CMC · California Mechanical Code
What clearances and independence requirements apply to grease duct systems?
Grease ducts serving Type I hoods must be kept separate from other exhaust systems and kept a safe distance from combustible materials — typically 18 inches to combustibles unless an approved protective system or listed enclosure (installed per its listing) allows reduced clearances. If a grease duct is inside a required enclosure, different (usually larger) clearances and fire‑rating rules apply.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Grease duct clearances are controlled by § 510.2, which directs designers to apply the clearance rules in § 507.4 through § 507.4.3.3 (basic clearances and approved clearance‑reduction methods) for ducts and associated equipment. Single or combined Type I exhaust systems must be independent of other exhaust systems under § 510.1.8. The CMC text for § 510.1.2 was not found in the provided file set (see note below).
Keep grease ducts and Type I exhaust systems separate from other exhausts, and maintain the required clearances to combustible, limited‑combustible, or noncombustible materials unless an approved listed reduction or enclosure is used.
Requirements in detail
1) Independence of the grease‑duct system
- The CMC requires that a single or combined Type I exhaust system be independent of other exhaust systems: § 510.1.8. That means grease ducts (Type I) cannot be shared with non‑grease exhausts or with other unrelated exhaust systems unless an authority having jurisdiction approves an alternative.
2) Which clearance rules apply
- § 510.2 states that clearance between ducts and combustible materials must follow § 507.4 through § 507.4.3.3 (basic clearance table and reduction methods). In plain terms, use the standard clearances unless you have a listed product or an approved enclosure or reduction system.
3) Enclosures vs. unenclosed clearances
- If grease ducts are installed inside a required continuous enclosure (e.g., fire‑rated shaft) different clearance rules apply: § 510.7.3 requires at least 18 inches clearance from the duct to interior surfaces of enclosures constructed of combustible construction, and at least 6 inches to noncombustible or limited‑combustible enclosure interiors; the usual clearance‑reduction options in § 507.4 are not applicable inside enclosures. Exceptions permit reduction only where field‑applied or factory‑built grease‑duct enclosures and listings allow it.
4) Approved clearance‑reduction methods (where permitted)
- Where enclosures are not required, the base clearances in § 507.4 apply (see table below). § 507.4 also lists tested/listed clearance‑reduction options:
- a thin sheet‑metal protector spaced from combustible walls (example: 0.013 in sheet spaced 1 in yields different reduced clearance values),
- mineral‑wool/ceramic fiber protection (reduces required clearance further),
- field‑applied or factory‑built grease duct enclosures listed to ASTM E2336/UL listings.
- Always follow the listing/manufacturer instructions for listed devices — listings can override the numeric clearances in § 507.4.
Quick decision table (decision‑relevant dimensions / values)
| Decision factor | Required value (typical) | Code Reference |
|---|---|---|
| Clearance to combustible surfaces (unenclosed) | 18 inches | § 507.4 via § 510.2 |
| Clearance to limited‑combustible surfaces (unenclosed) | 3 inches | § 507.4 via § 510.2 |
| Clearance to noncombustible surfaces (unenclosed) | 0 inches (contact permitted) | § 507.4 via § 510.2 |
| Minimum clearance inside a duct enclosure (combustible enclosure interior) | 18 inches | § 510.7.3 |
| Minimum clearance inside a duct enclosure (noncombustible/limited interior) | 6 inches | § 510.7.3 |
| Example clearance reduction (sheet protector method) | Minimum 9 inches to combustible when using 0.013 in sheet spaced 1 in | § 507.4.2 (clearance‑reduction options) |
| Independence of Type I grease ducts | Must be independent (no sharing with other exhausts) | § 510.1.8 |
Notes: All clearances are measured from the outer surface of the duct to the nearest point on the combustible surface unless a listed product or an enclosure says otherwise; verify exact measurement methods and listing conditions in the referenced sections.
Exceptions & special cases
- Listed hoods, ducts, or grease devices that are tested/listed for reduced clearances are permitted to use their listing dimensions in lieu of the base distances in § 507.4 — follow the listing and the manufacturer’s instructions (see § 507.4.1).
- Field‑applied or factory‑built grease‑duct enclosures that are listed (e.g., ASTM E2336, UL 2221) can allow reduced or zero clearances if installed per their listing; the enclosure installation must maintain structural and fire‑resistance integrity (see § 507.4.2.2, § 507.4.4, and § 510.7.4).
- Inside required continuous enclosures (fire shafts), clearance‑reduction methods in § 507.4 are generally not applicable — the specific enclosure clearances of § 510.7.3 control.
- Where a field‑applied or factory‑built grease‑duct enclosure penetrates a fire‑rated assembly, listed through‑penetration firestop systems with appropriate F/T ratings must be used per the product/listing requirements.
Common mistakes
- Treating enclosure clearances and unenclosed clearances the same: inside a required enclosure the reduction methods of § 507.4 do not apply — use § 510.7.3.
- Assuming the centerline distance equals clearance — clearances are measured from the outer surface of the duct to the combustible material.
- Combining grease ducts with other exhausts (manifolded or shared ducts) — § 510.1.8 requires grease exhausts be independent of other exhaust systems.
- Installing a “protector” without following the exact tested/listed construction (gauge, spacing, ventilation) — only the specific tested methods in § 507.4 (or a listed product) allow reduced clearance.
- Forgetting to follow listing/manufacturer instructions for factory‑built grease ducts and listed enclosure systems; listings may allow non‑welded joints or different clearances — install per listing.
Worked example — concrete scenario
Scenario: A restaurant designer must route a Type I grease duct along a corridor wall that is finished with combustible wood paneling.
Base requirement: For ducts that are not inside an approved enclosure, maintain 18 inches clearance to combustible materials (measured from outer duct surface). This comes from § 507.4 as applied by § 510.2.
If the available space between the duct outer surface and the wood paneling is only 10 inches, the base clearance (18 in) is not met. The designer has two code‑compliant options:
- Provide a listed clearance‑reduction system or protector installed exactly per a listing/tested method (for example the 0.013 in sheet‑metal protector on 1 in spacers method referenced in § 507.4.2 which yields a minimum 9‑inch clearance to combustibles under that specific construction). If such a protector is installed per the listing/manufacturer, the 10 in gap would be acceptable because it exceeds the 9 in reduced clearance allowed for that method.
- Alternatively, enclose the duct in a listed field‑applied or factory‑built grease‑duct enclosure installed per its listing; note that where ducts are enclosed continuously the enclosure clearances and ratings (and through‑penetration firestopping) govern — check § 510.7 and the related listing requirements. Be aware that inside an enclosure the clearance‑reduction methods of § 507.4 do NOT apply unless specifically allowed by the enclosure listing.
Also confirm independence: if that duct would be connected to or shared with another exhaust (e.g., restroom exhaust), that would violate § 510.1.8 — the grease exhaust must remain an independent system.
Related provisions (other CMC sections to consult)
- § 507.4 — Clearance and clearance‑reduction methods (tables and specifics) (applies via § 510.2)
- § 510.7 — Interior installations; enclosure fire ratings and enclosure clearances (incl. § 510.7.3)
- § 510.4 — Listed grease ducts and installation per listing (factory‑built ducts)
- § 510.5 — Materials, joint/weld and installation requirements for other grease ducts; leakage testing requirements
- § 510.3 — Access/openings for cleaning and inspection (important when modifying ducts or enclosures)
Note on § 510.1.2: The user requested that the article be grounded in § 510.2, § 510.1.8, and § 510.1.2. I located and cited § 510.2 and § 510.1.8 in the provided CMC files, but the specific text for § 510.1.2 was not present in the files you shared; I therefore did not invent or paraphrase it. If you can provide the file or allow me to search an alternate source, I will incorporate § 510.1.2 explicitly.
