CMC · California Mechanical Code

What is a 'Vent', 'Vent Connector' and vent types (Type B, B‑W, L)?

A “vent” is the listed factory‑made pipe assembly that carries combustion gases outdoors; a “vent connector” is the short pipe from the appliance to that vent. Use the vent type the appliance is listed for (Type B for most gas appliances, Type B‑W for vented wall furnaces, Type L for certain oil appliances), size connectors per the CMC vent tables, and follow termination heights and material rules in the Chimneys & Vents chapter. If you need a ruling based on **§ 217.0**, that section was not present in the files you gave me — upload it or confirm the edition and I’ll cite it exactly.

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

A Vent is a factory‑made conduit assembly for conveying combustion products and air and must be listed and labeled for the appliance it serves (§ 224.0) — . A Vent Connector is the portion of the gas‑venting system that connects the appliance (at the draft hood or flue collar) to a vent and is installed entirely within the room or space of the appliance (§ 224.0) — . The CMC recognizes specific factory‑made vent types — Type B, Type B‑W, and Type L — each listed for particular appliances and installations; use the manufacturer instructions and the sizing/termination rules in the Chimneys and Vents chapter (see § 802.x and § 803.x) to select and size them — .

The simplest rule: use a listed vent system and the vent type the appliance is listed for; use a listed vent connector sized per the venting tables and follow the vent termination and material rules in § 802 and the sizing tables in § 803 — .

(Note: the user requested controlling section § 217.0. The files provided do not contain a § 217.0; the definitions and requirements cited below are taken from the CMC sections and tables available in the provided document excerpts — I state that plainly where relevant.)

Requirements in detail

Core definitions (first mention bolded)

  • Vent — § 224.0: “A pipe or other conduit composed of factory‑made components…listed and labeled for use with a specific type or class of appliance.”
  • Vent, Type B Gas — § 224.0: factory‑made gas vent listed for appliances that burn only gas.
  • Vent, Type B‑W Gas — § 224.0: factory‑made gas vent listed for gas‑fired vented wall furnaces (wall‑furnace specific).
  • Vent, Type L Gas — § 224.0: listed vent piping and fittings used with oil‑burning appliances listed for Type L or with listed gas appliances.
  • Vent Connector, Gas — § 224.0: the connector from appliance draft hood/flue collar to the vent; entirely within the appliance space.

Material & installation requirements (decision‑relevant)

Use the vent type and materials required for the appliance and location (examples below are decision drivers you must check):

Decision dimension Typical code value / rule Code reference
Appliance must use a listed vent and type it was listed for Vent must be listed and labeled for the specific appliance § 224.0 —
Vent connector in unconditioned space (attic/crawl) That portion of the connector must be Type B, Type L, or listed vent material with equivalent insulation qualities; exception for single‑wall in exterior walls when local 99% winter design temp ≥ 5°F (-15°C) § 802.10.1.1 —
Residential vent connector acceptable materials (non‑attic) Type B or Type L, or specific thicknesses of galvanized, aluminum, or stainless per § 802.10.1.2 § 802.10.1.2 —
Gas‑vent termination vertical clearance Type B or Type L: terminate at least 5 ft (1524 mm) above highest connected appliance draft hood/flue collar; Type B‑W: terminate at least 12 ft (3658 mm) above bottom of wall furnace § 802.6.1 (2)–(3) —
Do not penetrate inner wall of double‑wall vent with fasteners Screws, rivets, other fasteners shall not penetrate inner wall except at transition to draft hood/flue collar or single‑wall connector § 802.6 (4) —
Sizing vent/connectors Use the vent connector and common vent capacity tables in § 803.1.2 / § 803.2 (multiple tables for Type B, single‑wall connectors, masonry chimneys, etc.) § 803.1.2 / § 803.2 tables & Appendix examples —
Clearances to combustibles See Table in Chimneys & Vents (clearances differ by vent material and appliance) — some single‑wall connectors require 6–36 in clearances depending on appliance See clearance table in Chimneys & Vents —

(Consult the specific sizing table for exact diameters and capacities — the CMC provides many Table variants for different vent/connector combinations and appliance categories, see § 803 tables — .)

Selection guide (short)

  • If the appliance is listed for Type B vents (typical gas boilers/furnaces), use Type B venting and the appropriate connector sizing table (Type B double‑wall or single‑wall connector to Type B) — see § 803.1.2 tables — .
  • If the appliance is a vented wall furnace, use Type B‑W vent components (Type B‑W capacity and termination rules apply) — § 224.0 and § 802.6.1(3) — .
  • If the appliance is listed for Type L (some oil appliances or specific gas appliances), use Type L venting and the materials/clearances listed for Type L — § 224.0 and Chimneys & Vents tables — .

