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Chapter 5 — EXHAUST SYSTEMS

510.0 Exhaust Duct Systems.510.1 General. Ducts shall not pass through fire walls.

California Mechanical Code (Title 24, Part 4) · 2019 edition · updated 2026-09-10 · California

Italicized text is a California amendment to the model code, as printed in the official publication.

[NFPA 96:7.1.1]

509.2.2.1 Installation. This protection shall be permitted to be accomplished by the installation of a steel or stainless steel baffle plate between the heat source and the grease removal device. [NFPA 96:6.2.2.2] 509.2.2.2 Size and Location. The baffle plate shall be sized and located so that flames or combustion gases shall travel a distance not less than 18 inches (457 mm) from the heat source to the grease removal device. [NFPA 96:6.2.2.3] 509.2.2.3 Clearance. The baffle shall be located not less than 6 inches (152 mm) from the grease removal devices. [NFPA 96:6.2.2.4] 509.2.3 Grease Filters. Grease filters shall be listed and constructed of steel or other non-combustible material, and shall be of rigid construction that will not distort or crush under normal operation, handling, cleaning, or replacement. [SFM] For applications listed in Section 1.11.0 regulated by the Office of the State Fire Marshal, grease filters shall be Class I when tested in accordance with the test method in Title 24, Part 12, Chapter 12-71, SFM Standard 12-71-1.

510.1.1 Fire Hazards. Ducts shall lead as directly to the exterior of the building, so as not to unduly increase a fire hazard. [NFPA 96:7.1.2] 510.1.2 Interconnection. Duct systems shall not be interconnected with a building ventilation or exhaust system. [NFPA 96:7.1.3] 510.1.3 Duct Installation. Ducts shall be installed with not less than 2 percent slope on horizontal runs up to 75 feet (22 860 mm) and not less than 8 percent slope on horizontal runs more than 75 feet (22 860 mm). Factorybuilt grease ducts shall be permitted to be installed in accordance with the listing and the manufacturer’s installation instructions. Horizontal ducts shall be provided with access in accordance with Section 510.3.3.

Drains shall be provided at low points in horizontal ducts. Where provided, drains shall be continuously welded to the exhaust duct or listed grease duct drains in accordance with the terms of the listing and the manufacturer’s installation instructions.

509.2.3.1 Arrangement. Grease filters shall be arranged so that exhaust air passes through the grease filters. [NFPA 96:6.2.3.4] 509.2.3.2 Accessibility. Grease filters shall be easily accessible for removal. [NFPA 96:6.2.3.5] 509.2.3.3 Angled Installation. Grease filters shall be installed at an angle not less than 45 degrees (0.79 rad) from the horizontal. [NFPA 96:6.2.3.6] 509.2.3.4 [DPH] Grease filters shall be Class I when tested in accordance with the test method in SFM 12-71-1. 509.2.4 Grease Drip Trays. Grease filters shall be equipped with a grease drip tray beneath their lower edges. [NFPA 96:6.2.4.1]

509.2.4.1 Size and Pitch. Grease drip trays shall be kept to the minimum size needed to collect grease and shall be pitched to drain into an enclosed metal container having a capacity not exceeding 1 gallon (4 L). [NFPA 96:6.2.4.2, 6.2.4.3]

Ducts shall be installed without forming dips or traps. In manifold (common duct) systems, the lowest end of the main duct shall be connected flush on the bottom with the branch duct. [NFPA 96:7.1.4 – 7.1.4.5] 510.1.4 Accessibility. Openings required for accessibility shall be in accordance with Section 510.3 through Section 510.3.2. [NFPA 96:7.1.5] 510.1.5 Sign. A sign shall be placed on access panels stating the following: ACCESS PANEL – DO NOT OBSTRUCT [NFPA 96:7.1.6] 510.1.6 Bracing and Supports. Duct bracing and supports shall be of noncombustible material, securely attached to the structure and designed to carry gravity and lateral loads within the stress limitations of the building code. Bolts, screws, rivets, and other mechanical fasteners shall not penetrate duct walls. 510.1.7 Type I Exhaust Duct Systems. Listed grease ducts shall be installed in accordance with the terms of their listings and manufacturer’s installation instructions.