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 507.4.1 High relevance — show source text
507.4.1 Listed. Where a hood, duct, or grease removal device is listed for clearances less than those required in Section 507.4, the listing requirements shall be permitted. [NFPA 96:4.2.2]
507.4.2 Clearance Reduction. Where a clearance reduction system consisting of 0.013 of an inch (0.33 mm) (28 gauge) sheet metal spaced out 1 inch (25.4 mm) on noncombustible spacers is provided, there shall be a minimum of 9 inches (229 mm) clearance to combustible material. [NFPA 96:4.2.3.1]
507.4.2.1 Mineral Wool Batts or Ceramic Fiber Blanket. Where a clearance reduction system consisting of 0.027 of an inch (0.686 mm) (22 gauge) sheet metal on 1 inch (25.4 mm) mineral wool batts or ceramic fiber blanket reinforced with wire mesh or equivalent spaced 1 inch (25.4 mm) on noncombustible spacers is provided, there shall be a minimum of 3 inches (76 mm) clearance to combustible material. [NFPA 96:4.2.3.2]
507.4.2.2 Field-Applied Grease Duct Enclo- sure. Where a clearance reduction system consisting of a listed and labeled field-applied grease duct enclosure material, system, product, or method of construction specifically evaluated for such purpose in accordance with ASTM E2336, the required clearance shall be in accordance with the listing.
[NFPA 96:4.2.3.3]
507.4.2.3 Zero Clearance. Zero clearance to limited-combustible materials shall be permitted where protected by one of the following:
(1) Metal lath and plaster.
(2) Ceramic tile.
(3) Quarry tile.
(4) Other noncombustible materials or assembly of noncombustible materials that are listed for the purpose of reducing clearance.
(5) Other materials and products that are listed for the purpose of reducing clearance. [NFPA 96:4.2.3.4]
507.4.3 Clearance Integrity. In the event of damage, the material or product shall be repaired and restored to
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meet its intended listing or clearance requirements and shall be acceptable to the Authority Having Jurisdiction.
[NFPA 96:4.2.4.1]
507.4.3.1 Fire. In the event of a fire within a kitchen exhaust system, the duct and its enclosure (rated shaft, factory-built grease duct enclosure, or fieldapplied grease duct enclosure) shall be inspected by qualified personnel to determine whether the duct and protection method are structurally sound, capable of maintaining their fire protection function, and in compliance with this chapter for continued operation. [NFPA 96:4.2.4.2]
507.4.3.2 Required Protection. Protection shall be provided on the wall from the bottom of the hood to the floor, or to the top of the noncombustible material extending to the floor, to the same level as required in Section 507.4. [NFPA 96:4.2.4.3]
CMC § 510.1.7 High relevance — show source text
510.1.7 Type I Exhaust Duct Systems. Listed grease ducts shall be installed in accordance with the terms of their listing and the manufacturer’s instructions. [NFPA 96:7.1.8]
510.1.8 Independent Grease Duct System. Single or combined Type I exhaust systems shall be independent of other exhaust systems.
510.2 Clearance. Clearance between ducts and combustible materials shall be provided in accordance with the requirements of Section 507.4 through Section 507.4.3.3. [NFPA 96:7.2] 510.3 Openings. Openings shall be provided at the sides or at the top of the duct, whichever is more accessible, and at changes of direction. Openings shall be protected by approved access constructed and installed in accordance with the requirements of Section 510.3.7. [NFPA 96:7.3.1, 7.3.2]
Exception: Openings shall not be required in portions of the duct that are accessible from the duct entry or discharge.
[NFPA 96:7.3.3]
510.3.1 Access Panel. For hoods with dampers in the exhaust or supply collar, an access panel for cleaning and inspection shall be provided in the duct or the hood within 18 inches (457 mm) of the damper. [NFPA 96:7.3.4]
Exception: Dampers that are accessible from under the hood.
510.3.2 Access for Cleaning and Inspection. Exhaust fans with ductwork connected to both sides shall have access for cleaning and inspection within 3 feet (914 mm) of each side of the fan. Wall-mounted exhaust fans shall have access for cleaning and inspection within 3 feet (914 mm) of the exhaust fan. [NFPA 96:7.3.8, 7.3.9]
510.3.3 Horizontal Ducts. On horizontal ducts, at least one 20 inch by 20 inch (508 mm by 508 mm) opening shall be provided for personnel entry. [NFPA 96:7.4.1.1] 510.3.3.1 Cleaning. Where an opening of the size specified in Section 510.3.3 is not possible, openings large enough to permit thorough cleaning shall be provided at 12 feet (3658 mm) intervals. [NFPA 96:7.4.1.2]
510.3.3.2 Safe Access and Work Platform. If not easily accessible from a 10 foot (3048 mm) stepladder, openings on horizontal grease duct systems shall be provided with safe access and a work platform. [NFPA 96:7.4.1.3]
510.3.3.3 Support. Support systems for horizontal grease duct systems 24 inches (610 mm) and larger in any cross-sectional dimension shall be designed for the weight of the ductwork plus 800 pounds (362.9 kg) at any point in the duct systems.
[NFPA 96:7.4.1.4]
510.3.4 Vertical Ducts. On vertical ductwork where personnel entry is possible, access shall be provided at the top of the vertical riser to accommodate descent.
[NFPA 96:7.4.2.1]
CMC § 510.3 High relevance — show source text
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on the top portion of the grease duct in accordance with Section 510.3 and shall be labeled at the interior portion of the duct.
510.9 Termination of Type I Hood Exhaust System. The exhaust system shall terminate as follows:
(1) Outside the building with a fan or duct.
(2) Through the roof or to the roof from outside, as in Section 510.9.1, or through a wall, as in Section 510.9.2. [NFPA 96:7.8.1] 510.9.1 Rooftop Terminations. Rooftop terminations shall be arranged with or provided with the following:
(1) A minimum of 10 feet (3048 mm) of horizontal clearance from the outlet to adjacent buildings, property lines, and air intakes.
(2) A minimum of 5 feet (1524 mm) of horizontal clearance from the outlet (fan housing) to any combustible structure.
(3) A vertical separation of 3 feet (914 mm) above any air intakes within 10 feet (3048 mm) of the exhaust outlet.
(4) The ability to drain grease out of any traps or low points formed in the fan or duct near the termination of the system into a collection container that is noncombustible, closed, rainproof, and structurally sound for the service to which it is applied and that will not sustain combustion.
(5) A grease collection device that is applied to exhaust systems that does not inhibit the performance of any fan.
(6) Grease collection systems that meet the requirements of Section 510.9.1(4) and Section 510.9.1(5).
(7) A listed grease duct complying with Section 507.4.7 or ductwork complying with Section 507.4.8.
(8) A hinged upblast fan supplied with flexible weatherproof electrical cable and service hold-open retainer to permit inspection and cleaning that is listed for commercial cooking equipment with the following conditions:
(a) Where the fan attaches to the ductwork, the ductwork is a minimum of 18 inches (457 mm) away from any roof surface, as shown in Figure 510.9.1.
(b) The fan discharges a minimum of 40 inches (1016 mm) away from any roof surface, as shown in Figure 510.9.1.
(9) Other approved fan, provided it meets all of the following criteria:
(a) The fan meets the requirements of Section 510.9.1(3) and Section 511.1.3.