Exceptions & special cases

  • The CMC excerpts provided do not show § 217.0. If your project specifically relies on § 217.0, the provided document set does not contain it; consult the full CMC edition/authority having jurisdiction for § 217.0 text. (I will not invent or assume its content.) — (no file available for § 217.0)
  • Unconditioned spaces: a vent connector run in an attic or crawl space must be Type B, Type L, or a listed vent material with equivalent insulation qualities. There is an explicit exception allowing single‑wall pipe in exterior walls in unconditioned spaces where the local 99% winter design temperature is ≥ 5°F (-15°C) — § 802.10.1.1 — .
  • Exterior masonry chimneys: special rules require Type B connectors when venting into exterior masonry chimneys and specific tables for sizing when double‑wall connectors are used — see the masonry‑chimney tables in § 803 — .

Common mistakes

  • Selecting the wrong vent type for the appliance (e.g., using Type B for a wall furnace that requires Type B‑W). Definitions make the appliance‑vent pairing binding — § 224.0 — .
  • Ignoring termination heights: failing to meet the 5 ft (Type B/L) or 12 ft (Type B‑W wall furnace) vertical clearances — § 802.6.1(2)–(3) — .
  • Penetrating the inner wall of a double‑wall vent with screws/fasteners — prohibited except at the transition point — § 802.6 (4) — .
  • Improperly sizing vent connectors by eye instead of using the appropriate § 803 tables (Type B tables vs. single‑wall connector tables vs. masonry‑chimney tables). This causes draft problems and code noncompliance — see § 803 tables and Appendix examples — .
  • Running single‑wall connectors through attics/crawl spaces without meeting the Type B/L or listed insulation requirement in § 802.10.1.1 — .

Worked example — concrete scenario

Scenario: You have a draft‑hood equipped gas appliance with 120,000 Btu/h input and a Type B vent that rises 10 ft (3048 mm) vertically. The installer will use a 5 ft (1524 mm) lateral single‑wall metal vent connector with two 90° elbows. What vent diameter?

  • The CMC example in Appendix F follows this exact scenario and shows that you must use Table 803.1.2(2) (single‑wall vent connector attached to a Type B double‑wall vent) to find connector capacity. Using the table for H = 10 ft, lateral = 5 ft, with two elbows, a 5‑inch (127 mm) diameter vent has a capacity of 122,000 Btu/h, which is sufficient for the 120,000 Btu/h appliance — therefore a 5‑inch vent is acceptable in that configuration (the Appendix example demonstrates the steps) — see Appendix F Example and Table 803.1.2(2) — .

(If you add a third elbow or increase lateral length, the example shows capacity drops and you may be forced to increase to 6‑inch — Appendix F example and calculations explain the adjustment factors — .)

Related provisions

  • § 224.0 — Definitions for Vent, Vent Connector, Type B, Type B‑W, Type L —
  • § 802.6 — Gas vents: installation rules, fastener prohibition, labels when installed in masonry chimneys —
  • § 802.6.1 — Gas vent termination clearances (including 5 ft and 12 ft rules) —
  • § 802.10.1.1 — Vent connector requirements in unconditioned spaces (Type B/L or listed equivalent; exception for 5°F threshold) —
  • § 802.10.1.2 — Residential vent connector material thicknesses and permitted materials —
  • § 803.1.2 / § 803.2 — Vent and vent‑connector sizing tables (Type B, single‑wall, masonry chimneys, common venting) and worked examples in Appendix F —

I did not find § 217.0 in the provided CMC excerpts; the definitions and mandatory vent/connector rules above are taken from the sections and tables present in the supplied files (definitions at § 224.0, vent/connector rules in § 802.x and sizing in § 803.x). If you need a direct quote or the text of § 217.0, please upload the CMC pages that contain § 217.0 or tell me the specific edition/version so I can look it up in your files.

Code references

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

  • CMC § 3.3.53 High relevance — show source text

    Valves, Companion or Block. Pairs of mating stop valves valving off sections of refrigeration systems and arranged so that these sections may be joined before opening these valves or separated after closing them.

    Vent. A pipe or other conduit composed of factory-made components, containing a passageway for conveying combustion products and air to the atmosphere, listed and labeled for use with a specific type or class of appliance. Vent, Type B Gas. A factory-made gas vent listed by a nationally recognized testing agency for venting listed or approved appliances equipped to burn only gas. Vent, Type B-W Gas. A factory-made gas vent listed by a nationally recognized testing agency for venting listed or approved gas-fired vented wall furnaces. Vent, Type L Gas. A venting system consisting of listed vent piping and fittings for use with oil-burning appliances listed for use with Type L or with listed gas appliances. Vent, Gas. A passageway composed of listed factory-built components assembled in accordance with the manufacturer’s installation instructions for conveying vent gases from appliances or their vent connectors to the outdoors. [NFPA 54:3.3.53] Vent Connector, Gas. That portion of a gas-venting system that connects a listed gas appliance beginning at the draft hood or flue collar to a gas vent and is installed entirely within the space or area in which the appliance is located. Vent Offset. An arrangement of two or more fittings and pipe installed for the purpose of locating a vertical section of vent pipe in a different but parallel plane with respect to an adjacent section of vertical vent pipe. [NFPA 54:3.3.101]

    2025 CALIFORNIA MECHANICAL CODE 47

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    DEFINITIONS

    Water Well. An excavation that is drilled, cored, bored, washed, driven, dug, jetted, or otherwise constructed for the purposes of extracting groundwater, using the geothermal properties of the earth or injecting water into an aquifer or subsurface reservoir.

