALL VENT SYSTEM SERVING A SINGLE APPLIANCE WITH A TYPE B DOUBLE-WALL VENT

  [NFPA 54: FIGURE F.1(a)]

  Table 803.1.2(2) is used when sizing a single-wall metal vent connector attached to a Type B double-wall gas vent.

  Note: The appliance can be either Category I draft hood-equipped or fanassisted type.

• CMC § 802.6.2 High 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 § 509.1 High relevance — show source text

  509.1 Listing . . . . . . . . . . . . . . . . . . . . . . .91

  509.2 Connection to Venting Systems . . .91

  509.3 Minimum Safe Performance . . . . . .91

  509.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . . . .92

  Table 509.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . .92

  509.5 Masonry, Metal, and Factory-Built Chimneys . . . . . . . . .93

  509.6 Gas Vents . . . . . . . . . . . . . . . . . . . .94

  Table 509.6.1 Roof Slope Heights . . . . . . . . . . . .95

  509.7 Single-Wall Metal Pipe . . . . . . . . . .97

  Table 509.7.3.4(1) Clearances for Connectors . . . . . . .97

  Table 509.7.3.4(2) Reduction of Clearances with Specified Forms of Protection . . . .99

  509.8 Through-the-Wall Vent Termination . . . . . . . . . . . . . . . . . .100

  509.9 Condensation Drain . . . . . . . . . . .100

  509.10 Vent Connectors for

  Category I Appliances . . . . . . . . .100

  Table 509.8.1 Through-the-Wall Direct-Vent Termination Clearances . . . . . . . .101

  Table 509.10.1.3 Minimum Thickness for

  Galvanized Steel Vent

  Connectors for Low-Heat

  Appliances . . . . . . . . . . . . . . . . . .102

  Table 509.10.1.4 Minimum Thickness for Steel

  Vent Connectors for

  Medium-Heat Appliances . . . . . . .102

  509.11 Vent Connectors for

  Category II, Category III, and Category IV Appliances . . . . . . . .104

  509.12 Appliances Requiring Draft Hoods . . . . . . . . . . . . . . . . . . . . . .104

  509.13 Manually Operated Dampers . . . .104

  509.14 Automatically Operated Vent Dampers . . . . . . . . . . . . . . . .104

  509.15 Obstructions . . . . . . . . . . . . . . . . .104

  510.0 Sizing of Category I Venting Systems . . . . . . . . . . . . . . . . . . . .104

  510.1 Additional Requirements to Single Appliance Vent . . . . . . . . .104

  510.2 Additional Requirements to Multiple-Appliance Vent . . . . . . . . .106

  Table 510.2.1 Vent Connector Maximum

  Length . . . . . . . . . . . . . . . . . . . . . .106

  Table 510.1.2(1) Type B Double-Wall Gas Vent . . .110

  Table 510.1.2(2) Type B Double-Wall Gas Vent . . .113

  Table 510.1.2(3) Masonry Chimney . . . . . . . . . . . . .115

• CMC § 12.7.4.1 High relevance — show source text

  (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] 509.6.2.2 Vent Offsets. Type B and Type L vents sized in accordance with Section 509.6.2.1(3) or Section 509.6.2.1(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 (1.05 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] 509.6.2.3 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] 509.6.2.4 Sizing. Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods. [NFPA 54:12.7.4.4] 509.6.3 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]

  509.6.3.1 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 509.6.3.1)

  FIGURE 509.6.3.1

  PLAN VIEW OF PRACTICAL SEPARATION

  METHOD FOR MULTISTORY GAS VENTING

  [NFPA 54: FIGURE A.12.7.5.2]

  509.6.3.2 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 510.2(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.

• CMC § 0.79 High relevance — show source text

  (2) The connectors shall be attached to the vertical portion of the chimney or vent at an angle of 45 degrees (0.79 rad) or less relative to the vertical. [NFPA 54:12.11.4.1]

  509.10.3.1 Height of Connector. Where two or more vent connectors enter a common vent, chimney flue, or single-wall metal pipe, the smaller connector shall enter at the highest level consistent with the available headroom or clearance to combustible material. [NFPA 54:12.11.4.2]

  509.10.3.2 Pressure. Vent connectors serving Category I appliances shall not be connected to any portion of a mechanical draft system operating under positive static pressure, such as those serving Category III or Category IV appliances. [NFPA 54:12.11.4.3]

  509.10.4 Clearance. Minimum clearances from vent

  connectors to combustible material shall be in accordance with Table 509.7.3.4(1).

