CMC · California Mechanical Code
How must gas vents be supported and spaced?
The California Mechanical Code (§ 802.6.4) requires that gas vents be supported and spaced exactly as the vent manufacturer’s listed installation instructions specify — the code itself gives no numeric spacing values, so installers must use the vent product’s manufacturer instructions and listings.
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
The California Mechanical Code says the installer must follow the manufacturer’s installation instructions for how a gas vent is supported and how far supports are spaced — there are no numeric support intervals stated in the section itself. The controlling provision is § 802.6.4.
The single most important rule: follow the vent or chimney manufacturer's listed installation instructions for support type and spacing — the CMC defers to the listing.
Requirements in detail
The plain code requirement
- The CMC text is concise: Gas vents shall be supported and spaced in accordance with the manufacturer’s installation instructions. This is stated in § 802.6.4.
- Where the code discusses other related venting items (chimneys, factory-built systems) it repeats the same approach: support and spacing follow the manufacturer’s listing/installation instructions. See § 802.5.9 for chimneys.
What the CMC does not specify
- § 802.6.4 does not provide numeric hanger spacing, bracket sizes, or specific support details for different vent diameters or vent types — it defers that to the vent manufacturer and the product listing. If you need numeric intervals, consult the listed vent product’s installation instructions or the vent manufacturer’s published tables; those numbers are not in § 802.6.4.
Decision‑relevant dimensions / values (what code tells you to check)
| Decision item | Typical place to get the value | Code Reference |
|---|---|---|
| Support type (e.g., wall bracket, roof support, clevis) | Manufacturer’s installation instructions / product listing | § 802.6.4 |
| Maximum spacing between supports (horizontal or vertical) | Manufacturer’s installation instructions / product listing | § 802.6.4 |
| Support for factory‑built chimneys (structural supports for weight) | Manufacturer’s installation instructions / listing | § 802.5.9 |
| When vent passes through insulated assemblies (shielding) | See insulation protection requirement in vent termination/install rules | § 802.6.1.1 |
Typical items you should verify on the manufacturer’s instructions
- Required hanger/bracket type and whether fasteners may penetrate inner walls of double‑wall vents (the CMC elsewhere forbids penetrating inner wall except at transition). Check the product instructions.
- Whether vertical runs require support at every floor level, or different spacing. The CMC references such practices for piping risers (see § 1310.3.5 and its Table), but gas vent spacing itself is governed by the vent manufacturer's listing.
Exceptions & special cases
- When a gas vent is installed inside a masonry chimney, the CMC still requires the installation to follow the vent manufacturer’s instructions; the vent must be permanently identified where it enters the chimney (labeling requirement in § 802.6). The support method for the vent inside the chimney should be per the vent listing.
- Factory‑built chimneys: all portions must be supported for design and weight, and listed factory‑built chimneys are to be supported and spaced per the manufacturer’s instructions (see § 802.5.9).
- Fasteners: the CMC indicates screws, rivets, and fasteners must not penetrate the inner wall of double‑wall gas vents except at the appliance transition; follow manufacture guidance for permitted fastener locations.
- The code does not exempt multistory common vents; multistory vent sizing and design have their own rules (e.g., § 802.6.3), but support/spacing for those vents is still per the manufacturer’s listing unless an engineered design is required.
Common mistakes
- Assuming the piping‑hanger spacing tables (for gas piping) apply to gas vents. They do not; vent support spacing is governed by the vent manufacturer (see § 802.6.4), while gas piping support spacing appears in the piping sections (e.g., § 1310.3.5 and Table 1310.3.5.1).
- Penetrating the inner wall of double‑wall vents with screws or rivets — the CMC forbids that except at the transition to the appliance. Verify permitted fasteners in the manufacturer instructions.
- Not retaining the vent manufacturer’s instructions or failing to show the installed system matches the listing during inspection — the code’s direction to follow the manufacturer requires the installer to be able to produce or follow those instructions.
- Treating chimney support and vent support as identical without checking listings — factory‑built chimneys have their own listed support requirements.