    226.0 – X –

    No definitions.

    227.0 – Y –

    No definitions.

    228.0 – Z –

    Zeotropic. Blends comprising multiple components of different volatilities that, when used in refrigeration cycles, change volumetric composition and saturation temperatures as they evaporate (boil) or condense at constant pressure.

    [ASHRAE 34:3]

    Zone. [OSHPD 1, 2, 3, 4 & 5] A space or group of spaces within a building for which the heating, or cooling require- ments are sufficiently similar that desired conditions can be maintained throughout by a single controlling device.

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    CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE

    CHAPTER 3 – GENERAL REGULATIONS

    (Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

  • CMC § 225.0 High relevance — show source text

    Volume, Internal Gross. The volume as determined from internal dimensions of the container, with no allowance for the volume of the internal parts.

    225.0 – W –

    Wall Heater. See Vented Wall Furnace.

    Warm Air Furnace. An environmental heating appliance designed or arranged to discharge heated air through any duct or ducts. This definition shall not include a unit heater.

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    Unusually Tight Construction. Construction where:

    (1) Walls and ceilings exposed to the outdoors have a continuous water vapor retarder with a rating of 1 perm or less with openings gasketed or sealed.

    (2) Weatherstripping is on openable windows and doors.

    (3) Caulking or sealants are applied to areas such as joints around window and door frames, between sole plates and floors, between wall-ceiling joints, between wall panels, and at penetrations for plumbing, electrical, and gas lines and at other openings. Use (Material). The placing in action or making available for service by opening or connecting a container utilized for confinement of material, whether a solid, liquid, or gas.

    224.0 – V –

    Vacuum. A pressure less than that exerted by the atmosphere. Valve, Pressure-Relief. A pressure-actuated valve held closed by a spring or other means and designed to automatically relieve pressure in excess of its setting. Valve, Stop. A device in a piping system to shut off the flow of the fluid.

    Valve, Three-Way-Type Stop. A manually operated valve with one inlet that alternately can stop flow to either of two outlets.

    Valves, Companion or Block. Pairs of mating stop valves valving off sections of refrigeration systems and arranged so that these sections may be joined before opening these valves or separated after closing them.

    Vent. A pipe or other conduit composed of factory-made components, containing a passageway for conveying combustion products and air to the atmosphere, listed and labeled for use with a specific type or class of appliance. Vent, Type B Gas. A factory-made gas vent listed by a nationally recognized testing agency for venting listed or approved appliances equipped to burn only gas. Vent, Type B-W Gas. A factory-made gas vent listed by a nationally recognized testing agency for venting listed or approved gas-fired vented wall furnaces. Vent, Type L Gas. A venting system consisting of listed vent piping and fittings for use with oil-burning appliances listed for use with Type L or with listed gas appliances. Vent, Gas. A passageway composed of listed factory-built components assembled in accordance with the manufacturer’s installation instructions for conveying vent gases from appliances or their vent connectors to the outdoors. [NFPA 54:3.3.53] Vent Connector, Gas. That portion of a gas-venting system that connects a listed gas appliance beginning at the draft hood or flue collar to a gas vent and is installed entirely within the space or area in which the appliance is located. Vent Offset. An arrangement of two or more fittings and pipe installed for the purpose of locating a vertical section of vent pipe in a different but parallel plane with respect to an adjacent section of vertical vent pipe. [NFPA 54:3.3.101]

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  • CMC § 101.2 High relevance — show source text

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

    FIGURE F 101.2(7) VENT SYSTEM SERVING TWO OR MORE APPLIANCES WITH TYPE B DOUBLE-WALL VENT AND SINGLE-WALL METAL VENT CONNECTORS

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

    attached to a tile-lined masonry chimney.

    Notes:

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

    FIGURE F 101.2(8) MASONRY CHIMNEY SERVING TWO OR MORE APPLIANCES WITH TYPE B DOUBLE-WALL VENT CONNECTORS

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

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    hood-equipped appliance. [See Table 803.1.2(5)]

    FIGURE F 101.2(5) ASBESTOS CEMENT TYPE B OR SINGLE-WALL METAL VENT SYSTEM SERVING A SINGLE DRAFT HOOD-EQUIPPED APPLIANCE

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

    attached to a Type B double-wall common vent.

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

    FIGURE F 101.2(6) VENT SYSTEM SERVING TWO OR MORE APPLIANCES WITH TYPE B DOUBLE-WALL VENT AND TYPE B DOUBLE-WALL VENT CONNECTORS

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

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    APPENDIX F

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    attached to a tile-lined masonry chimney.