  Exception: The clearance between a vent connector and combustible material shall be permitted to be reduced where the combustible material is protected as specified for vent connectors in Table 509.7.3.4(2). [NFPA 54:12.11.5]

  509.10.5 Joints. Joints between sections of connector piping and connections to flue collars or draft hood outlets shall be fastened in accordance with one of the following methods:

  (1) Mechanically fastened by means of not less than three sheet-metal screws equally spaced around the joint.

  (2) Vent connectors of listed vent material assembled and connected to flue collars or draft hood outlets in

  accordance with the manufacturer’s instructions.

  (3) Other approved means. {NFPA 54:12.11.6}

  509.10.6 Connector Junctions. Where vent connectors are joined together, the connection shall be made with a manufactured tee or wye fitting. [NFPA 54:12.11.7]

  509.10.7 Slope. A vent connector shall be installed without any dips or sags and shall slope upward toward the vent or chimney at least [1] ⁄ 4 inch per foot (20.8 mm/m).

  Exception: Vent connectors attached to a mechanical draft system installed in accordance with appliance and the draft system manufacturers’ instructions. [NFPA 54:12.11.8]

  509.10.8 Length of Vent Connector. The length of vent connectors shall comply with Section 509.10.8.1 or Section 509.10.8.2.

  509.10.8.1 Single Wall Connector. The maximum horizontal length of a single-wall connector shall be 75 percent of the height of the chimney or vent, except for engineered systems. [NFPA 54:12.11.9.1] 509.10.8.2 Type B Double Wall Connector. The maximum horizontal length of a Type B double-wall connector shall be 100 percent of the height of the chimney or vent, except for engineered systems. The maximum length of an individual connector for a chimney or vent system serving multiple appliances, from the appliance outlet to the junction with the common vent or another connector, shall be 100 percent of the height of the chimney or vent.

  [NFPA 54:12.11.9.2]

• CMC § 1.11.0. High relevance — show source text

  This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.

  2025 CALIFORNIA PLUMBING CODE 423

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

  424 2025 CALIFORNIA PLUMBING CODE

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

  APPENDIX G

  SIZING OF VENTING SYSTEMS

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

  G 101.0 General.

  G 101.1 Applicability. This appendix provides general guidelines for sizing venting systems serving appliances equipped with draft hoods, Category I appliances, and appliances listed for use with Type B vents.

  Table 510.1.2(1) is used when sizing a Type B double-wall gas vent connected directly to the appliance.

  Note: The appliance can be either Category I draft hood-equipped or fanassisted type. FIGURE G 101.2(1) TYPE B DOUBLE-WALL VENT SYSTEM SERVING A SINGLE APPLIANCE WITH A TYPE B DOUBLE-WALL VENT

  [NFPA 54: FIGURE F.1(a)]

  Table 510.1.2(2) is used when sizing a single-wall metal vent connector attached to a Type B double-wall gas vent.

  Note: The appliance can be either Category I draft hood-equipped or fanassisted type. FIGURE G 101.2(2) TYPE B DOUBLE-WALL VENT SYSTEM SERVING A SINGLE APPLIANCE WITH A SINGLE-WALL METAL VENT CONNECTOR

  [NFPA 54: FIGURE F.1(b)]

  G 101.2 Examples Using Single Appliance Venting Tables. See Figure G 101.2(1) through Figure G 101.2(14).

  [NFPA 54:F.1]

  Table 510.1.2(3) is used when sizing a Type B double-wall gas vent connector attached to a tile-lined masonry chimney.

  Notes:

  1. A is the equivalent cross-sectional area of the tile liner.
  2. The appliance can be either Category I draft hood-equipped or fan-assisted type. FIGURE G 101.2(3) VENT SYSTEM SERVING A SINGLE APPLIANCE WITH A MASONRY CHIMNEY AND A TYPE B DOUBLE-WALL VENT CONNECTOR

  [NFPA 54: FIGURE F.1(c)]

  Table 510.1.2(4) is used when sizing a single-wall vent connector attached to a tile-lined masonry chimney.