Worked example — how to apply § 802.6.4 (illustrative process)
The text of § 802.6.4 tells you to use the manufacturer’s instructions; those instructions provide the numbers. The CMC does not publish the spacing numbers, so the correct workflow is:
- Identify the vent product and listing (example: “Type B double‑wall listed X vent, 6‑inch nominal”). (This identification step — vent type and listing — is required by code language that repeatedly refers to listed vents.)
- Retrieve the manufacturer’s installation instructions / listing sheet for that exact product and diameter. (These documents typically state hanger types and maximum spacing — but those numeric values are in the manufacturer sheet, not in the CMC.)
- Follow the manufacturer’s spacing table exactly. Example (this example spacing is an illustrative, hypothetical manufacturer value — it is NOT from the CMC):
- Manufacturer sheet says: support horizontal vent runs every 3 ft and vertical runs with support brackets every 8 ft (or at each floor level), using listed wall brackets. Then install supports at these spacings and record the manufacturer sheet on the job.
- Because these numbers are taken from the product instructions, they satisfy the CMC requirement in § 802.6.4.
Important: the numeric values above are an illustrative example only. § 802.6.4 itself contains no spacing numbers — you must use the numbers printed on the vent manufacturer’s installation instructions or product listing.
Related provisions
- § 802.6 — Gas vents: general installation rules and listed‑vent requirements.
- § 802.6.1 — Gas vent termination and related shielding through insulation (insulation protection shield).
- § 802.5.9 — Support of chimneys; factory‑built chimneys supported per manufacturer.
- § 802.6.3 — Gas vents serving appliances on more than one floor (multistory venting).
- § 1310.3.5 and Table 1310.3.5.1 — Hangers, supports, and spacing rules for gas piping (useful to contrast piping rules with vent rules).
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 803.2 High relevance — show source text
** 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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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]
802.6.5 Marking. In those localities where solid and liquid fuels are used extensively, gas vents shall be permanently identified by a label attached to the wall or ceiling at a point where the vent connector enters the gas vent. The label shall read: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel-burning appliances or incinerators.” The Authority Having Jurisdiction shall determine whether its area constitutes such a locality. [NFPA 54:12.7.7] 802.7 Single-Wall Metal Pipe. Single-wall metal pipe shall be constructed of galvanized sheet steel not less than 0.0304 of an inch (0.7722 mm) thick or of other approved, noncombustible, corrosion-resistant material. [NFPA 54:12.8.1]
802.7.1 Cold Climate. Uninsulated single-wall metal pipe shall not be used outdoors for venting appliances in regions where the 99 percent winter design temperature is below 32°F (0°C). [NFPA 54:12.8.2]
802.7.2 Termination. The termination of single-wall metal pipe shall meet the following requirements:
(1) Single-wall metal pipe shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood outlet or flue collar.
(2) Single-wall metal pipe shall extend at least 2 feet (610 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm).
(3) An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe. [NFPA 54:12.8.3]
CMC § 0.8 High relevance — show source text
(a) NTS-1 and smaller shall be supported every 0.8 m (32 in), unless continuously supported by metallic CTS or V channels that (i) are supported at intervals not exceeding 1.8 m (6 ft); (ii) have a maximum cantilever, measured from the support to the end of the CTS support channel, of 0.5 m (1.5 ft); and (b) NTS-1-1/4 and larger shall be supported every 1.2 m (4 ft), unless continuously supported by metallic CTS or V channels that (i) are supported at intervals not exceeding 2.4 m (8 ft); and (ii) have a maximum cantilever, measured from the support to the end of the CTS support channel, of 0.5 m (1.5 ft). 7.3 Anchors
Anchors shall be
(a) used to restrict PEX tubing movement; (b) made of materials that provide rigidity to the support system and utilize pipe clamps designed for plastic tubing capable of restraining the tubing; and (c) installed in accordance with Figures 1 or 2, as applicable (i.e., anchor distances and size of arms and offsets). Note: Anchors are typically installed every 20 m (65 ft). See Section 6.
8 Joints and Connections
8.1 Assembly Procedure
The procedure for making joints shall be as specified by the manufacturer.