    Notes:

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

    FIGURE F 101.2(9) MASONRY CHIMNEY SERVING TWO OR MORE APPLIANCES WITH SINGLE-WALL METAL VENT CONNECTORS

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

    draft hood-equipped appliances. [See Table 803.2(5)]

    FIGURE F 101.2(10) ASBESTOS CEMENT TYPE B OR SINGLE-WALL METAL VENT SYSTEM SERVING TWO OR MORE DRAFT HOOD-EQUIPPED APPLIANCES

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

    times the common vent connector manifold inside diameter; that is, a 4 inch (102 mm) inside diameter common vent connector manifold should not exceed 72 inches (1829 mm) in length. [See Section 803.2.3]

    Note: This is an illustration of a typical manifolded vent connector. Different appliance, vent connector, or common vent types are possible. [See Section 803.2]

    FIGURE F 101.2(11) USE OF MANIFOLDED COMMON VENT CONNECTOR

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

  • CMC § 25.4 Medium relevance — show source text

    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 MATERIAL|LISTED TYPE L
    VENT MATERIAL|SINGLE-WALL
    METAL PIPE|FACTORY-BUILT
    CHIMNEY SECTIONS| |Listed appliance with draft hoods and appliance listed for use
    with Type B gas vents|As listed|As listed|6|As listed| |Residential boilers and furnaces with listed gas conversion
    burner and with draft hood|6|6|9|As listed| |Residential appliances listed for use with Type L vents|Not permitted|As listed|9|As listed| |Listed gas-fired toilets|Not permitted|As listed|As listed|As listed| |Unlisted residential appliances with draft hood|Not permitted|6|9|As listed| |Residential and low-heat appliance other than those above|Not permitted|9|18|As listed| |Medium-heat appliance|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.

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    CHIMNEYS AND VENTS

    withstanding the vent gas temperature produced by the appliance and of sufficient thickness to withstand physical damage. [NFPA 54:12.11.2.1]

    802.10.1.1 Unconditioned Space. Where the vent connector used for an appliance having a draft hood or a Category I appliance is located in or passes through an unconditioned space, attic, or crawl space, that portion of the vent connector shall be listed Type B, Type L, or listed vent material having equivalent insulation qualities.

    Exception: Single-wall metal pipe located within the exterior walls of the building and located in an unconditioned space other than an attic or a crawl space having a local 99 percent winter design temperature of 5°F (-15°C) or higher. {NFPA 54:12.11.2.2}

    802.10.1.2 Residential-Type Appliances. Vent connectors for residential-type appliances shall comply with the following:

    (1) Vent connectors for listed appliances having draft hoods, appliances having draft hoods and equipped with listed conversion burners, and Category I appliances that are not installed in attics, crawl spaces, or other unconditioned spaces shall be one of the following:

    (a) Type B or Type L vent material.

    (b) Galvanized sheet steel not less than 0.018 of an inch (0.457 mm) thick.

    (c) Aluminum (1100 or 3003 alloy or equivalent) sheet not less than 0.027 of an inch (0.686 mm) thick.

    (d) Stainless steel sheet not less than 0.012 of an inch (0.305 mm) thick.

  • CMC § 101.2 Medium relevance — show source text

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    APPENDIX F

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    attached to a tile-lined masonry chimney.

    Notes:

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

    FIGURE F 101.2(9) MASONRY CHIMNEY SERVING TWO OR MORE APPLIANCES WITH SINGLE-WALL METAL VENT CONNECTORS

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

    draft hood-equipped appliances. [See Table 803.2(5)]

    FIGURE F 101.2(10) ASBESTOS CEMENT TYPE B OR SINGLE-WALL METAL VENT SYSTEM SERVING TWO OR MORE DRAFT HOOD-EQUIPPED APPLIANCES

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

    times the common vent connector manifold inside diameter; that is, a 4 inch (102 mm) inside diameter common vent connector manifold should not exceed 72 inches (1829 mm) in length. [See Section 803.2.3]

    Note: This is an illustration of a typical manifolded vent connector. Different appliance, vent connector, or common vent types are possible. [See Section 803.2]

    FIGURE F 101.2(11) USE OF MANIFOLDED COMMON VENT CONNECTOR

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

    Note: This is an illustration of a typical offset vent. Different appliance, vent connector, or vent types are possible. [See Section 803.1 and Section 803.2]

    FIGURE F 101.2(12) USE OF OFFSET COMMON VENT

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

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    APPENDIX F

    inch (127 mm) diameter vent has an adjusted capacity of only 110 000 Btu/h (32 kW). In this case, the vent system must be increased to 6 inches (152 mm) in diameter. See the following calculations:

    122 000 Btu/h (35.7 kW) x 0.90 = 110 000 Btu/h (32 kW) for 5 inch (127 mm) vent

    From Table 803.1.2(2), select 6 inches (152 mm) vent.

    186 000 Btu/h (54.5 kW) x 0.90 = 167 000 Btu/h (49 kW)

    This figure is greater than the required 120 000 Btu/h (35 kW). Therefore, use a 6 inch (152 mm) vent and connector where three elbows are used. [NFPA 54:F.1.1]

    » FIGURE F 101.2(13) and combined input of

    MULTISTORY GAS VENT DESIGN PROCEDURE FOR EACH SEGMENT OF SYSTEM

    » F 101.3 Example 1: Single Draft Hood-Equipped

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  • CMC § 803.1 Medium relevance — show source text

    Note: This is an illustration of a typical offset vent. Different appliance, vent connector, or vent types are possible. [See Section 803.1 and Section 803.2]

    FIGURE F 101.2(12) USE OF OFFSET COMMON VENT

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

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    APPENDIX F

    inch (127 mm) diameter vent has an adjusted capacity of only 110 000 Btu/h (32 kW). In this case, the vent system must be increased to 6 inches (152 mm) in diameter. See the following calculations:

    122 000 Btu/h (35.7 kW) x 0.90 = 110 000 Btu/h (32 kW) for 5 inch (127 mm) vent

    From Table 803.1.2(2), select 6 inches (152 mm) vent.