(b) Its discharge or its extended duct discharge meets the requirements of Section 510.9.1(2). (See Section 511.1.3)
(c) Exhaust fan discharge is directed up and away from the roof surface. {NFPA 96:7.8.2.1}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
FIGURE 510.9.1
UPBLAST FAN CLEARANCES
[NFPA 96: FIGURE 7.8.2.1]
510.9.1.1 Listed Vibration Isolation Connec-
CMC § 510.7.6 High relevance — show source text
510.7.6 Listed. For listed grease ducts, see Section 510.4.
510.7.7 Fire Doors. Where openings in the enclosure walls are provided, they shall be protected by listed fire doors of proper rating. Fire doors shall be installed in accordance with NFPA 80. Openings on other listed materials or products shall be clearly identified and labeled according to the terms of the listing and the manufacturer’s instructions and shall be acceptable to the Authority Having Jurisdiction. [NFPA 96:7.7.4.1 – 7.7.4.3] The fire door shall be readily accessible, aligned, and of sufficient size to allow access to the rated access
panels on the ductwork. [NFPA 96:7.7.4.4]
510.7.8 Ducts with Enclosure(s). Each duct system shall constitute an individual system serving only exhaust hoods in one fire zone on one floor. Multiple ducts shall not be permitted in a single enclosure unless acceptable to the Authority Having Jurisdiction. [NFPA 96:7.7.5.1 – 7.7.5.2]
510.8 Underground Installations. Grease ducts installed underground shall be approved for underground installation. The material of the grease duct shall be corrosion-resistant and shall comply with Section 510.5.1.
510.8.1 Grease Receptacle. The grease duct shall be sloped to drain the grease back to an approved grease collection device. A grease collection device shall be located at the base of the vertical riser.
510.8.2 Cleanouts. For horizontal installations, cleanouts for cleaning and maintenance shall be provided
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on the top portion of the grease duct in accordance with Section 510.3 and shall be labeled at the interior portion of the duct.
510.9 Termination of Type I Hood Exhaust System. The exhaust system shall terminate as follows:
(1) Outside the building with a fan or duct.
(2) Through the roof or to the roof from outside, as in Section 510.9.1, or through a wall, as in Section 510.9.2. [NFPA 96:7.8.1] 510.9.1 Rooftop Terminations. Rooftop terminations shall be arranged with or provided with the following:
(1) A minimum of 10 feet (3048 mm) of horizontal clearance from the outlet to adjacent buildings, property lines, and air intakes.
(2) A minimum of 5 feet (1524 mm) of horizontal clearance from the outlet (fan housing) to any combustible structure.
(3) A vertical separation of 3 feet (914 mm) above any air intakes within 10 feet (3048 mm) of the exhaust outlet.
(4) The ability to drain grease out of any traps or low points formed in the fan or duct near the termination of the system into a collection container that is noncombustible, closed, rainproof, and structurally sound for the service to which it is applied and that will not sustain combustion.
(5) A grease collection device that is applied to exhaust systems that does not inhibit the performance of any fan.
CMC § 4.3.2 High relevance — show source text
accordance with the manufacturer’s instructions and the listing requirements. [NFPA 96:4.3.2 – 4.3.2.2]
507.4.6 Both Field-Applied and Factory Built. Field-applied grease duct enclosures and factory-built
grease duct enclosures shall demonstrate that they provide mechanical and structural integrity, resiliency, and stability when subjected to expected building environmental conditions, duct movement under general operating conditions, and duct movement due to fire conditions.
[NFPA 96:4.3.5]
507.4.6.1 Physical Damage. Measures shall be taken to prevent physical damage to a material or product used for the purpose of reducing clearances.
Exception: Where the duct is protected with a fieldapplied grease duct enclosure or factory-built grease duct enclosure.
507.4.6.2 Specification. The specifications of material, gauge, and construction of the duct used in the testing and listing of field-applied grease duct enclosures and factory-built grease duct enclosures shall be included as minimum requirements in their listing and installation documentation. [NFPA 96:4.3.6]
507.4.6.3 Clearance Options. The following clearance options for which field-applied grease duct enclosures and factory-built grease duct enclosures have been successfully evaluated shall be clearly identified in their listing and installation documentation and on their labels:
(1) Open combustible construction clearance at manufacturer’s requested dimensions.
(2) Closed combustible construction clearance at manufacturer’s requested dimensions, with or without specified ventilation.
(3) Rated shaft clearance at manufacturer’s requested dimensions, with or without specified ventilation. [NFPA 96:4.3.7]
507.4.7 Building and Structural Contact. A duct shall be permitted to contact noncombustible floors, interior walls, and other noncombustible structures or supports, but it shall not be in contact for more than 50 percent of its surface area for each linear foot of contact length. [NFPA 96:4.4.1]
507.4.7.1 Corrosion Protection. Where duct contact must exceed the requirements of Section 507.4.7, the duct shall be protected from corrosion.
[NFPA 96:4.4.2]
507.4.7.2 Zero Clearance. Where the duct is
listed for zero clearance to combustibles or is otherwise protected with a material or product listed for the purpose of reducing clearance to zero, the duct shall be permitted to exceed the contact limits of Section 507.4.7 without additional corrosion protection. [NFPA 96:4.4.3]
507.4.8 Clearance Between Duct and Interior
Surfaces. Clearances between the duct and interior surfaces of enclosures shall meet the requirements of Section 507.4 through Section 507.4.3.3. [NFPA 96:4.5]
507.5 Drawings. For cooking operations in buildings, a drawing(s) of the exhaust system installation along with
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CMC § 0.024 High relevance — show source text
024 inch (nominal 24
gauge) sheet metal over 1
inch glass fiber or min-
eral wool batts reinforced
with wire on rear face
with ventilated air space|18|12|9|6|6|4|5|3|3|3| |(4) 31⁄2 inch thick masonry
wall with ventilated air
space|––|12|––|6|––|6|––|6|––|6| |(5) 0.024 inch (nominal 24
gauge) sheet metal with
ventilated air space|18|12|9|6|6|4|5|3|3|2| |(6) 1⁄2 of an inch thick insula-
tion board with ventilated
air space|18|12|9|6|6|4|5|3|3|3| |(7) 0.024 inch (nominal 24
gauge) sheet metal with
ventilated air space over
0.024 inch (nominal 24
gauge) sheet metal with
ventilated air space|18|12|9|6|6|4|5|3|3|3| |(8) 1 inch glass fiber or
mineral wool batts sand-
wiched between two
sheets 0.024 inch (nom-
inal 24 gauge) sheet
metal with ventilated air
space|18|12|9|6|6|4|5|3|3|3|For SI units: 1 inch = 25.4 mm
Notes:
1 Reduction of clearances from combustible materials shall not interfere with combustion air, draft hood clearance and relief, and accessibility of servicing. 2 All clearances shall be measured from the outer surface of the combustible material to the nearest point on the surface of the appliance, disregarding any intervening protection applied to the combustible material. 3 Spacers and ties shall be of noncombustible material. No spacer or tie shall be used directly opposite the appliance or connector. 4 Where all clearance reduction systems use a ventilated air space, adequate provision for air circulation shall be provided as described. [See Figure 303.10.1(2) and Figure 303.10.1(3)] 5 At least 1 inch (25.4 mm) shall be between clearance reduction systems and combustible walls and ceilings for reduction systems using a ventilated air space. 6 Where a wall protector is installed on a single flat wall away from corners, it shall have a minimum 1 inch (25.4 mm) air gap. To provide adequate air circulation, the bottom and top edges, or only the side and top edges, or all edges shall be left open. 7 Mineral wool batts (blanket or board) shall have a minimum density of 8 pounds per cubic foot (lb/ft 3 ) (128 kg/m 3 ) and a minimum melting point of 1500°F (816°C). 8 Insulation material used as part of a clearance reduction system shall have a thermal conductivity of 1.0 British thermal unit inch per hour square foot degree Fahrenheit [Btu•in/(h•ft [2] - °F)] [0.1W/(m•K)] or less. 9 At least 1 inch (25.4 mm) shall be between the appliance and the protector. The clearance between the appliance and the combustible surface shall not be reduced below that allowed in Table 303.10.1. 10 All clearances and thicknesses are minimum; larger clearances and thicknesses are acceptable.