8.2 Concealed Joints
PEX tubing systems manufactured in accordance with the applicable standards referenced in Section 2 are deemed manufactured joints and may be installed in concealed spaces without the need for access panels.
9 Clearances
9.1 Gas Vents
Except for double-wall B-vents, which require a 25 mm (1 in) clearance, the clearance between gas appliance vents and PEX tubing shall be at least 150 mm (6 in). 9.2 Recessed Light Fixtures
Except when the PEX tubing is protected with fiberglass or closed-cell insulation or the recessed light is IC-rated, the clearance between recessed light fixtures and PEX tubing shall be at least 300 mm (12 in). 9.3 Fluorescent Lighting
When in direct view of the light source, the clearance between fluorescent lighting and PEX tubing shall be at least 1.5 m (5 ft). If the minimum clearance cannot be achieved, the PEX tubing shall be protected with a UV-blocking sleeve.
10 Other Considerations
10.1 Hot-Work Joints
Hot-work joints (e.g., soldering, brazing, welding, and fusion-welding) shall be
(a) made at least 500 mm (18 in) from PEX tubing in the same water line; and (b) performed prior to completing the PEX joints. 10.2 Bending Radius 10.2.1 The free (unsupported) bending radius for PEX tubing, measured at the outside of the bend, shall be not less than six times the actual outside diameter of the tubing, unless otherwise specified by the PEX manufacturer. Supports should be used to facilitate rigid bends and to alleviate stress on PEX joints when bends are needed in close proximity to such joints. 10.2.2 Tighter bends may be used when the PEX tubing is uniformly bent (supported) around a curved bracket or other rigid fixture.
CMC § 0.79 High 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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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 § 12.7.5.3 High relevance — show source text
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]
509.6.4 Support of Gas Vents. Gas vents shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.7.6]
509.6.5 Marking. In those localities where solid and liquid fuels are used extensively, gas vents shall be per
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WATER HEATERS
manently identified by a label attached to the wall or ceiling at a point where the vent connector enters the gas vent. The label shall read: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel-burning appliances or incinerators.” The Authority Having Jurisdiction shall determine whether its area constitutes such a locality. [NFPA 54:12.7.7] 509.7 Single-Wall Metal Pipe. Single-wall metal pipe shall be constructed of galvanized sheet steel not less than 0.0304 of an inch (0.7722 mm) thick or of other approved, noncombustible, corrosion-resistant material. [NFPA 54:12.8.1]
509.7.1 Cold Climate. Uninsulated single-wall metal pipe shall not be used outdoors for venting appliances in regions where the 99 percent winter design temperature is below 32°F (0°C). [NFPA 54:12.8.2]
509.7.2 Termination. The termination of single-wall metal pipe shall meet the following requirements:
(1) Single-wall metal pipe shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood outlet or flue collar.
[NFPA 54:12.8.3(1)]
(2) Single-wall metal pipe shall extend at least 2 feet (610 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm). [NFPA 54:12.8.3(2)]
(3) An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe. [NFPA 54:12.8.3(3)]
509.7.3 Installation with Appliances Permitted by Section 509.4. Single-wall metal pipe shall not be used as a vent in dwellings and residential occupancies.
[NFPA 54:12.8.4.1]
509.7.3.1 Limitations. Single-wall metal pipe shall be used only for runs directly from the space in
which the appliance is located through the roof or exterior wall to the outer air. A pipe passing through a roof shall extend without interruption through the roof flashing, roof jacket, or roof thimble. [NFPA 54:12.8.4.2]
CMC § 12.7.4.4 High relevance — show source text
[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.
(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]
509.6.4 Support of Gas Vents. Gas vents shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.7.6]
509.6.5 Marking. In those localities where solid and liquid fuels are used extensively, gas vents shall be per
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WATER HEATERS
manently identified by a label attached to the wall or ceiling at a point where the vent connector enters the gas vent. The label shall read: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel-burning appliances or incinerators.” The Authority Having Jurisdiction shall determine whether its area constitutes such a locality. [NFPA 54:12.7.7] 509.7 Single-Wall Metal Pipe. Single-wall metal pipe shall be constructed of galvanized sheet steel not less than 0.0304 of an inch (0.7722 mm) thick or of other approved, noncombustible, corrosion-resistant material. [NFPA 54:12.8.1]
CMC § 12.6.5.3 High relevance — show source text
The chimney flue shall be sized to properly vent the appliance.