    186 000 Btu/h (54.5 kW) x 0.90 = 167 000 Btu/h (49 kW)

    This figure is greater than the required 120 000 Btu/h (35 kW). Therefore, use a 6 inch (152 mm) vent and connector where three elbows are used. [NFPA 54:F.1.1]

    » FIGURE F 101.2(13) and combined input of

    MULTISTORY GAS VENT DESIGN PROCEDURE FOR EACH SEGMENT OF SYSTEM

    » F 101.3 Example 1: Single Draft Hood-Equipped

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    FIGURE F 101.2(13) MULTISTORY GAS VENT DESIGN PROCEDURE FOR EACH SEGMENT OF SYSTEM

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

    F 101.3 Example 1: Single Draft Hood-Equipped Appliance. An installer has a 120 000 British thermal units per hour (Btu/h) (35 kW) input appliance with a 5 inch (127 mm) diameter draft hood outlet that needs to be vented into a 10 foot (3048 mm) high Type B vent system. What size vent should be used assuming: (1) a 5 foot (1524 mm) lateral single-wall metal vent connector is used with two 90 degree (1.57 rad) elbows or (2) a 5 foot (1524 mm) lateral singlewall metal vent connector is used with three 90 degree (1.57 rad) elbows in the vent system? (See Figure F 101.3)

    Solution:

    Table 803.1.2(2) should be used to solve this problem because single-wall metal vent connectors are being used with a Type B vent, as follows:

    (1) Read down the first column in Table 803.1.2(2) until the row associated with a 10 foot (3048 mm) height and 5 foot (1524 mm) lateral is found. Read across this row until a vent capacity greater than 120 000 Btu/h (35 kW) is located in the shaded columns labeled NAT Max for

    draft hood-equipped appliances. In this case, a 5 inch (127 mm) diameter vent has a capacity of 122 000 Btu/h (35.7 kW) and can be used for this application.

  • CMC § 101.2 Medium relevance — show source text

    Notes:

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

    FIGURE G 101.2(8) MASONRY CHIMNEY SERVING TWO OR MORE APPLIANCES

    WITH TYPE B DOUBLE-WALL VENT CONNECTORS

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

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    APPENDIX G

    Table 510.2(4) is used when sizing single-wall metal vent connectors attached to a tile-lined masonry chimney.

    Notes:

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

    FIGURE G 101.2(9) MASONRY CHIMNEY SERVING TWO OR MORE APPLIANCES

    WITH SINGLE-WALL METAL VENT CONNECTORS

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

    Asbestos cement Type B or single-wall metal pipe vent serving two or more draft hood-equipped appliances. [See Table 510.2(5)]

    FIGURE G 101.2(10) ASBESTOS CEMENT TYPE B OR SINGLE-WALL

    METAL VENT SYSTEM SERVING TWO OR MORE

    DRAFT HOOD-EQUIPPED APPLIANCES

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

    Example: Manifolded common vent connector LM can be no greater than 18 times the common vent connector manifold inside diameter; that is, a 4 inch (102 mm) inside diameter common vent connector manifold should not exceed 72 inches (1829 mm) in length. [See Section 510.2.3]

    Note: This is an illustration of a typical manifolded vent connector. Different appliance, vent connector, or common vent types are possible. [See Section 510.2]

    FIGURE G 101.2(11) USE OF MANIFOLDED COMMON VENT CONNECTOR

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

    Example: Offset common vent

    Note: This is an illustration of a typical offset vent. Different appliance, vent connector, or vent types are possible. [See Section 510.1 and Section 510.2]

    FIGURE G 101.2(12) USE OF OFFSET COMMON VENT

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

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    APPENDIX G

    FIGURE G 101.2(13) MULTISTORY GAS VENT DESIGN PROCEDURE

    FOR EACH SEGMENT OF SYSTEM

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

  • CMC § 803.2 Medium relevance — show source text

    Furnace Vent Connector Diameter. Using the Vent Connector Capacity portion of Table 803.2(4), read down the Total Vent Height ( H ) column to 30 feet (9144 mm) and across the 3 feet (914 mm) Connector Rise ( R ) row. Because the furnace has a fan-assisted combustion system, find the first FAN Max column with a Btu/h rating greater than the furnace input rating. The 4 inch (102 mm) vent connector has a maximum input rating of 127 000 Btu/h (37 kW) and a minimum input rating of 95 000 Btu/h (27.8 kW). The 100 000 Btu/h (29 kW) furnace in this example falls within this range, so a 4 inch (102 mm) connector is adequate.