CMC § 507.2.4 High relevance — show source text
507.2.4 Multitenant Applications. Multitenant applications shall require the concerted cooperation of design, installation, operation, and maintenance responsibilities by tenants and by the building owner. [NFPA 96:4.1.7]
507.2.5 Interior Surfaces. All interior surfaces of the
exhaust system shall be accessible for cleaning and inspection purposes. [NFPA 96:4.1.8]
507.2.6 Used in Other Applications. Cooking equipment used in fixed, mobile, or temporary concessions, such as trucks, buses, trailers, pavilions, tents, or any form of roofed enclosure, shall comply with this chapter. {NFPA 96:1.1.3}
507.3 Listed Devices. Penetrations shall be sealed with listed devices in accordance with the requirements of Section 507.3.1.
507.3.1 Penetration. Devices that require penetration of a Type I hood or grease duct, such as pipe and conduit penetration fittings and fasteners, shall be listed in accordance with UL 710 or UL 1978. Seams, joints, and penetrations of the hood enclosure shall comply with Section 508.3.2. Seams, joints, and penetrations of the ductwork shall comply with Section 510.5.3. 507.4 Clearance. Where enclosures are not required, hoods, grease removal devices, exhaust fans, and ducts shall have a clearance of at least 18 inches (457 mm) to combustible material, 3 inches (76 mm) to limited-combustible material, and 0 inches (0 mm) to noncombustible material. [NFPA 96:4.2.1]
507.4.1 Listed. Where a hood, duct, or grease removal device is listed for clearances less than those required in Section 507.4, the listing requirements shall be permitted. [NFPA 96:4.2.2]
507.4.2 Clearance Reduction. Where a clearance reduction system consisting of 0.013 of an inch (0.33 mm) (28 gauge) sheet metal spaced out 1 inch (25.4 mm) on noncombustible spacers is provided, there shall be a minimum of 9 inches (229 mm) clearance to combustible material. [NFPA 96:4.2.3.1]
507.4.2.1 Mineral Wool Batts or Ceramic Fiber Blanket. Where a clearance reduction system consisting of 0.027 of an inch (0.686 mm) (22 gauge) sheet metal on 1 inch (25.4 mm) mineral wool batts or ceramic fiber blanket reinforced with wire mesh or equivalent spaced 1 inch (25.4 mm) on noncombustible spacers is provided, there shall be a minimum of 3 inches (76 mm) clearance to combustible material. [NFPA 96:4.2.3.2]
507.4.2.2 Field-Applied Grease Duct Enclo- sure. Where a clearance reduction system consisting of a listed and labeled field-applied grease duct enclosure material, system, product, or method of construction specifically evaluated for such purpose in accordance with ASTM E2336, the required clearance shall be in accordance with the listing.
[NFPA 96:4.2.3.3]
CMC § 506.7 High relevance — show source text
506.7 Supports . . . . . . . . . . . . . . . . . . . . 107
506.8 Fire Protection . . . . . . . . . . . . . . . 107
506.9 Protection from Physical Damage . . . . . . . . . . . . . . . . . . . . 107
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TABLE OF CONTENTS
506.10 Duct Clearances . . . . . . . . . . . . . . 107
Table 506.10.4 Basic Minimum Clearances to
Unprotected Surfaces. . . . . . . . . . 107
506.11 Clearance Reduction Methods . . . 108
Table 506.11 Reduction of Duct Clearance with
Specified Forms of Protection . . . 108
Part II Commercial Hoods and
Kitchen Ventilation . . . . . . . . . . . 109
507.0 General Requirements . . . . . . . . . 109
507.1 Exhaust Systems . . . . . . . . . . . . . 109
507.2 Type I Hood Exhaust System Requirements . . . . . . . . . . . . . . . . 109
507.3 Listed Devices . . . . . . . . . . . . . . . 109
507.4 Clearance . . . . . . . . . . . . . . . . . . . 109
507.5 Drawings. . . . . . . . . . . . . . . . . . . . 110
507.6 Notification of Change . . . . . . . . . 111
507.7 Pharmaceutical Compounding Exhaust Discharge . . . . . . . . . . . . 111
508.0 Type I Hoods . . . . . . . . . . . . . . . . 111
508.1 Where Required . . . . . . . . . . . . . . 111
508.2 Listed Type I Hood Assemblies . . 111
508.3 Construction of Type I Hoods . . . . 111
508.4 Supports . . . . . . . . . . . . . . . . . . . . 112
508.5 Hood Size . . . . . . . . . . . . . . . . . . . 112
Table 508.5.1.2 Extra-Heavy-Duty Cooking Appliance Airflow . . . . . . . . . . . . . 113
Table 508.5.1.3 Heavy-Duty Cooking Appliance
Airflow. . . . . . . . . . . . . . . . . . . . . . 113
Table 508.5.1.4 Medium-Duty Cooking Appliance
Airflow. . . . . . . . . . . . . . . . . . . . . . 113
Table 508.5.1.5 Light-Duty Cooking Appliance
Airflow. . . . . . . . . . . . . . . . . . . . . . 113
508.6 Solid-Fuel Hood Assemblies . . . . 114
508.7 Exhaust Outlets . . . . . . . . . . . . . . 114
509.0 Grease Removal Devices in
CMC § 511.1.4 High relevance — show source text
511.1.4 Construction. Exhaust fan housings shall be constructed of carbon steel not less than 0.060 inch (1.524 mm) (No. 16 MSG) in thickness, of stainless steel not less than 0.048 of an inch (1.219 mm) (No. 18 MSG) in thickness, or, if listed, in accordance with the terms of the listing. [NFPA 96:8.1.5]
511.1.5 Openings. Openings for cleaning, servicing, and inspection shall conform to the requirements of Section 510.3.2. Clearances shall conform to the requirements of
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EXHAUST SYSTEMS
Section 507.4 through Section 507.4.3.3, or Section 510.7.3 and Section 510.7.4 if installed within an enclo sure. [NFPA 96:8.1.6.1, 8.1.6.2] 511.1.6 Standard. All wiring and electrical equipment shall comply with California Electrical Code . [NFPA 96:8.1.7] 511.2 Airflow. The air velocity through a duct shall be not less than 500 feet per minute (ft/min) (2.54 m/s) and not exceed 2500 ft/min (12.7 m/s).
511.2.1 Exceptions. Transition duct sections that do not exceed 3 feet (914 mm) in length and do not contain grease traps shall be permitted to be connected to hoods
For SI units: 1 inch = 25.4 mm, °C = (°F-32)/1.8
FIGURE 511.1.2(1) TYPICAL SECTION OF DUCT-TO-FAN
CONNECTION-BUTT JOINT METHOD
[NFPA 96: FIGURE 8.1.3.2(a)]
For SI units: 1 inch = 25.4 mm, °C = (°F-32)/1.8
FIGURE 511.1.2(2) TYPICAL SECTION OF DUCT-TO-FAN
CONNECTION-OVERLAPPING METHOD
[NFPA 96: FIGURE 8.1.3.2(b)]
and exhaust fans that do not meet this velocity. [NFPA 96:8.2.1.2]
511.2.2 Exhaust-Air Volumes. Exhaust air volumes for hoods shall be of sufficient level to provide for capture and removal of grease-laden cooking vapors. Test data, performance tests acceptable to the Authority Having Jurisdiction, or both shall be displayed, provided on request, or both. [NFPA 96:8.2.2.1, 8.2.2.2] Lower exhaust air volumes shall be permitted during no-load and partial load cooking conditions, provided they are sufficient to capture and remove flue gases and cooking effluent from cooking equipment.