[NFPA 54:12.6.5.3] 802.5.8.3 Combination Gas- and Oil-Burning Appliances. A single chimney flue serving a listed combination gas- and oil-burning appliance shall be sized in accordance with the appliance manufacturer’s instructions. [NFPA 54:12.6.5.4]
802.5.9 Support of Chimneys. All portions of chimneys shall be supported for the design and weight of the materials employed. Listed factory-built chimneys shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.6]
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CHIMNEYS AND VENTS
802.5.10 Cleanouts. Where a chimney that formerly carried flue products from liquid or solid fuel-burning appliances is used with an appliance using fuel gas, an accessible cleanout shall be provided. The cleanout shall have a tight-fitting cover and be installed so its upper edge is at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening. [NFPA 54:12.6.7] 802.5.11 Space Surrounding Lining or Vent. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appli ance.
Exception: The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer’s instructions. [NFPA 54:12.6.8.1] 802.5.11.1 Combustion Air. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal or factory-built chimney flue 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 54:12.6.8.2] 802.6 Gas Vents. The installation of gas vents shall meet the following requirements:
(1) Gas vents shall be installed in accordance with the manufacturer’s installation instructions.
(2) A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is
connected.
(3) Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel–burning appliances or incinerators.”
(4) Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent.
[NFPA 54:12.7.2] 802.6.1 Gas Vent Termination. The termination of gas vents shall comply with the following requirements:
(1) A gas vent shall terminate in accordance with one of the following:
CMC § 802.2.6 High relevance — show source text
(3) A Type B-W gas vent shall terminate at least 12 feet (3658 mm) in vertical height above the bottom of the wall furnace.
(4) A gas vent extending through an exterior wall shall not terminate adjacent to the wall or below eaves or parapets, except as provided in Section 802.2.6 and Section 802.3.3 through Section 802.3.3.4.
(5) Decorative shrouds shall not be installed at the termination of gas vents except where such shrouds are listed for use with the specific gas venting system and are installed in accordance with the manufac turer’s installation instructions.
(6) All gas vents shall extend through the roof flashing, roof jack, or roof thimble and terminate with a listed cap or listed roof assembly.
(7) A gas vent shall terminate at least 3 feet (914 mm) above a forced air inlet located within 10 feet (3048 mm). [NFPA 54:12.7.3]
FIGURE 802.6.1
TERMINATION LOCATIONS FOR
GAS VENTS WITH LISTED CAPS 12 INCHES OR LESS IN
SIZE NOT LESS THAN 8 FEET FROM A VERTICAL WALL
[NFPA 54: FIGURE 12.7.3]
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CHIMNEYS AND VENTS
TABLE 802.6.1
ROOF SLOPE HEIGHTS
[NFPA 54: TABLE 12.7.3]
ROOF SLOPE H (minimum) (feet)
Flat to6⁄121.0
Over6⁄12 to7⁄121.25
Over7⁄12 to8⁄121.5
Over8⁄12 to9⁄122.0
Over9⁄12 to10⁄122.5
Over10⁄12 to11⁄123.25 Over11⁄12 to12⁄12 4.0
Over12⁄12 to14⁄125.0
Over14⁄12 to16⁄126.0
Over16⁄12 to18⁄127.0
Over18⁄12 to20⁄127.5
Over20⁄12 to21⁄128.0 For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
802.6.1.1 Insulation Protection Shield. Where a vent passes through an insulated assembly, an approved metal shield constructed of steel having a thickness of not less than 0.0179 inch (0.45 mm) (26 gauge) shall be installed between the vent and insulation. The shield shall extend not less than 2 inches (51 mm) above the insulation and be secured to the structure in accordance with the manufacturer’s
installation instructions.
