CMC · California Mechanical Code
What are the rules for single‑wall metal pipe connectors and clearances?
For nonresidential uses where allowed, single‑wall metal pipe must be kept the minimum distances from combustible materials shown in Table 802.7.3.3 (see § 802.7.3.3). Listed appliance instructions and specific vent‑connector protection rules can require different or reduced clearances; single‑wall pipe may not originate in attics or pass through concealed spaces.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Single‑wall metal pipe connectors must maintain minimum clearances to combustible materials as listed in § 802.7.3.3; those minimum distances come from Table 802.7.3.3. Single‑wall metal pipe is limited to direct runs from the appliance to the outdoors (not through attics or concealed spaces) and is subject to termination, thimble and wall‑penetration requirements elsewhere in § 802.7. These clearance requirements are mandatory unless a specific appliance or connector listing or a permitted protection system reduces the clearance per the vent‑connector rules.
The most important rule: keep the minimum clearances in § 802.7.3.3 (see Table 802.7.3.3) between a single‑wall metal pipe (and its connector) and any combustible material unless a permitted, code‑specified protection reduces it.
Requirements in detail
Where these requirements live
- The clearance rule is stated in § 802.7.3.3 (see Table 802.7.3.3) of the CMC.
- The table of numeric minimum clearances is reproduced as Table 802.7.3.3 in the code.
Key plain‑English points
- Single‑wall metal pipe may only be used where allowed by Section § 802.7 and must run directly from the appliance to the roof or exterior wall — it cannot originate or pass through unoccupied attics, concealed spaces, inside walls or floors. § 802.7.3.1 and § 802.7.3.2.
- Minimum clearances to combustible materials vary by appliance category / heat class; the table (below) gives the controlling distances for single‑wall metal pipe. § 802.7.3.3.
- Where the appliance or connector is listed with different clearances, the appliance/listing instructions control (i.e., listed clearances take precedence). § 802.7.3.3.
Decision‑relevant dimensions (quick reference)
| Appliance / situation | Minimum clearance to single‑wall metal pipe (inches) | Code Reference |
|---|---|---|
| Listed appliances with draft hoods and appliances listed for use with Type B gas vents | 6 in | § 802.7.3.3 |
| Residential boilers & furnaces with listed gas conversion burner and draft hood | 9 in | § 802.7.3.3 |
| Residential appliances listed for use with Type L vents | 9 in | § 802.7.3.3 |
| Unlisted residential appliances with draft hood | 9 in | § 802.7.3.3 |
| Residential and low‑heat appliances (other than above) | 18 in | § 802.7.3.3 |
| Medium‑heat appliances | 36 in | § 802.7.3.3 |
Notes:
- These clearances are the minimum distances to combustible material when no special protection is used; where a listed appliance or connector gives different clearances, that listing controls. § 802.7.3.3.
Protection and reduced clearances
- The code allows reduced clearances only as specified for vent connectors (i.e., by the vent‑connector protection tables and rules). The general allowance for reduction is stated in § 802.7.3.3: "Reduced clearances ... shall be as specified for vent connectors." For the specifics of how much clearance can be reduced and what protection is required, consult the vent‑connector protection tables and text for vent connectors (see § 802.10.4 and the connector protection tables).
Exceptions & special cases
- Single‑wall metal pipe shall not be used as a vent in dwellings and residential occupancies unless specifically permitted by Section § 802.4; verify allowed appliance types before applying the clearances. § 802.7.3 (installation with appliances permitted by § 802.4).
- Where single‑wall pipe passes through a roof of combustible construction, a noncombustible, non‑ventilating roof thimble is required; the thimble sizing and extension requirements are in § 802.7.3.4 and § 802.7.3.5.
- Where a single‑wall pipe passes through a combustible exterior wall, a ventilated metal thimble (sized per § 802.7.3.5) or removal of combustible material to provide the required clearance is required. § 802.7.3.5.
- If the appliance or connector is listed with its own clearance requirements, those listed instructions control over the generic table distances. § 802.7.3.3.
Common mistakes
- Assuming single‑wall pipe clearances are the same for all appliances — clearance depends on appliance category / heat class; check the table in § 802.7.3.3.
- Trying to run single‑wall pipe through attics, concealed spaces or interior walls — the code forbids those uses for single‑wall pipe. § 802.7.3.1 / § 802.7.3.2.