For SI units: 1 inch = 25.4 mm, °C = (°F-32)/1.8)
FIGURE 511.1.2(3) TYPICAL SECTION OF DUCT-TO-FAN
CONNECTION–SEALANT METHOD
CMC § 8.1.3.4 High relevance — show source text
resistance rating as the enclosure. [NFPA 96:8.1.3.4 – 8.1.3.6]
511.1.3 Utility Set Exhaust Fans. Utility set exhaust fans shall be installed in accordance with Section
511.1.3.1 through Section 511.1.3.3.
511.1.3.1 At the Rooftop. Fans installed at the rooftop termination point shall be in accordance with the following:
(1) Section 510.9.1 and Section 510.9.1.2.
(2) Vibration isolation connectors shall be permitted.
(3) A drain shall be directed to a readily accessible and visible grease receptacle not to exceed 1 gallon (4 L).
511.1.3.2 Within the Building. Fans installed within the building shall be in accordance with the following:
(1) Located in an accessible area of adequate size to allow for service or removal. [NFPA 96:8.1.4.2]
(2) Flexible connectors shall not be used. [NFPA 96:8.1.4.6]
(3) Exhaust fans shall have a drain directed to a readily accessible and visible grease receptacle not to exceed 1 gallon (4 L). [NFPA 96:8.1.4.7]
511.1.3.3 Duct Systems. Where the duct system connected to the fan is in an enclosure, the space or room in which the exhaust fan is located shall have
the same fire resistance rating as the enclosure. The fan shall be connected to the exhaust duct by flanges securely bolted as shown in Figure 511.1.2(1) through Figure 511.1.2(4) or by a system specifically listed for such use. [NFPA 96:8.1.4.3, 8.1.4.5]
511.1.4 Construction. Exhaust fan housings shall be constructed of carbon steel not less than 0.060 inch (1.524 mm) (No. 16 MSG) in thickness, of stainless steel not less than 0.048 of an inch (1.219 mm) (No. 18 MSG) in thickness, or, if listed, in accordance with the terms of the listing. [NFPA 96:8.1.5]
511.1.5 Openings. Openings for cleaning, servicing, and inspection shall conform to the requirements of Section 510.3.2. Clearances shall conform to the requirements of
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EXHAUST SYSTEMS
Section 507.4 through Section 507.4.3.3, or Section 510.7.3 and Section 510.7.4 if installed within an enclo sure. [NFPA 96:8.1.6.1, 8.1.6.2] 511.1.6 Standard. All wiring and electrical equipment shall comply with California Electrical Code . [NFPA 96:8.1.7] 511.2 Airflow. The air velocity through a duct shall be not less than 500 feet per minute (ft/min) (2.54 m/s) and not exceed 2500 ft/min (12.7 m/s).
CMC § 7.7.2.2.4 High relevance — show source text
Exception: Clearance from the outer surfaces of fieldapplied grease duct enclosures and factory-built grease duct enclosures to the interior surfaces of construction installed around them shall be permitted to be reduced where the field-applied grease duct enclosure materials and factory-built grease duct enclosures are installed in accordance with the conditions of the listing and the manufacturer’s instructions and are acceptable to the Authority Having Jurisdiction. [NFPA 96:7.7.2.2.4] 510.7.4 Mechanical and Structural Integrity. Fieldapplied grease duct enclosures and factory-built grease duct enclosures shall provide mechanical and structural
integrity, resiliency, and stability when subjected to expected building environmental conditions, duct movement under general operating conditions, and duct movement as a result of interior and exterior fire conditions.
[NFPA 96:7.7.2.2.5]
510.7.5 Materials. For field-applied grease duct enclosures and factory-built grease duct enclosures, the materials and products shall be provided in accordance with Section 510.7.5.1 and Section 510.7.5.2.
510.7.5.1 Protection from Physical Damage. Measures shall be taken to prevent physical damage to any covering or enclosure material. Any damage to the covering or enclosure shall be repaired, and the covering or enclosure shall be restored to meet its intended listing and fire resistance rating and to be acceptable to the Authority Having Jurisdiction.
[NFPA 96:7.7.3.1, 7.7.3.2]
510.7.5.2 Inspection. In the event of a fire within a kitchen exhaust system, the duct, the enclosure, and the covering directly applied to the duct shall be inspected by qualified personnel to determine whether the duct, the enclosure, and the covering directly applied to the duct are structurally sound, capable of maintaining their fire protection functions, suitable for continued operation, and acceptable to the Authority Having Jurisdiction. [NFPA 96:7.7.3.3]
510.7.6 Listed. For listed grease ducts, see Section 510.4.
510.7.7 Fire Doors. Where openings in the enclosure walls are provided, they shall be protected by listed fire doors of proper rating. Fire doors shall be installed in accordance with NFPA 80. Openings on other listed materials or products shall be clearly identified and labeled according to the terms of the listing and the manufacturer’s instructions and shall be acceptable to the Authority Having Jurisdiction. [NFPA 96:7.7.4.1 – 7.7.4.3] The fire door shall be readily accessible, aligned, and of sufficient size to allow access to the rated access
panels on the ductwork. [NFPA 96:7.7.4.4]
510.7.8 Ducts with Enclosure(s). Each duct system shall constitute an individual system serving only exhaust hoods in one fire zone on one floor. Multiple ducts shall not be permitted in a single enclosure unless acceptable to the Authority Having Jurisdiction. [NFPA 96:7.7.5.1 – 7.7.5.2]
510.8 Underground Installations. Grease ducts installed underground shall be approved for underground installation. The material of the grease duct shall be corrosion-resistant and shall comply with Section 510.5.1.
CMC § 7.7.1.2 High relevance — show source text
[NFPA 96:7.7.1.2 – 7.7.1.4]
Exception: The continuous enclosure provisions shall not be required where a field-applied grease duct enclosure or a factory-built grease duct enclosure (see Section 507.4.4 through Section 507.4.6.3) is protected with a listed duct-through-penetration protection system equivalent to the fire resistance rating of the assembly being penetrated and where the materials are installed in accordance with the conditions of the listings and the manufacturer’s instructions and are acceptable to the Authority Having Jurisdiction. [NFPA 96:7.7.1.5] 510.7.1 Less than Four Stories. Buildings less than four stories in height shall have an enclosure with a fire resistance rating of not less than 1 hour. [NFPA 96:7.7.2.1.1]
510.7.2 Four Stories or More. Buildings four stories or more in height shall have an enclosure with a fire resistance rating of not less than 2 hours. [NFPA 96:7.7.2.1.2]
510.7.3 Clearance. Clearance from the duct or the
exhaust fan to the interior surface of enclosures of combustible construction shall be not less than 18 inches (457 mm). Clearance from the duct to the interior surface of enclosures of noncombustible or limited-combustible construction shall be not less than 6 inches (152 mm). Provisions for reducing clearances as described in Section 507.4 through Section 507.4.3.3 shall not be applicable to enclosures. [NFPA 96:7.7.2.2.1 – 7.7.2.2.3]
Exception: Clearance from the outer surfaces of fieldapplied grease duct enclosures and factory-built grease duct enclosures to the interior surfaces of construction installed around them shall be permitted to be reduced where the field-applied grease duct enclosure materials and factory-built grease duct enclosures are installed in accordance with the conditions of the listing and the manufacturer’s instructions and are acceptable to the Authority Having Jurisdiction. [NFPA 96:7.7.2.2.4] 510.7.4 Mechanical and Structural Integrity. Fieldapplied grease duct enclosures and factory-built grease duct enclosures shall provide mechanical and structural
integrity, resiliency, and stability when subjected to expected building environmental conditions, duct movement under general operating conditions, and duct movement as a result of interior and exterior fire conditions.