  Notes:

  1. A is the equivalent cross-sectional area of the tile liner.
  2. The appliance can be either Category I draft hood-equipped or fan-assisted type. FIGURE G 101.2(4) VENT SYSTEM SERVING A SINGLE APPLIANCE USING A MASONRY CHIMNEY AND A SINGLE-WALL METAL VENT CONNECTOR

  [NFPA 54: FIGURE F.1(d)]

• CMC § 509.10.1.3 High relevance — show source text

  Table 509.10.1.3 Minimum Thickness for

  Galvanized Steel Vent

  Connectors for Low-Heat

  Appliances . . . . . . . . . . . . . . . . . .102

  Table 509.10.1.4 Minimum Thickness for Steel

  Vent Connectors for

  Medium-Heat Appliances . . . . . . .102

  509.11 Vent Connectors for

  Category II, Category III, and Category IV Appliances . . . . . . . .104

  509.12 Appliances Requiring Draft Hoods . . . . . . . . . . . . . . . . . . . . . .104

  509.13 Manually Operated Dampers . . . .104

  509.14 Automatically Operated Vent Dampers . . . . . . . . . . . . . . . .104

  509.15 Obstructions . . . . . . . . . . . . . . . . .104

  510.0 Sizing of Category I Venting Systems . . . . . . . . . . . . . . . . . . . .104

  510.1 Additional Requirements to Single Appliance Vent . . . . . . . . .104

  510.2 Additional Requirements to Multiple-Appliance Vent . . . . . . . . .106

  Table 510.2.1 Vent Connector Maximum

  Length . . . . . . . . . . . . . . . . . . . . . .106

  Table 510.1.2(1) Type B Double-Wall Gas Vent . . .110

  Table 510.1.2(2) Type B Double-Wall Gas Vent . . .113

  Table 510.1.2(3) Masonry Chimney . . . . . . . . . . . . .115

  Table 510.1.2(4) Masonry Chimney . . . . . . . . . . . . .117

  Table 510.1.2(5) Single-Wall Metal Pipe or Type B Asbestos-Cement Vent . . .119

  Table 510.1.2(6) Exterior Masonry Chimney . . . . . .120

  Table 510.2(1) Type B Double-Wall Vent . . . . . . .121

  Table 510.2(2) Type B Double-Wall Vent . . . . . . .125

  Table 510.2(3) Masonry Chimney . . . . . . . . . . . . .127

  Table 510.2(4) Masonry Chimney . . . . . . . . . . . . .129

  Table 510.2(5) Single-Wall Metal Pipe or Type B Asbestos-Cement Vent . .131

  Table 510.2(6) Exterior Masonry Chimney . . . . . .131

  Table 510.2(7) Exterior Masonry Chimney . . . . . .132

  Table 510.2(8) Exterior Masonry Chimney . . . . . .133

  Table 510.2(9) Exterior Masonry Chimney . . . . . .134

  CHAPTER 6 WATER SUPPLY AND

  DISTRIBUTION . . . . . . . . . . . . . .135

  601.0 General . . . . . . . . . . . . . . . . . . . . .137

  601.1 Applicability . . . . . . . . . . . . . . . . . .137

  601.2 Water Supply and Flushing . . . . .137

• CMC § 2025 Medium relevance — show source text

  Chapter 7 Combustion Air. Chapter 7 regulates combustion air requirements for ventilation and dilution of flue gases for appliances installed in buildings. Fuel-gas appliances not regulated by chapter include direct vent appliances and Type I clothes dryers. Makeup air requirements for Type I clothes dryers are located in Chapter 5. Chapter 7 provides acceptable methods for supplying satisfactory combustion air to ensure proper combustion. Combustion air can be supplied by using indoor combustion air or by introducing the air from the outdoors.

  Combustion is the rapid oxidation of fuel to release energy. The oxygen required to release the energy from the fuel normally comes from the air. Incomplete combustion of fuel occurs when inadequate oxygen is provided to the appliance. Combustion is needed to provide ventilation cooling for the casing and internal controls. When a lack of oxygen occurs, some of the carbon is not oxidized, and carbon monoxide forms.

  Chapter 8 Chimneys and Vents. Chapter 8 regulates the installation, design, and construction of venting systems for fuel-burning appliances. The provisions addressed within this chapter follow procedures an installer would use to design or evaluate a venting system. Many requirements apply to the design and construction of venting systems, chimneys, installation of gas vents, and the sizing of venting system for a Category I appliance. Sizing venting systems require rigorous engineering calculations. However, the venting sizing requirements and sizing tables in this chapter already perform the calculations for the benefit of the end user.