- Reducing clearances without applying the specific vent‑connector protection methods listed in the code — reductions are only allowed when the specific protection for vent connectors is used and permitted. § 802.7.3.3 and vent‑connector sections.
- Forgetting that listed appliances/connector manufacturer instructions can override the generic table — the listing/instructions may require larger or different clearances. § 802.7.3.3.
Worked example — concrete scenario
Scenario: A commercial laundry room has a medium‑heat gas dryer appliance (not a residential occupancy). A 6‑inch diameter single‑wall metal pipe runs vertically from the dryer up through the roof. There is a combustible framed partition located nearby.
Step 1 — Determine appliance category: "medium‑heat appliance." Check the single‑wall pipe clearance for medium‑heat appliances: 36 inches to combustible material per Table 802.7.3.3 (controlled by § 802.7.3.3). So the pipe must be at least 36 in from the combustible partition.
Step 2 — Consider reductions: If the installer wants to place the pipe closer, they must apply a code‑permitted protection system for vent connectors (for example, a listed wall protector or specified insulation/air‑gap system). The allowable reduction and the required protector construction are given in the vent‑connector protection rules/tables; consult the vent‑connector provisions before reducing clearance. § 802.7.3.3 and vent‑connector sections.
Step 3 — Check other requirements: ensure the pipe does not originate in an attic or pass through concealed spaces, and that roof thimble and termination requirements are met (see § 802.7.3.2, § 802.7.3.4 and § 802.7.2).
Result: Without protection, keep at least 36 in clearance. To reduce, follow the vent connector protection tables and manufacturer/listing instructions.
Related provisions
- § 802.7.1 — Cold climate restriction for uninsulated single‑wall pipe.
- § 802.7.2 — Termination height requirements for single‑wall metal pipe.
- § 802.7.3.1 — Limitations: single‑wall pipe runs must be direct to roof/exterior.
- § 802.7.3.2 — Prohibition on originating or passing through attics, concealed spaces, inside walls or floors.
- § 802.7.3.4 — Roof thimble requirements where single‑wall pipe passes through combustible roofs.
- § 802.7.3.5 — Combustible exterior wall thimble sizing and alternatives.
- § 802.7.4 — Sizing rules for single‑wall metal pipe.
- § 802.7.5 — Support requirements for single‑wall metal pipe.
- § 802.10.4 — Clearance rules for vent connectors and reference to protection/reduction provisions.
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 802.7.3.2 High relevance — show source text
802.7.3.2 Attic or Concealed Space. Singlewall metal pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic, inside wall, concealed space, or floor. [NFPA 54:12.8.4.3]
802.7.3.3 Clearances. Minimum clearances from
single-wall metal pipe to combustible material shall be in accordance with Table 802.7.3.3. Reduced
clearances from single-wall metal pipe to combustible material shall be as specified for vent connectors. [NFPA 54:12.8.4.4]
802.7.3.4 Roof Thimble. Where a single-wall metal pipe passes through a roof constructed of combustible material, a noncombustible, nonventilating thimble shall be used at the point of passage. The thimble shall extend at least 18 inches (457 mm) above and 6 inches (152 mm) below the roof with the annular space open at the bottom and closed only at the top. The thimble shall be sized in accordance with Section 802.7.3.5. [NFPA 54:12.8.4.5] 802.7.3.5 Combustible Exterior Wall. Singlewall metal pipe shall not pass through a combustible exterior wall unless guarded at the point of passage by a ventilated metal thimble not smaller than the following:
(1) For listed appliances with draft hoods and appliances listed for use with Type B gas vents, the thimble shall be a minimum of 4 inches (102 mm) larger in diameter than the metal pipe. Where there is a run of not less than 6 feet
(1829 mm) of metal pipe in the opening between the draft hood outlet and the thimble, the thimble shall be a minimum of 2 inches (51 mm) larger in diameter than the metal pipe.
(2) For unlisted appliances having draft hoods, the thimble shall be a minimum of 6 inches (152 mm) larger in diameter than the metal pipe.
(3) For residential and low-heat appliances, the thimble shall be a minimum of 12 inches (305 mm) larger in diameter than the metal pipe.