    Masonry Chimney. From Table F 102.3, the Equivalent Area for a Nominal Liner size of 8 inches (203 mm) by 12 inches (305 mm) is 63.6 square inches (0.041 m [2] ) . Using Table 803.2(4), Common Vent Capacity, read down the FAN + NAT column under the Minimum Internal Area of Chimney value of 63 to the row for 30 foot (9144 mm) height to find a capacity value of 739 000 Btu/h (217 kW). The combined input rating of the furnace and water heater, 135 000 Btu/h (40 kW), is less than the table value, so this is an acceptable installation.

    Section 803.2.17 requires the common vent area to be no greater than seven times the smallest listed appliance categorized vent area, flue collar area, or draft hood outlet area. Both appliances in this installation have 4 inch (102 mm) diameter outlets. From Table F 102.3, the equivalent area for an inside diameter of 4 inches (102 mm) is 12.2 square inches (0.008 m [2] ). Seven times 12.2 equals 85.4, which is greater than 63.6, so this configuration is acceptable. [NFPA 54:F.2.3] F 102.4 Example 5(c): Common Venting into an Exte- rior Masonry Chimney. In this case, the water heater and fan-assisted furnace of Examples 5(a) and 5(b) are to be common-vented into an exterior masonry chimney. The chimney height, clay-tile-liner dimensions, and vent connector heights and laterals are the same as in Example 5(b). This system is being installed in Charlotte, North Carolina. Does this exterior masonry chimney need to be relined? If so, what corrugated metallic liner size is recommended? What vent connector diameters are recommended? [See Table F 102.3 and Figure 803.1.2(6)]

    Solution:

    According to Section 803.2.20, Type B vent connectors are required to be used with exterior masonry chimneys. Use Table 803.2(8) and Table 803.2(9) to size FAN+NAT common venting installations involving Type-B double-wall connectors into exterior masonry chimneys.

    The local 99 percent winter design temperature needed to use Table 803.2(8) and Table 803.2(9) can be found in ASHRAE Handbook – Fundamentals. For Charlotte, North Carolina, this design temperature is 19°F (-7.2°C).

  • CMC § 101.0 Medium relevance — show source text

    2025 CALIFORNIA MECHANICAL CODE 533

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

    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.

    »

    »»

    »

    »

    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)]

    «

    «

    «

    2025 CALIFORNIA MECHANICAL CODE 535

  • CMC § 510.2.3 Medium relevance — show source text

    METAL VENT SYSTEM SERVING TWO OR MORE

    DRAFT HOOD-EQUIPPED APPLIANCES

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

    Example: Manifolded common vent connector LM can be no greater than 18 times the common vent connector manifold inside diameter; that is, a 4 inch (102 mm) inside diameter common vent connector manifold should not exceed 72 inches (1829 mm) in length. [See Section 510.2.3]

    Note: This is an illustration of a typical manifolded vent connector. Different appliance, vent connector, or common vent types are possible. [See Section 510.2]

    FIGURE G 101.2(11) USE OF MANIFOLDED COMMON VENT CONNECTOR

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

    Example: Offset common vent

    Note: This is an illustration of a typical offset vent. Different appliance, vent connector, or vent types are possible. [See Section 510.1 and Section 510.2]

    FIGURE G 101.2(12) USE OF OFFSET COMMON VENT

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

    2025 CALIFORNIA PLUMBING CODE 427

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

    APPENDIX G

    FIGURE G 101.2(13) MULTISTORY GAS VENT DESIGN PROCEDURE

    FOR EACH SEGMENT OF SYSTEM

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

    G 101.3 Example 1: Single Draft Hood-Equipped Appliance. An installer has a 120 000 British thermal units per hour (Btu/h) (35 kW) input appliance with a 5 inch (127 mm) diameter draft hood outlet that needs to be vented into a 10 foot (3048 mm) high Type B vent system. What size vent shall be used assuming: (1) a 5 foot (1524 mm) lateral single-wall metal vent connector is used with two 90 degree (1.57 rad) elbows or (2) a 5 foot (1524 mm) lateral singlewall metal vent connector is used with three 90 degree (1.57 rad) elbows in the vent system? (See Figure G 101.3)

    Solution:

    Table 510.1.2(2) should be used to solve this problem because single-wall metal vent connectors are being used with a Type B vent, as follows:

    (1) Read down the first column in Table 510.1.2(2) until the row associated with a 10 foot (3048 mm) height and 5 foot (1524 mm) lateral is found. Read across this row until a vent capacity greater than 120 000 Btu/h (35 kW) is located in the shaded columns labeled NAT Max for draft hood-equipped appliances. In this case, a 5 inch (127

    FIGURE G 101.2(14) PRINCIPLES OF DESIGN OF MULTISTORY VENTS USING

    VENT CONNECTOR AND COMMON VENT DESIGN TABLES

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

    mm) diameter vent has a capacity of 122 000 Btu/h (35.7 kW) and can be used for this application.

  • CMC § 16.7 Medium relevance — show source text

    Btu/h (9 kW), while a 4 inch (102 mm) vent connector has a maximum input of 57 000 Btu/h (16.7 kW). A 4 inch (102 mm) vent connector must therefore be used.