  Combustion appliances produce products of incomplete combustion, including potentially harmful carbon monoxide (CO). It is desirable to vent these products to the outdoors. Although the gas is clean-burning fuel, the products of combustion must not be allowed to collect within a building.

  Chapter 9 Installation of Specific Appliances. Chapter 9 regulates the minimum requirements for the design, construction and installation of specific appliances. The provisions address the minimum requirements for gas-fired appliances, oil-fired appliances, wood-fired appliances, and electric-type appliances. In addition to the requirements of this chapter, appliances are also required to comply with the general requirements of Chapter 3.

  Chapter 10 Boilers and Pressure Vessels. Chapter 10 regulates the construction, installation, operation, repair, and alteration of boilers and pressure vessels. The safety provisions within this chapter address controls and limit devices for automatic boilers, methods of determining expansion tank capacities, discharge piping, relief valves, shutoff valves, gas-pressure and combustion regulators, and inspections and tests. Potable water heaters are free from the requirements of Chapter 10 as they are within the scope of the Uniform Plumbing Code (UPC).

  Pressure vessels store large amounts of energy and must comply with ASME Boiler and Pressure Vessel Code (BPVC) Section VIII.1. The stored energy must be contained to prevent disastrous failures. Boilers must comply with ASME BPVC Section I, ASME BPVC Section IV, or NFPA 85. Installing a safety relief valve and expansion tank prevents pressures in the tank from exceeding the design threshold.

  Chapter 11 Refrigeration. Chapter 11 regulates the design, installation, and construction requirements of refrigeration systems and the installation and construction of cooling towers. Refrigeration is a method used for achieving heat transfer to cool spaces. Refrigerants are the most common medium used to transfer the heat energy from the low-temperature level to the high-temperature level. Table

  2025 CALIFORNIA MECHANICAL CODE xv

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  FORMAT OF THE UNIFORM MECHANICAL CODE

• CMC § 223.0 Medium relevance — show source text

  223.0 – U –

  UMC. [HCD 1, HCD 2, OSHPD 1, 1R, 2, 3, 4, 5 & 6] The most recent edition of Uniform Mechanical Code published by the International Association of Plumbing and Mechanical Officials.

  Unconditioned Space. An area, room, or space not being heated or cooled by any equipment.

  Unit Heater. A heating appliance designed for nonresidential space heating and equipped with an integral means for circulation of air.

  46 2025 CALIFORNIA MECHANICAL CODE

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  DEFINITIONS

  Vented Appliance Categories. Category I. An appliance that operates with a nonpositive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent.

  [NFPA 54:3.3.4.10.1] Category II. An appliance that operates with a nonpositive vent static pressure and with a vent gas temperature that can cause excessive condensate production in the vent. [NFPA 54:3.3.4.10.2] Category III. An appliance that operates with a positive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent.

  [NFPA 54:3.3.4.10.3] Category IV. An appliance that operates with a positive vent static pressure and with a vent gas temperature that can cause excessive condensate production in the vent.

  [NFPA 54:3.3.4.10.4] Vented Decorative Appliance. A vented appliance whose only function is providing an aesthetic effect of flames. Vented Wall Furnace. A self-contained, vented, fuel gasburning appliance complete with grilles or equivalent, designed for incorporation in or permanent attachment to the structure of a building and furnishing heated air, circulated by gravity or by a fan, directly into the space to be heated through openings in the casing. [NFPA 54:3.3.45.7] Ventilating Ceiling. A suspended ceiling containing many small apertures through which air, at low pressure, is forced downward from an overhead plenum dimensioned by the concealed space between the suspended ceiling and the floor or roof above.

  Ventilation System. All of that equipment intended or installed for the purpose of supplying air to or removing air from, any room or space by mechanical means, other than equipment that is a portion of an environmental heating, cooling, absorption, or evaporative cooling system. Venting Collar. The outlet opening of an appliance provided for connection of the vent system. Venting System. The vent or chimney and its connectors, assembled to form a continuous open passageway from an appliance to the outdoors for the purpose of removing products of combustion. This definition also shall include a venting assembly that is an integral part of an appliance. Venting System, Gravity-Type. A system that depends entirely on the heat from the fuel being used to provide the energy required to vent an appliance. Venting System, Power-Type. A system that depends on a mechanical device to provide a positive draft within the venting system. **Volume, Internal Gross.