Exception: In lieu of thimble protection, all combustible material in the wall shall be removed a suffi cient distance from the metal pipe to provide the
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2025 CALIFORNIA MECHANICAL CODE 159
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CHIMNEYS AND VENTS
specified clearance from such metal pipe to combustible material. Any material used to close up such opening shall be noncombustible. [NFPA 54:12.8.4.6] 802.7.4 Size of Single-Wall Metal Pipe. Single-wall metal piping shall comply with the following require ments:
(1) A venting system of a single-wall metal pipe shall be sized in accordance with one of the following methods and the appliance manufacturer’s instructions:
(a) For a draft hood-equipped appliance, in accordance with Section 803.0.
CMC § 802.7.1 High relevance — show source text
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]
802.7.3 Installation with Appliances Permitted by Section 802.4. Single-wall metal pipe shall not be used as a vent in dwellings and residential occupancies.
[NFPA 54:12.8.4.1]
802.7.3.1 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]
802.7.3.2 Attic or Concealed Space. Singlewall metal pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic, inside wall, concealed space, or floor. [NFPA 54:12.8.4.3]
802.7.3.3 Clearances. Minimum clearances from
single-wall metal pipe to combustible material shall be in accordance with Table 802.7.3.3. Reduced
clearances from single-wall metal pipe to combustible material shall be as specified for vent connectors. [NFPA 54:12.8.4.4]
802.7.3.4 Roof Thimble. Where a single-wall metal pipe passes through a roof constructed of combustible material, a noncombustible, nonventilating thimble shall be used at the point of passage. The thimble shall extend at least 18 inches (457 mm) above and 6 inches (152 mm) below the roof with the annular space open at the bottom and closed only at the top. The thimble shall be sized in accordance with Section 802.7.3.5. [NFPA 54:12.8.4.5] 802.7.3.5 Combustible Exterior Wall. Singlewall metal pipe shall not pass through a combustible exterior wall unless guarded at the point of passage by a ventilated metal thimble not smaller than the following:
(1) For listed appliances with draft hoods and appliances listed for use with Type B gas vents, the thimble shall be a minimum of 4 inches (102 mm) larger in diameter than the metal pipe. Where there is a run of not less than 6 feet
California Mechanical Code High relevance — show source text
**|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
**CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.CMC § 509.7.3.4 High relevance — show source text
DISTANCE SPECIFIED AS THE**
REQUIRED CLEARANCE WITH NO
PROTECTION [SEE FIGURE
509.7.3.4(1) THROUGH FIGURE
509.7.3.4(3)]|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.| |TYPE OF PROTECTION APPLIED TO
AND COVERING ALL SURFACES OF
COMBUSTIBLE MATERIAL WITHIN
THE DISTANCE SPECIFIED AS THE
REQUIRED CLEARANCE WITH NO
PROTECTION [SEE FIGURE
509.7.3.4(1) THROUGH FIGURE
**509.7.3.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
California Mechanical Code High relevance — show source text
(INCHES)**|18 (INCHES)|12 (INCHES)|12 (INCHES)|9 (INCHES)|9 (INCHES)|6 (INCHES)|6 (INCHES)| |TYPE OF PROTECTION
APPLIED TO AND COVERING
ALL SURFACES OF COM-
BUSTIBLE MATERIAL
WITHIN THE DISTANCE
SPECIFIED AS THE
REQUIRED CLEARANCE
WITH NO PROTECTION|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (INCHES)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (INCHES)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (INCHES)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (INCHES)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (INCHES)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (INCHES)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (INCHES)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (INCHES)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (INCHES)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (INCHES)| |TYPE OF PROTECTION
APPLIED TO AND COVERING
ALL SURFACES OF COM-
BUSTIBLE MATERIAL
WITHIN THE DISTANCE
SPECIFIED AS THE
REQUIRED CLEARANCE
WITH NO PROTECTION|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR
**CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.CMC § 7.3.4 High relevance — show source text
7.3.4(3)]**|36 (inches)|36 (inches)|18 (inches)|18 (inches)|12 (inches)|12 (inches)|9 (inches)|9 (inches)|6 (inches)|6 (inches)| |TYPE OF PROTECTION APPLIED TO
AND COVERING ALL SURFACES OF
COMBUSTIBLE MATERIAL WITHIN
THE DISTANCE SPECIFIED AS THE
REQUIRED CLEARANCE WITH NO
PROTECTION [SEE FIGURE
509.7.3.4(1) THROUGH FIGURE
509.7.3.4(3)]|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)|ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)| |TYPE OF PROTECTION APPLIED TO
AND COVERING ALL SURFACES OF
COMBUSTIBLE MATERIAL WITHIN
THE DISTANCE SPECIFIED AS THE
REQUIRED CLEARANCE WITH NO
PROTECTION [SEE FIGURE
509.7.3.4(1) THROUGH FIGURE
509.7.3.4(3)]|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2
FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.|**USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR.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 § 12.8.5 High relevance — show source text
(c) Engineering methods.