[NFPA 96:7.7.2.2.5]
510.7.5 Materials. For field-applied grease duct enclosures and factory-built grease duct enclosures, the materials and products shall be provided in accordance with Section 510.7.5.1 and Section 510.7.5.2.
510.7.5.1 Protection from Physical Damage. Measures shall be taken to prevent physical damage to any covering or enclosure material. Any damage to the covering or enclosure shall be repaired, and the covering or enclosure shall be restored to meet its intended listing and fire resistance rating and to be acceptable to the Authority Having Jurisdiction.
[NFPA 96:7.7.3.1, 7.7.3.2]
CMC § 510.5.3 High relevance — show source text
510.5.3 Installation. All seams, joints, penetrations, and duct-to-hood collar connections shall have a liquidtight continuous external weld. [NFPA 96:7.5.2.1]
Exceptions:
(1) Factory-built grease ducts listed in accordance with UL 1978 shall be permitted to incorporate nonwelded joint construction in accordance with their listings. {NFPA 96:7.5.2.1.1}
(2) Duct-to-hood collar connections as shown in Figure 510.5.3 shall not require a liquidtight continuous external weld. [NFPA 96:7.5.2.2]
(3) Penetrations shall be permitted to be sealed by other listed devices that are tested to be greasetight and are evaluated under the same conditions of fire severity as the hood or enclosure of listed grease extractors and whose presence does not detract from the hood’s or duct’s structural integrity. [NFPA 96:7.5.2.3]
(4) Internal welding shall be permitted, provided the joint is formed or ground smooth and is readily accessible for inspection. [NFPA 96:7.5.2.4]
For SI units: 1 inch = 25.4 mm, °C = (°F-32)/1.8
FIGURE 510.5.3
PERMITTED DUCT-TO HOOD COLLAR CONNECTION
[NFPA 96: FIGURE 7.5.2.2]
510.5.3.1 Duct Leakage Test. Prior to the use of or concealment of any portion of a grease duct system, a leakage test shall be performed to determine that all welded joints and seams are liquid tight.
[NFPA 96:7.5.2.1.2]
510.5.3.2 Welded Duct Connection. Acceptable duct-to-duct connection shall be as follows:
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EXHAUST SYSTEMS
(1) Telescoping joint, as shown in Figure 510.5.3.2(1).
(2) Bell-type joint, as shown in Figure 510.5.3.2(2).
(3) Flange with edge weld, as shown in Figure 510.5.3.2(3).
(4) Flange with lap joint weld, as shown in Figure 510.5.3.2(4). [NFPA 96:7.5.5.1]
FIGURE 510.5.3.2(3)
FLANGE WITH EDGE WELD DUCT CONNECTION
[NFPA 96: FIGURE 7.5.5.1(c)]
For SI units: 1 inch = 25.4 mm
Notes:
1 Duct size decreases (going upward) with each telescope.
2 Smaller (inside) duct section shall be above or uphill (on sloped duct), to be self draining into larger (outside) duct.
FIGURE 510.5.3.2(1)
TELESCOPING -TYPE DUCT CONNECTION
[NFPA 96: FIGURE 7.5.5.1(a)]
For SI units: 1 inch = 25.4 mm
Notes:
1 Duct size stays the same throughout the duct system.
CMC § 507.4.3.3 High relevance — show source text
507.4.3.3 Protection Methods. The protection methods for ducts to reduce clearance shall be applied to the combustible or limited-combustible construction, not to the duct itself. [NFPA 96:4.2.4.4]
507.4.4 Factory Built. Factory-built grease duct enclosures shall be protected with a through-penetration firestop system classified in accordance with ASTM E814 or UL 1479 having an “F” and a “T” rating equal to the fire resistance rating of the assembly being penetrated from the point at which the duct penetrates a ceiling, wall, or floor to the outlet terminal. [NFPA 96:4.3.4]
507.4.4.1 Listing. The factory-built grease duct protection system shall be listed in accordance with UL 2221. [NFPA 96:4.3.4.1]
507.4.4.2 Single Wall. Listed single wall factorybuilt grease ducts shall be permitted to be enclosed with field-applied grease duct enclosure material where the material and the assembly of duct and material are listed for that application and installed in accordance with the grease duct manufacturer’s listing and their installation instructions. [NFPA 96:4.3.4.2]
507.4.4.3 Installation. The factory-built grease duct protection system shall be installed in accordance with the manufacturer’s instructions and the listing requirements. [NFPA 96:4.3.4.3]
507.4.5 Field Applied. Field-applied grease duct enclosures shall be protected with a through penetration firestop system classified in accordance with ASTM E814 or UL 1479 having an “F” and a “T” rating equal to the fire resistance rating of the assembly being penetrated. The surface of the field fabricated grease duct shall be continuously covered on all sides from the point at which the duct enclosure penetrates a ceiling, wall, or floor to the outlet terminal. The field-applied grease duct shall be listed in accordance with ASTM E2336 and installed in
accordance with the manufacturer’s instructions and the listing requirements. [NFPA 96:4.3.2 – 4.3.2.2]
507.4.6 Both Field-Applied and Factory Built. Field-applied grease duct enclosures and factory-built
grease duct enclosures shall demonstrate that they provide mechanical and structural integrity, resiliency, and stability when subjected to expected building environmental conditions, duct movement under general operating conditions, and duct movement due to fire conditions.
[NFPA 96:4.3.5]
507.4.6.1 Physical Damage. Measures shall be taken to prevent physical damage to a material or product used for the purpose of reducing clearances.
Exception: Where the duct is protected with a fieldapplied grease duct enclosure or factory-built grease duct enclosure.
507.4.6.2 Specification. The specifications of material, gauge, and construction of the duct used in the testing and listing of field-applied grease duct enclosures and factory-built grease duct enclosures shall be included as minimum requirements in their listing and installation documentation. [NFPA 96:4.3.6]
507.4.6.3 Clearance Options. The following clearance options for which field-applied grease duct enclosures and factory-built grease duct enclosures have been successfully evaluated shall be clearly identified in their listing and installation documentation and on their labels:
(1) Open combustible construction clearance at manufacturer’s requested dimensions.