**802.6.2 Size of Gas Vents.
California Mechanical Code High relevance — show source text
|100 psf|1 hr
23 min|||7|1, 2|11/3| |F/C-4-RC-9|4″|4″ deep (4370 psi);1/4″ reinforcement bars
at 6″ pitch with3/4″ cover;1/4″ main rein-
forcement bars at 4″ pitch perpendicular
with1/2″ cover; 13′1″ span restrained.|150 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-10|4″|4″ thick (5140 psi) deck;1/4″ reinforce-
ment bars at 71/2″ pitch with7/8″ cover;3/8″
main reinforcement bars at 33/4″ pitch
perpendicular with1/2″ cover; 13′1″ span
restrained.|140 psf|1 hr
16 min|||7|1, 5|11/4| |F/C-4-RC-11|4″|4″ thick (4000 psi) concrete deck;
3″ × 11/2″ × 4 lbs R.S.J.; 2′6″ C.R.S.; flush
with top surface; 4″ × 6″ x 13 SWG mesh
reinforcement 1″ from bottom of slab; 6′6″
span restrained.|150 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-12|4″|4″ deep (2380 psi) concrete deck;
3″ × 11/2″ × 4 lbs R.S.J.; 2′6″ C.R.S.; flush
with top surface; 4″ × 6″ x 13 SWG mesh
reinforcement 1″ from bottom surface;
6′6″ span restrained.|150 psf|1 hr
3 min|||7|1, 2|1| |F/C-4-RC-13|41/2″|41/2″ thick (5200 psi) deck;1/4″ reinforce-
ment bars at 71/4″ pitch with7/8″ cover;3/8″
main reinforcement bars at 33/4″ pitch
perpendicular with1/2″ cover; 13′1″ span
restrained.|140 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-14|41/2″|41/2″ deep (2525 psi) concrete deck;1/4″
reinforcement bars at 71/2″ pitch with7/8″
cover;3/8″ main reinforcement bars at
33/8″ pitch perpendicular with1/2″ cover;
13′1″ span restrained.|150 psf|42 min|||7|1, 5|2/3| |F/C-4-RC-15|41/2″|41/2″ deep (4830 psi) concrete deck;
11/2″ × No.CMC § 12.6.8.2 High relevance — show source text
Exception: Direct vent appliances designed for installation in a solid-fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.8.2] 802.6 Gas Vents. The installation of gas vents shall meet the following requirements:
(1) Gas vents shall be installed in accordance with the manufacturer’s installation instructions.
(2) A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is
connected.
(3) Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel–burning appliances or incinerators.”
(4) Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent.
[NFPA 54:12.7.2] 802.6.1 Gas Vent Termination. The termination of gas vents shall comply with the following requirements:
(1) A gas vent shall terminate in accordance with one of the following:
(a) Gas vents that are 12 inches (300 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall
terminate above the roof in accordance with Figure 802.6.1 and Table 802.6.1.
(b) Gas vents that are over 12 inches (300 mm) in size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall
terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above a portion of a building within 10 feet (3048 mm) horizontally.
(c) Industrial appliances as provided in Section 802.2.5.
(d) Direct vent systems as provided in Section 802.2.6.
(e) Appliances with integral vents as provided in Section 802.2.7.
(f) Mechanical draft systems as provided in Section 802.3.3 through Section 802.3.3.4.
(g) Ventilating hoods and exhaust systems as provided in Section 802.3.4.
(2) A Type B or a Type L gas vent shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood or flue collar.
(3) A Type B-W gas vent shall terminate at least 12 feet (3658 mm) in vertical height above the bottom of the wall furnace.
(4) A gas vent extending through an exterior wall shall not terminate adjacent to the wall or below eaves or parapets, except as provided in Section 802.2.6 and Section 802.3.3 through Section 802.3.3.4.
(5) Decorative shrouds shall not be installed at the termination of gas vents except where such shrouds are listed for use with the specific gas venting system and are installed in accordance with the manufac turer’s installation instructions.