(2) Where a single-wall metal pipe is used and has a shape other than round, it shall have an equivalent effective area equal to the effective area of the round pipe for which it is substituted and the minimum internal dimension of the pipe shall be 2 inches (51 mm).
(3) The vent cap or a roof assembly shall have a venting capacity not less than that of the pipe to which it is attached. [NFPA 54:12.8.5]
802.7.5 Support of Single-Wall Metal Pipe. All portions of single-wall metal pipe shall be supported for the design and weight of the material employed. [NFPA 54:12.8.6]
802.7.6 Marking. Single-wall metal pipe shall comply with the marking provisions of Section 802.6.5. [NFPA 54:12.8.7]
802.8 Through-the-Wall Vent Termination. Throughthe-wall vent termination shall be in accordance with Section
802.8.1 through Section 802.8.3.
802.8.1 Clearance for Through-the-Wall Vent Ter- mination. The clearance for through-the-wall direct vent and non-direct vent terminals shall be in accordance with
Table 802.8.1 and Figure 802.8.1.
Exception: The clearances in Table 802.8.1 shall not apply to the combustion air intake of a direct vent appliance. [NFPA 54:12.9.1]
802.8.2 Annular Spaces. Where vents, including those for direct vent appliances or combustion air intake pipes, penetrate outside walls of buildings, the annular spaces around such penetrations shall be permanently sealed using approved materials to prevent entry of combustion products into the building. [NFPA 54:12.9.2]
802.8.3 Vent Terminals. Vent systems for Category IV appliances that terminate through an outside wall of a building and discharge flue gases perpendicular to the adjacent wall shall be located not less than 10 feet (3048 mm) horizontally from an operable opening in an adjacent building.
Exception: This shall not apply to vent terminals that are 2 feet (610 mm) or more above or 25 feet (7620 mm) or more below operable openings. [NFPA 54:12.9.3]
802.9 Condensation Drain. Provision shall be made to
collect and dispose of condensate from venting systems serving Category II and Category IV appliances and noncategorized condensing appliances. [NFPA 54:12.10.1]
802.9.1 Installation. Drains for condensate shall be
installed in accordance with the appliance and vent manufacturers’ installation instructions. [NFPA 54:12.10.2]
802.10 Vent Connectors for Category I Appliances. A vent connector shall be used to connect an appliance to a gas vent, chimney, or single-wall metal pipe, except where the gas vent, chimney, or single-wall metal pipe is directly connected to the appliance. [NFPA 54:12.11.1]
802.10.1 Materials. A vent connector shall be made of
noncombustible, corrosion-resistant material capable of
«
«
|TABLE 802.7.3.3 CLEARANCE FOR CONNECTORS* [NFPA 54: TABLE 12.8.4.
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 § 509.7.2 High relevance — show source text
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]
509.7.3.2 Attic or Concealed Space. Singlewall metal pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic, inside wall, concealed space, or floor. [NFPA 54:12.8.4.3]
509.7.3.3 Incinerator. Single-wall metal pipe used for venting an incinerator shall be exposed and readily examinable for its full length and shall have required clearances maintained.
509.7.3.4 Clearances. Minimum clearances from single-wall metal pipe to combustible material shall be in accordance with Table 509.7.3.4(1). Reduced clearances from single-wall metal pipe to combustible material shall be as specified for vent connectors in Table 509.7.3.4(2). [NFPA 54:12.8.4.4]
509.7.3.5 Combustible Exterior Wall. Singlewall metal pipe shall not pass through a combustible exterior wall unless guarded at the point of passage by a ventilated metal thimble not smaller than the following:
(1) For listed appliances with draft hoods and appliances listed for use with Type B gas vents, the thimble shall be a minimum of 4 inches (100 mm) larger in diameter than the metal pipe. Where there is a run of not less than 6 feet (1829 mm) of metal pipe in the opening between the draft hood outlet and the thimble, the thimble shall be a minimum of 2 inches (50 mm) larger in diameter than the metal pipe.