[NFPA 96:7.1.7]

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▸Contents — California Mechanical Code (Title 24, Part 4)
California Mechanical Code (Title 24, Part 4)
  1. Chapter 1 — GENERAL CODE PROVISIONS
  2. Chapter 2 — DEFINITIONS
  3. Chapter 3 — GENERAL REGULATIONS
  4. Chapter 4 — VENTILATION AIR
  5. ▸Chapter 5 — EXHAUST SYSTEMS
    Overview
    1. 501.1 Applicability.501.0 General. This chapter includes requi…
    2. 502.2 Termination of Exhaust Ducts. Exhaust ducts shall
    3. 503.0 Motors, Fans, and Filters.503.1 General. Motors and fans…
    4. 503.2 Fans. Parts of fans in contact with explosive or flammab…
    5. 504.0 Environmental Air Ducts.504.1 General. Where not specifi…
    6. 504.2 Independent Exhaust Systems. Single or combined mechanic…
    7. 504.3 Domestic Range. Ducts used for domestic kitchen
    8. 504.4 Clothes Dryers. A clothes dryer exhaust duct shall
    9. 505.2 Incompatible Materials. Incompatible materials
    10. 505.3 Flammability Limit. Unless the circumstances stipulated …
    11. 504.5 Heat (Energy) Recovery Ventilators. Heat
    12. 504.6 Gypsum Wallboard Ducts. Bathroom and laundry
    13. 505.1 General.505.0 Product-Conveying Systems. A mechanical ve…
    14. 505.4 Air-Moving Devices. Air-moving devices shall be
    15. 505.5 Generating Flames, Sparks, or Hot Materials. Operations …
    16. 505.6 Fire Dampers. Fire dampers shall be permitted to be
    17. 505.8 Product-Conveying Ducts Classification. Product-conveyin…
    18. 505.7 Fire Detection and Alarm Systems. Unless the
    19. 505.9 Minimum Velocities and Circulation. The velocity and cir…
    20. 505.10 Makeup Air. Makeup air shall be provided to replenish a…
    21. 505.11 Hoods and Enclosures. Hoods and enclosures shall
    22. 506.2 Construction. Ducts used for conveying products
    23. 506.0 Product-Conveying Ducts.506.1 Materials. Materials used …
    24. 506.3 Penetrations. Exhaust ducts shall not pass through
    25. 506.5 Fittings. Fittings in Class 2, 3, and 4 systems shall be
    26. 506.4 Condensate. Joints in duct construction shall be liquidt…
    27. 506.6 Explosion Venting. Ducts conveying explosive dusts
    28. 506.9 Protection from Physical Damage. Ducts
    29. 506.7 Supports. Supports shall be of noncombustible materials,…
    30. 506.8 Fire Protection. Sprinklers or other fire-protection
    31. 506.11 Clearance Reduction Methods. It shall be permitted to p…
    32. 506.10 Duct Clearances. Unless the conditions in Section
    33. 507.4 Clearance. Where enclosures are not required, hoods,
    34. 507.1 Type I Hood Exhaust System.507.0 General Requirements. E…
    35. 507.2 Exhaust System. Cooking equipment used in
    36. 507.3 Listed Devices. Penetrations shall be sealed with
    37. 507.5 Drawings. A drawing(s) of the exhaust system installatio…
    38. 507.6 Notification of Change. Where required by the
    39. 508.1 Where Required.508.0 Type I Hoods. Type I hoods shall be…
    40. 508.2 Listed Type I Hood Assemblies. Listed hood
    41. 508.3 Construction of Type I Hoods. The hood or that
    42. 508.4 Supports. Hoods shall be secured in place [OSHPD 1,
    43. 508.5 Hood Size. Hoods shall be sized in accordance with
    44. 508.6 Solid-Fuel Hood Assemblies. Where solid-fuel