CMC § 2308.8.1.2 High relevance — show source text
2308.8.1.2 Atmospheric venting. Atmospheric venting of CNG shall comply with Sections 2308.8.1.2.1 through 2308.8.1.2.6.
2308.8.1.2.1 Plans and specifications. A drawing illustrating the location of the vessel support, piping, the method of grounding and bonding, and other requirements specified herein shall be provided to the fire code official for review and approval.
2308.8.1.2.2 Cylinder stability. A method of rigidly supporting the vessel during the venting of CNG shall be provided. The selected method shall provide not less than two points of support and shall prevent the horizontal and lateral movement of the vessel. The system shall be designed to prevent the movement of the vessel based on the highest gas-release velocity through valve orifices at the vessel’s rated pressure and volume. The structure or appurtenance shall be constructed of noncombustible materials.
2308.8.1.2.3 Separation. The structure or appurtenance used for stabilizing the cylinder shall be separated from the site equipment, features and exposures and shall be located in accordance with Table 2308.8.1.2.3.
23-12 2025 CALIFORNIA FIRE CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MOTOR FUEL-DISPENSING FACILITIES AND REPAIR GARAGES
TABLE 2308.8.1.2.3—SEPARATION DISTANCE FOR ATMOSPHERIC VENTING OF CNG Col2 EQUIPMENT OR FEATURE MINIMUM SEPARATION (feet) Buildings 25 Building openings 25 CNG compressor and storage vessels 25 CNG dispensers 25 Lot lines 15 Public ways 15 Vehicles 25 For SI: 1 foot = 304.8 mm. For SI: 1 foot = 304.8 mm. 2308.8.1.2.4 Grounding and bonding. The structure or appurtenance used for supporting the cylinder shall be grounded in accordance with the California Electrical Code. The cylinder valve shall be bonded prior to the commencement of venting operations.
2308.8.1.2.5 Vent tube. A vent tube that will divert the gas flow to the atmosphere shall be installed on the cylinder prior to commencement of the venting and purging operation. The vent tube shall be constructed of pipe or tubing materials approved for use with CNG in accordance with Chapter 53.
The vent tube shall be capable of dispersing the gas not less than 10 feet (3048 mm) above grade level. The vent tube shall not be provided with a rain cap or other feature that would limit or obstruct the gas flow.
At the connection fitting of the vent tube and the CNG cylinder, a listed bidirectional detonation flame arrester shall be provided.
2308.8.1.2.6 Signage. Approved “No Smoking” signs complying with Section 310 shall be posted within 10 feet (3048 mm) of the cylinder support structure or appurtenance. Approved “Cylinder Shall Be Bonded” signs shall be posted on the cylinder support structure or appurtenance.
SECTION 2309—HYDROGEN MOTOR FUEL-DISPENSING AND GENERATION FACILITIES
CMC § 1310.3.4 High relevance — show source text
1310.3.4 Prohibited Locations. Gas piping inside any building shall not be installed in or through a clothes chute, chimney or gas vent, dumbwaiter, elevator shaft, or air duct, other than combustion air ducts. [NFPA 54:7.2.5]
Exception: Ducts used to provide ventilation air in accordance with Section 701.0 or to above-ceiling spaces in accordance with Section 1310.3.3.1.