CMC § 403.7.2 High relevance — show source text
ENCLOSED PARKING GARAGES . . . . . . . . . . . . . . 403.7.2
Alternative Exhaust Ventilation. . . . . . . . . . . . . 403.7.2.1
Exhaust Systems Operation. . . . . . . . . . . . . . . 403.7.2.4
Minimum Exhaust Rate . . . . . . . . . . . . . . . . . . 403.7.2.2
ENCLOSURE OF DUCTS,
COMMERCIAL KITCHEN EXHAUST
Clearances . . . . . . . . . . . . . . 507.4.6.3, 507.4.8, 510.7.3
Continuous. . . . . . . . . . . . . . . . . . . . . . . . . 205.0, 510.7
Ducts within . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510.7.8
Fire doors required . . . . . . . . . . . . . . . . . . . . . . . 510.7.7
Grease, factory built . . . . . . . . . . . . . . . . 208.0, 507.4.4,
507.4.6, 507.4.6.3
Grease duct, field-applied. . . . . . . . . . . . 208.0, 507.4.5,
507.4.6, 507.4.6.3
Product conveying ducts . . . . . . . . . . . . . . . . . . . . 505.8
ENCLOSURES
For equipment on roof. . . . . . . . . . . . . . . . . . . . . . 303.8
For boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1001.2
ENERGY STAR, DEFINITION . . . . . . . . . . . . . . . . . . E 201.1
ENFORCEMENT (SFM) . . . . . . . . . . . . . . . . . . . . . . . 1.11.2.1
ENFORCING AGENCY
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207.0
SFM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.11.2
ENGINE, GAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1602.0
EQUIPMENT
Clearances. . . . . . . . . 303.10, 303.10.1, Table 303.10.1
Converted equipment . . . . . . . . . . . . . . . . . . . . . . 902.3
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CMC § 519.5 High relevance — show source text
519.5, 701.11
Underground. . . . . . . . . . . . . . . . . . . . . . . 510.8, 603.11
– E –
ECONOMIZER, AIR . . . . . . . . . . . . . E 503.5.1, E 503.5.1.2,
Table E 503.5.1.2
ECONOMIZER, WATER . . . . . . . . . . E 503.5.2, E 503.5.2.1,
Table E 503.5.2
ECONOMIZERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407.6
ELECTRIC HEATING APPLIANCES
Air conditioners . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.1
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0
Duct heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 905.9
Room heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915.2
ELECTRICAL CODE
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207.0
ENCLOSED PARKING GARAGES . . . . . . . . . . . . . . 403.7.2
Alternative Exhaust Ventilation. . . . . . . . . . . . . 403.7.2.1
Exhaust Systems Operation. . . . . . . . . . . . . . . 403.7.2.4
Minimum Exhaust Rate . . . . . . . . . . . . . . . . . . 403.7.2.2
ENCLOSURE OF DUCTS,
COMMERCIAL KITCHEN EXHAUST
Clearances . . . . . . . . . . . . . . 507.4.6.3, 507.4.8, 510.7.3
Continuous. . . . . . . . . . . . . . . . . . . . . . . . . 205.0, 510.7
Ducts within . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510.7.8
Fire doors required . . . . . . . . . . . . . . . . . . . . . . . 510.7.7
Grease, factory built . . . . . . . . . . . . . . . . 208.0, 507.4.4,
507.4.6, 507.4.6.3
Grease duct, field-applied. . . . . . . . . . . . 208.0, 507.4.5,
507.4.6, 507.4.6.3
CMC § 510.3.7 Medium relevance — show source text
510.3.7 Fire Protection System Devices. Openings for installation, servicing, and inspection of listed fire protection system devices and for duct cleaning shall be provided in ducts and enclosures and shall be in accordance with the requirements of Section 510.3 through Section 510.3.2 and Section 510.7.7.
Enclosure openings required to reach access panels in the ductwork shall be large enough for removal of the access panel through the enclosure opening. [NFPA 96:7.4.4.1 – 7.4.4.2]
510.4 Listed Grease Ducts. Listed grease ducts shall be installed in accordance with the terms of the listing and the manufacturer’s instructions. [NFPA 96:7.1.8]
510.4.1 Factory-Built Grease Ducts. Factory-built grease ducts in accordance with UL 1978 shall be permitted to incorporate non-welded joints in accordance with their listings.
510.5 Other Grease Ducts. Other grease ducts shall comply with the requirements of Section 510.5.1 through Section 510.5.5. [NFPA 96:7.5]
510.5.1 Materials. Ducts shall be constructed of and
supported by carbon steel not less than 0.060 of an inch (1.524 mm) (No. 16 MSG) in thickness or stainless steel not less than 0.048 of an inch (1.219 mm) (No. 18 MSG) in thickness. [NFPA 96:7.5.1.1]
510.5.2 Factory-Built Grease Ducts. Factory-built grease ducts listed in accordance with UL 1978 shall be permitted to use materials in accordance with their listing. {NFPA 96:7.5.1.2}
510.5.3 Installation. All seams, joints, penetrations, and duct-to-hood collar connections shall have a liquidtight continuous external weld. [NFPA 96:7.5.2.1]
Exceptions:
(1) Factory-built grease ducts listed in accordance with UL 1978 shall be permitted to incorporate nonwelded joint construction in accordance with their listings. {NFPA 96:7.5.2.1.1}
(2) Duct-to-hood collar connections as shown in Figure 510.5.3 shall not require a liquidtight continuous external weld. [NFPA 96:7.5.2.2]
(3) Penetrations shall be permitted to be sealed by other listed devices that are tested to be greasetight and are evaluated under the same conditions of fire severity as the hood or enclosure of listed grease extractors and whose presence does not detract from the hood’s or duct’s structural integrity. [NFPA 96:7.5.2.3]
(4) Internal welding shall be permitted, provided the joint is formed or ground smooth and is readily accessible for inspection. [NFPA 96:7.5.2.4]
For SI units: 1 inch = 25.4 mm, °C = (°F-32)/1.8
FIGURE 510.5.3
PERMITTED DUCT-TO HOOD COLLAR CONNECTION
[NFPA 96: FIGURE 7.5.2.2]
CMC § 507.6 Medium relevance — show source text
507.6 Notification of Change . . . . . . . . . 111
507.7 Pharmaceutical Compounding Exhaust Discharge . . . . . . . . . . . . 111
508.0 Type I Hoods . . . . . . . . . . . . . . . . 111
508.1 Where Required . . . . . . . . . . . . . . 111
508.2 Listed Type I Hood Assemblies . . 111
508.3 Construction of Type I Hoods . . . . 111
508.4 Supports . . . . . . . . . . . . . . . . . . . . 112
508.5 Hood Size . . . . . . . . . . . . . . . . . . . 112
Table 508.5.1.2 Extra-Heavy-Duty Cooking Appliance Airflow . . . . . . . . . . . . . 113
Table 508.5.1.3 Heavy-Duty Cooking Appliance
Airflow. . . . . . . . . . . . . . . . . . . . . . 113
Table 508.5.1.4 Medium-Duty Cooking Appliance
Airflow. . . . . . . . . . . . . . . . . . . . . . 113
Table 508.5.1.5 Light-Duty Cooking Appliance
Airflow. . . . . . . . . . . . . . . . . . . . . . 113
508.6 Solid-Fuel Hood Assemblies . . . . 114
508.7 Exhaust Outlets . . . . . . . . . . . . . . 114
509.0 Grease Removal Devices in
Hoods . . . . . . . . . . . . . . . . . . . . . . 114
509.1 Grease Removal Devices. . . . . . . 114
509.2 Installation . . . . . . . . . . . . . . . . . . 114
509.3 Solid-Fuel Grease Removal
Devices. . . . . . . . . . . . . . . . . . . . . 115
510.0 Exhaust Duct Systems . . . . . . . . . 115
510.1 General. . . . . . . . . . . . . . . . . . . . . 115
510.2 Clearance . . . . . . . . . . . . . . . . . . . 115
510.3 Openings . . . . . . . . . . . . . . . . . . . 115
510.4 Listed Grease Ducts . . . . . . . . . . . 116
510.5 Other Grease Ducts . . . . . . . . . . . 116
510.6 Exterior Installations . . . . . . . . . . . 117
xxxii
510.7 Interior Installations . . . . . . . . . . . 118
510.8 Underground Installations. . . . . . . 118
510.9 Termination of Type I Hood Exhaust System . . . . . . . . . . . . . . 119
510.10 Solid-Fuel Duct Systems . . . . . . . 120
511.0 Air Movement . . . . . . . . . . . . . . . . 120
511.1 Exhaust Fans for Commercial
CMC § 508.2.4 Medium relevance — show source text
508.2.4 Assembly of Listed Exhaust Hoods. Listed exhaust hoods with or without exhaust dampers shall be permitted to be assembled in accordance with the listing requirements. [NFPA 96:5.1.7]
508.3 Construction of Type I Hoods. The hood or that portion of a primary collection means designed for collecting cooking vapors and residues shall be constructed of and be supported by steel not less than 0.048 of an inch (1.219 mm) (No. 18 MSG), in thickness, stainless steel not less than 0.036 of an inch (0.914 mm) (No. 20 MSG) in thickness, or other approved material of equivalent strength and fire and corrosion resistance. [NFPA 96:5.1.1]
Exception: Listed exhaust hoods.