    Furnace Vent Connector Diameter. Using the Vent Connector Capacity portion of Table 510.2(4), read down the Total Vent Height ( H ) column to 30 feet (9144 mm) and across the 3 feet (914 mm) Connector Rise ( R ) row. Because the furnace has a fan-assisted combustion system, find the first FAN Max column with a Btu/h rating greater than the furnace input rating. The 4 inch (102 mm) vent connector has a maximum input rating of 127 000 Btu/h (37 kW) and a minimum input rating of 95 000 Btu/h (27.8 kW). The 100 000 Btu/h (29 kW) furnace in this example falls within this range, so a 4 inch (102 mm) connector is adequate.

    Masonry Chimney. From Table G 101.8, the equivalent area for a nominal liner size of 8 inches (203 mm) by 12 inches (305 mm) is 63.6 square inches (0.041 m [2] ). Using Table 510.2(4), Common Vent Capacity, read down the FAN

    • NAT column under the Minimum Internal Area of Chim ney value of 63 to the row for 30 foot (9144 mm) height to find a capacity value of 739 000 Btu/h (217 kW). The combined input rating of the furnace and water heater, 135 000 Btu/h (40 kW), is less than the table value, so this is an acceptable installation.

    Subsection 510.2.17 requires the common vent area to be no greater than seven times the smallest listed appliance categorized vent area, flue collar area, or draft hood outlet area. Both appliances in this installation have 4 inch (102 mm) diameter outlets. From Table G 101.8, the equivalent area for an inside diameter of 4 inches (102 mm) is 12.2 square inches (0.008 m [2] ). Seven times 12.2 equals 85.4, which is greater than 63.6, so this configuration is acceptable.

    [NFPA 54:F.2.3]

    G 101.9 Example 5(c): Common Venting into an Exte- rior Masonry Chimney. In this case, the water heater and fan-assisted furnace of Examples 5(a) and 5(b) are to be common-vented into an exterior masonry chimney. The chimney height, clay-tile-liner dimensions, and vent connector heights and laterals are the same as in Example 5(b). This system is being installed in Charlotte, North Carolina. Does this exterior masonry chimney need to be relined? If so, what corrugated metallic liner size is recommended? What vent connector diameters are recommended? (See Table G 101.8 and Figure 510.1.10)

    Solution:

    According to Section 510.2.20, Type B vent connectors are required to be used with exterior masonry chimneys. Use Table 510.2(8) and Table 510.2(9) to size FAN+NAT common venting installations involving Type B double-wall connectors into exterior masonry chimneys.

  • CMC § 803.2 Medium relevance — show source text
    • NA: Not applicable.

    2025 CALIFORNIA MECHANICAL CODE 189

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

    CHIMNEYS AND VENTS

    TABLE 803.2(3) MASONRY CHIMNEY [NFPA 54: TABLE 13.2(c)] (continued) *****

    Col1 Col2 Col3 NUMBER OF APPLIANCES: Col5 Col6 Col7 TWO OR MORE Col9 Col10 Col11
    APPLIANCE TYPE: APPLIANCE TYPE: APPLIANCE TYPE: APPLIANCE TYPE: ** CATEGORY I** ** CATEGORY I** ** CATEGORY I** ** CATEGORY I**
    APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: ** TYPE B DOUBLE-WALL CONNECTOR** ** TYPE B DOUBLE-WALL CONNECTOR** ** TYPE B DOUBLE-WALL CONNECTOR** ** TYPE B DOUBLE-WALL CONNECTOR**
    VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY
    TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)
    8 8 8 9 9 9 10 10 10
    APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR **APPLIANCE INPUT RATING LIMITS IN
  • CMC § 25.4 Medium relevance — show source text

    For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m [2]

    184 2025 CALIFORNIA MECHANICAL CODE

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

    CHIMNEYS AND VENTS

    TABLE 803.2(1) TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(a)] (continued) *****

    Col1 Col2 Col3 Col4 Col5 NUMBER OF APPLIANCES: Col7 Col8 Col9 TWO OR MORE Col11 Col12 Col13 Col14
    APPLIANCE TYPE: APPLIANCE TYPE: APPLIANCE TYPE: APPLIANCE TYPE: ** CATEGORY I** ** CATEGORY I** ** CATEGORY I** ** CATEGORY I** ** CATEGORY I**
    APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: ** TYPE B DOUBLE-WALL CONNECTOR** ** TYPE B DOUBLE-WALL CONNECTOR** ** TYPE B DOUBLE-WALL CONNECTOR** ** TYPE B DOUBLE-WALL CONNECTOR** ** TYPE B DOUBLE-WALL CONNECTOR**
    VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY
    TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) *TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –***D
  • California Mechanical Code Medium relevance — show source text