(2) For unlisted appliances having draft hoods, the thimble shall be a minimum of 6 inches (150 mm) larger in diameter than the metal pipe.
|TABLE 509.7.3.4(1) CLEARANCES FOR CONNECTORS {NFPA 54: TABLE 12.8.4.
CMC § 509.7.3.3 High relevance — show source text
509.7.3.3 Incinerator. Single-wall metal pipe used for venting an incinerator shall be exposed and readily examinable for its full length and shall have required clearances maintained.
509.7.3.4 Clearances. Minimum clearances from single-wall metal pipe to combustible material shall be in accordance with Table 509.7.3.4(1). Reduced clearances from single-wall metal pipe to combustible material shall be as specified for vent connectors in Table 509.7.3.4(2). [NFPA 54:12.8.4.4]
509.7.3.5 Combustible Exterior Wall. Singlewall metal pipe shall not pass through a combustible exterior wall unless guarded at the point of passage by a ventilated metal thimble not smaller than the following:
(1) For listed appliances with draft hoods and appliances listed for use with Type B gas vents, the thimble shall be a minimum of 4 inches (100 mm) larger in diameter than the metal pipe. Where there is a run of not less than 6 feet (1829 mm) of metal pipe in the opening between the draft hood outlet and the thimble, the thimble shall be a minimum of 2 inches (50 mm) larger in diameter than the metal pipe.
(2) For unlisted appliances having draft hoods, the thimble shall be a minimum of 6 inches (150 mm) larger in diameter than the metal pipe.
TABLE 509.7.3.4(1) CLEARANCES FOR CONNECTORS {NFPA 54: TABLE 12.8.4.4}* Col2 Col3 Col4 Col5 MINIMUM DISTANCE FROM COMBUSTIBLE MATERIAL (inches) MINIMUM DISTANCE FROM COMBUSTIBLE MATERIAL (inches) MINIMUM DISTANCE FROM COMBUSTIBLE MATERIAL (inches) MINIMUM DISTANCE FROM COMBUSTIBLE MATERIAL (inches) MINIMUM DISTANCE FROM COMBUSTIBLE MATERIAL (inches) APPLIANCE LISTED TYPE B GAS
VENT MATERIALLISTED TYPE L VENT
MATERIALSINGLE-WALL METAL
PIPEFACTORY-BUILT
CHIMNEY SECTIONSListed appliances with draft hoods and appli-
ances listed for use with Type B gas ventsAs listed As listed 6 As listed Residential boilers and furnaces with listed gas
conversion burner and with draft hood6 6 9 As listed Residential appliances listed for use with
Type L ventsNot permitted As listed 9 As listed Unlisted residential appliances with draft hood Not permitted 6 9 As listed Residential and low-heat appliances other than
those aboveNot permitted 9 18 As listed Medium-heat appliances Not permitted Not permitted 36 As listed For SI units: 1 inch = 25.4 mm
- These clearances shall apply unless the installation instructions of a listed appliance or connector specify different clearances, in which case the listed clearances shall apply.
2025 CALIFORNIA PLUMBING CODE 97
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
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Frequently asked questions
Can single‑wall metal pipe be used in a house?
No—single‑wall metal pipe is generally not permitted as a vent in dwellings and residential occupancies except where Section § 802.4 specifically allows it; always confirm appliance type and applicable allowances. § 802.7.3 (installation with appliances permitted by § 802.4).
What if my appliance manufacturer gives different clearances?
Follow the listed appliance or connector instructions if they specify different clearances; listed instructions take precedence over the generic table in § 802.7.3.3.
Can I cover nearby combustible walls with metal to reduce clearance?
Potentially—clearance reductions are allowed only when the combustible surfaces are protected by a code‑approved protection system specified for vent connectors. Consult the vent‑connector protection tables and text for allowed methods and dimensions. § 802.7.3.3 and vent connector sections.
Are the clearance numbers absolute or minimums?
They are minimums; larger clearances are acceptable, and listed appliance/connector instructions may require larger clearances. § 802.7.3.3.
Where are the numeric clearances listed?
See Table 802.7.3.3 (the numeric minimum clearances to combustible material) referenced and required by § 802.7.3.3.
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