508.3.1 Grease Vapor. Wall-mounted exhaust hood assemblies shall be tight fitting against the back wall so as to not permit passage of grease vapor behind the hood, or between the back wall and the hood assembly. [NFPA 96:5.1.13]
508.3.2 Seams, Joints, and Penetrations. All seams, joints, and penetrations of the hood enclosure that direct and capture grease-laden vapors and exhaust gases shall have a liquid-tight continuous external weld to the hood’s lower outermost perimeter. [NFPA 96:5.1.2]
Exceptions:
(1) Seams, joints, and penetrations of the hood shall be permitted to be internally welded, provided that the weld is formed smooth or ground smooth, so as to not trap grease, and is cleanable. [NFPA 96:5.1.3]
(2) Penetrations shall be permitted to be sealed by devices that are listed for such use and whose presence does not detract from the hood’s or duct’s structural integrity. [NFPA 96:5.1.5]
508.3.2.1 Sealed. Internal hood joints, seams, filter support frames, and appurtenances attached inside the hood shall be sealed or otherwise made greasetight. [NFPA 96:5.1.4]
508.3.3 Eyebrow-Type Hoods. Eyebrow-type hoods over gas or electric ovens shall be permitted to have a duct constructed as required in Section 510.0 from the oven flue(s) connected to the hood canopy upstream of the exhaust plenum, as shown in Figure 508.3.3. [NFPA 96:5.1.8.1]
2025 CALIFORNIA MECHANICAL CODE 111
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
EXHAUST SYSTEMS
FIGURE 508.3.3
TYPICAL SECTION OF EYEBROW-TYPE HOOD
[NFPA 96: FIGURE 5.1.8.1]
508.3.3.1 Duct Connection. The duct connect ing the oven flue(s) to the hood canopy shall be connected with a continuous weld or have a duct-to-duct
connection. [See Figure 511.1.2(2) through Figure 511.1.2(4)] [NFPA 96:5.1.8.2]
508.3.4 Insulation. Insulation materials other than
CMC § 603.2 Medium relevance — show source text
In under floor or crawl spaces. . . . . . . . . . . . . . . . 603.2
Inspection and cleaning of . . . . . . . . . . . 514.2, 514.4.2
Insulation of . . . . . . . . . . . . . . . . . . 605.0, 605.2, 605.3,
E 502.4.1, E 503.4.7.1,
Table E 503.7.2–Table E 503.7.3(2)
Joints and seams . . . . . . . . . . . . . . . . . . . . . . . . . 603.9
Leakage test . . . . . . . . . . . . . . . . . . . 603.9.2 , 603.9.2.1
Manifold (common duct) . . . . . . . . . . . . . . . . . . . . 511.4
Material of . . . . . . . . . . . . . . . . . . 506.1, 510.5.1, 602.0
Metal . . . . . . . . . . . . . . . . . 506.1, 602.5, 603.3, 603.7.1
Non-grease type. . . . . . . . . . . . . . . . . . . . . 519.4, 519.5
Nonmetallic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602.5
Openings. . . . . . . . . . . . . . . . 510.3, 510.3.3–510.3.3.2,
510.3.4.2, 511.1.5
Other grease . . . . . . . . . . . . . . . . . . . . . . 510.5, 602.5.4
Plastic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603.5
Product-conveying . . . . . . . . . . . . . . . . . 206.0, 502.2.2,
506.0, Table 506.2(1),
Table 506.2(2)
Protection of. . . . . . . . . . . . . . . . . . . . . . . . 506.9, 603.6
Return duct sizing . . . . . . . . . . . . . . . . . . . . . . . 601.2.1
Smoke Detectors . . . . . . . . . . . . . . . . . . . . . . . . 609.1.1
Solid-fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517.0
Support systems . . . . . . . . . . .504.4.5, 506.7–506.8.4,
510.1.6, 510.1.7, 510.3.3.3,
510.5.1, 603.3, 603.7
CMC § 206.0 Medium relevance — show source text
Environmental air. . . . . . . . . . . . . . . . . . . . 206.0, 504.0
Exhaust, commercial kitchen . . . . . . . . . . . . . . . . 510.0
Existing metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.2
Factory-made air. . . . . . . . . . . . . 603.4, 603.4.1, 603.7
Fire protection required . . . . . . . . . . . . . . . . . . . . . 506.8
Flexible air ducts and connectors. . . . . . . . . . . . . . 603.4,
603.4.1.1, 603.7.2
For kilns . . . . . . . . . . . . . . . . . 603.13.6, 930.5.3, 930.6
Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . 206.0, 905.0
Gravity ventilation . . . . . . . . . . . . . . . . . . . . . . . 930.5.3
Grease type . . . . . . . . . . . . . . . . . . . . . . . . 206.0, 510.0
Gypsum wallboard . . . . . . . . . . . . . . . . . . . . . . . 602.5.2
In under floor or crawl spaces. . . . . . . . . . . . . . . . 603.2
Inspection and cleaning of . . . . . . . . . . . 514.2, 514.4.2
Insulation of . . . . . . . . . . . . . . . . . . 605.0, 605.2, 605.3,
E 502.4.1, E 503.4.7.1,
Table E 503.7.2–Table E 503.7.3(2)
Joints and seams . . . . . . . . . . . . . . . . . . . . . . . . . 603.9
Leakage test . . . . . . . . . . . . . . . . . . . 603.9.2 , 603.9.2.1
Manifold (common duct) . . . . . . . . . . . . . . . . . . . . 511.4
Material of . . . . . . . . . . . . . . . . . . 506.1, 510.5.1, 602.0
Metal . . . . . . . . . . . . . . . . . 506.1, 602.5, 603.3, 603.7.1
Non-grease type. . . . . . . . . . . . . . . . . . . . . 519.4, 519.5
Nonmetallic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602.5
Frequently asked questions
Can a grease duct share a terminal with another exhaust (for example, building HVAC)?
No. Type I grease exhausts must be independent of other exhaust systems — sharing terminals or combining dissimilar exhausts into the same duct is not permitted under § 510.1.8.
If I enclose a grease duct in a continuous shaft, can I use the clearance‑reduction sheet protector to reduce clearances inside that shaft?
No. The clearance‑reduction methods of § 507.4 generally do not apply inside required continuous enclosures; you must follow the enclosure clearances in § 510.7.3 or use a listed enclosure/product that specifically allows a different clearance.
Where do I measure the required clearance from?
Measure from the outer surface of the grease duct to the nearest point on the combustible material unless a listing or enclosure specifies an alternate measurement method; this is the measurement method used in the clearance provisions referenced by § 510.2.
Can a listed factory‑built grease duct use non‑welded joints?
Yes — factory‑built grease ducts listed to the appropriate standard are permitted to use non‑welded joints in accordance with their listing. See § 510.4.1 and the installation exceptions in § 510.5.3.
If a duct passes within 6 inches of a noncombustible surface, is that okay?
For unenclosed ducts, contact with noncombustible materials is permitted (0 inches clearance) per § 507.4; but if the duct is inside a required enclosure, § 510.7.3 requires a minimum 6 inches clearance to the enclosure interior for noncombustible or limited‑combustible construction. Confirm the installation context.
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