1310.3.5 Hangers, Supports, and Anchors. Piping shall be supported with metal pipe hooks, metal pipe straps, metal bands, metal brackets, metal hangers, or building structural components, suitable for the size of piping, of adequate strength and quality, and located at intervals so as to prevent or damp out excessive vibration. Piping shall be anchored to prevent undue strains on connected appliances and equipment and shall not be supported by other piping. Pipe hangers and supports shall conform to the requirements of MSS SP-58. [NFPA 54:7.2.6.1]
1310.3.5.1 Spacing. Spacing of supports in gas piping installations shall not be greater than shown in Table 1310.3.5.1. Spacing of supports of CSST shall be in accordance with the CSST manufac turer’s instructions. [NFPA 54:7.2.6.2]
TABLE 1310.3.5.1
SUPPORT OF PIPING
[NFPA 54: TABLE 7.2.6.2]
STEEL PIPE,
NOMINAL SIZE
OF PIPE(inches)SPACING OF
SUPPORTS
(feet)NOMINAL SIZE
OF TUBING
SMOOTH WALL
(inches O.D.)SPACING OF
SUPPORTS
(feet)1⁄2 6 1⁄2 4
3⁄4 or 18 5⁄8 or3⁄4 6
11⁄4 or larger
(horizontal)10 7⁄8 or 1
(horizontal)8
11⁄4 or larger
(vertical)Every floor
level1 or larger
(vertical)Every floor
levelFor SI units: 1 inch = 25 mm, 1 foot = 304.8 mm
1310.3.5.2 Expansion and Contraction. Supports, hangers, and anchors shall be installed so as not to interfere with the free expansion and contraction of the piping between anchors. All parts of the supporting system shall be designed and installed so they are not disengaged by movement of the supported piping. [NFPA 54:7.2.6.3]
1310.3.5.3 Piping on Roofs. Gas piping installed on the roof surfaces shall be supported in accordance with Table 1310.3.5.1. Gas piping shall be elevated not less than 3½ inches (89 mm) above the roof surface. [NFPA 54:7.2.6.4.1, 7.2.6.4.2]
CMC § 12.6.5.2 High relevance — show source text
chimney. Where two or more openings are provided into one chimney flue, they shall be at different levels. Where the gas appliance is automatically controlled, it shall be equipped with a safety shutoff device. [NFPA 54:12.6.5.2] 509.5.7.2 Gas and Solid Fuel-Burning Appli- ances. A listed combination gas- and solid-fuelburning appliance connected to a single chimney flue shall be equipped with a manual reset device to shut off gas to the main burner in the event of sustained backdraft or flue gas spillage. The chimney flue shall be sized to properly vent the appliance.
[NFPA 54:12.6.5.3] 509.5.7.3 Combination Gas- and Oil-Burning Appliances. A single chimney flue serving a listed combination gas- and oil-burning appliance shall be sized in accordance with the appliance manufacturer’s instructions. [NFPA 54:12.6.5.4] 509.5.8 Support of Chimneys. All portions of chimneys shall be supported for the design and weight of the materials employed. Listed factory-built chimneys shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.6] 509.5.9 Cleanouts. Where a chimney that formerly carried flue products from liquid or solid fuel-burning appliances is used with an appliance using fuel gas, an accessible cleanout shall be provided. The cleanout shall have a tight-fitting cover and be installed so its upper edge is at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening. [NFPA 54:12.6.7] 509.5.10 Space Surrounding Lining or Vent. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appli ance.
Exception: The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer’s instructions. [NFPA 54:12.6.8.1] 509.5.10.1 Combustion Air. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory-built chimney flue 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 54:12.6.8.2] 509.6 Gas Vents. The installation of gas vents shall meet the following requirements:
(1) Gas vents shall be installed in accordance with the manufacturer’s installation instructions.
(2) A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is
connected.
(3) Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry
94 2025 CALIFORNIA PLUMBING CODE
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Frequently asked questions
Who sets the actual hanger spacing for a listed gas vent?
The vent manufacturer (the product’s installation instructions or listing). The CMC’s § 802.6.4 requires you to follow those instructions.
Can I use the gas‑piping hanger spacing table for gas vents?
No. Gas‑piping support spacing appears in the piping sections (e.g., § 1310.3.5 and its table), but § 802.6.4 tells you vent support/spacing is per the vent manufacturer.
Are there any prohibitions on fasteners through vents?
Yes — the CMC states screws, rivets, and fasteners shall not penetrate the inner wall of double‑wall gas vents except at the appliance transition; follow the manufacturer for permitted fastener locations.
What if the manufacturer instructions are missing or unclear?
You must obtain the listed manufacturer instructions before completing the installation. If they are unclear, contact the vent manufacturer for clarification or follow a listed alternative product’s instructions. The CMC itself provides no numeric spacing in § 802.6.4.
Do chimneys follow the same rule?
Factory‑built chimneys and vents are both supported per the manufacturer’s instructions; see § 802.5.9 for chimneys.
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