    OF APPLIANCES:|NUMBER OF APPLIANCES:|NUMBER OF APPLIANCES:|NUMBER OF APPLIANCES:|NUMBER OF APPLIANCES:|NUMBER OF APPLIANCES:| TWO OR MORE**|** TWO OR MORE**|** TWO OR MORE**|** TWO OR MORE**|** TWO OR MORE**|** TWO OR MORE**| ||||||APPLIANCE TYPE:|APPLIANCE TYPE:|APPLIANCE TYPE:|APPLIANCE TYPE:|APPLIANCE TYPE:|APPLIANCE TYPE:|** CATEGORY I**|** CATEGORY I**|** CATEGORY I**|** CATEGORY I**|** CATEGORY I**|** CATEGORY I**| ||||||APPLIANCE VENT CONNECTION:|APPLIANCE VENT CONNECTION:|APPLIANCE VENT CONNECTION:|APPLIANCE VENT CONNECTION:|APPLIANCE VENT CONNECTION:|APPLIANCE VENT CONNECTION:|** TYPE B DOUBLE-WALL CONNECTOR**|** TYPE B DOUBLE-WALL CONNECTOR**|** TYPE B DOUBLE-WALL CONNECTOR**|** TYPE B DOUBLE-WALL CONNECTOR**|** TYPE B DOUBLE-WALL CONNECTOR**|** TYPE B DOUBLE-WALL CONNECTOR**| |||VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY|VENT CONNECTOR CAPACITY| |||TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –****D (inch)|*TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER –***D

  • CMC § 803.2 Medium relevance — show source text
    • NA: Not applicable.

    2025 CALIFORNIA MECHANICAL CODE 185

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

    CHIMNEYS AND VENTS

    TABLE 803.2(1) TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(a)] (continued) *****

    Col1 Col2 Col3 NUMBER OF APPLIANCES: Col5 Col6 Col7 TWO OR MORE Col9 Col10 Col11
    APPLIANCE TYPE: APPLIANCE TYPE: APPLIANCE TYPE: APPLIANCE TYPE: ** CATEGORY I** ** CATEGORY I** ** CATEGORY I** ** CATEGORY I**
    APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: ** TYPE B DOUBLE-WALL CONNECTOR** ** TYPE B DOUBLE-WALL CONNECTOR** ** TYPE B DOUBLE-WALL CONNECTOR** ** TYPE B DOUBLE-WALL CONNECTOR**
    VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY
    TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch)
    20 20 20 22 22 22 24 24 24
    APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR **APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER
  • CMC § 25.4 Medium relevance — show source text

    configurations|

    For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m [2], °C = (°F-32)/1.8

    Notes: 1 See Figure 803.1.2(6) for a map showing local 99 percent winter design temperatures in the United States. 2 NA: Not applicable.

    182 2025 CALIFORNIA MECHANICAL CODE

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

    CHIMNEYS AND VENTS

    TABLE 803.2(1) TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(a)] *****

    Col1 Col2 Col3 Col4 Col5 NUMBER OF APPLIANCES: Col7 Col8 Col9 Col10 Col11 TWO OR MORE Col13 Col14 Col15 Col16 Col17
    APPLIANCE TYPE: APPLIANCE TYPE: APPLIANCE TYPE: APPLIANCE TYPE: APPLIANCE TYPE: APPLIANCE TYPE: CATEGORY I CATEGORY I CATEGORY I CATEGORY I CATEGORY I CATEGORY I
    APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: APPLIANCE VENT CONNECTION: TYPE B DOUBLE-WALL CONNECTOR TYPE B DOUBLE-WALL CONNECTOR TYPE B DOUBLE-WALL CONNECTOR TYPE B DOUBLE-WALL CONNECTOR TYPE B DOUBLE-WALL CONNECTOR TYPE B DOUBLE-WALL CONNECTOR
    VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY VENT CONNECTOR CAPACITY
    TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch) *TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –***D

Frequently asked questions

What’s the difference between a vent and a vent connector?

A Vent is the listed factory‑made conduit assembly that runs to outdoors; a Vent Connector is the short connection from the appliance draft hood or flue collar to that vent and is installed inside the appliance space (§ 224.0) — .

Can I use single‑wall connector through an attic?

Not unless the connector portion in the attic is Type B, Type L, or listed with equivalent insulation qualities; there is a limited exception for single‑wall in exterior walls when local 99% winter design temp is ≥ 5°F — § 802.10.1.1 — .

How high must a Type B vent terminate above the highest appliance?

A Type B (and Type L) vent shall terminate at least 5 ft (1524 mm) vertical height above the highest connected appliance draft hood or flue collar; Type B‑W has a 12 ft (3658 mm) rule for wall furnaces — § 802.6.1(2)–(3) — .

Are I allowed to fasten through the inner wall of a double‑wall vent?

No. Screws, rivets, and other fasteners shall not penetrate the inner wall of double‑wall gas vents except at the transition from the draft hood, flue collar, or single‑wall connector — § 802.6(4) — .

How do I size a vent connector for a 120,000 Btu/h appliance?

Use the appropriate § 803 table for the vent type and connector (for the common scenario of a 10 ft Type B vent and a 5 ft single‑wall connector with two elbows, the Appendix example shows a 5‑inch vent is acceptable) — see Appendix F and Table 803.1.2(2) — .

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