    45. 508.7 Exhaust Outlets. An exhaust outlet within an
    46. 509.0 Grease Removal Devices in Hoods.509.1 Grease Removal Dev…
    47. 509.2 Installation. The distance between the grease
    48. 509.3 Solid-Fuel Grease Removal Devices. Where
    49. 510.0 Exhaust Duct Systems.510.1 General. Ducts shall not pass…
    50. 510.2 Clearance. Clearance between ducts and combustible
    51. 510.3 Openings. Openings shall be provided at the sides
    52. 510.4 Listed Grease Ducts. Listed grease ducts shall be
    53. 510.5 Other Grease Ducts. Other grease ducts shall comply with…
    54. 510.6 Exterior Installations. The exterior portion of the
    55. 510.7 Interior Installations. In buildings more than one
    56. 510.8 Underground Installations. Grease ducts installed
    57. 511.0 Air Movement.
    58. 510.10 Solid-Fuel Duct Systems. Where solid-fuel cooking equip…
    59. 511.2 Airflow. The air velocity through a duct shall be not
    60. 511.3 Makeup Air. The makeup air quantity shall prevent
    61. 511.4 Common Duct (Manifold) Systems. Master
    62. 511.5 Solid-Fuel Air Movement Requirements. Where
    63. 512.1 Dampers.512.0 Auxiliary Equipment. Dampers shall not be …
    64. 512.2 Electrical Equipment. Wiring systems shall not be
    65. 512.3 Other Equipment. Fume incinerators, thermal recovery uni…
    66. 512.4 Solid-Fuel Auxiliary Equipment. Where solid fuel
    67. 513.2 Types of Equipment. Fire-extinguishing equipment
    68. 513.6 System Annunciation. Upon activation of an automatic fir…
    69. 513.3 Simultaneous Operation. Fixed pipe extinguishing systems…
    70. 513.4 Fuel and Electric Power Shutoff. Upon activation
    71. 513.5 Manual Activation. A readily accessible means for
    72. 513.7 System Supervision. Where electrical power is
    73. 513.8 Special Design and Application. Hoods containing automat…
    74. 513.9 Review and Certification. Where required, complete
    75. 513.10 Installation Requirements. Installation of systems
    76. 513.11 Portable Fire Extinguishers. Portable fire extinguisher…
    77. 513.12 Maintenance. Portable fire extinguishers shall be
    78. 513.13 Solid-Fuel Fire-Extinguishing Equipment. Where
    79. 514.0 Procedures for the Use, Inspection, Testing, and
    80. 514.2 Inspection, Testing, and Maintenance. Maintenance of the…
    81. 514.3 Inspection for Grease Buildup. The entire exhaust
    82. 514.4 Cleaning of Exhaust Systems. Where, upon
    83. 514.5 Cooking Equipment Maintenance. Inspection and
    84. 515.1 Cooking Equipment.Equipment. Cooking equipment shall be
    85. 515.2 Operating Controls. Deep-fat fryers shall be equipped
    86. 516.1 General Requirements.516.0 Recirculating Systems. Recirc…
    87. 516.2 Design Restrictions. Recirculating systems shall
    88. 516.6 Use and Maintenance. Automatic or manual covers
    89. 517.1 Venting Application.517.0 Solid-Fuel Cooking Operations.…
    90. 516.3 Interlocks. The recirculating system shall be provided w…
    91. 516.4 Location and Application Restrictions. The
    92. 516.5 Additional Fire Safety Requirements. In addition to the …
    93. 517.2 Location of Appliances. Appliances shall be
    94. 517.3 Hoods for Solid-Fuel Cooking. Hoods shall be
    95. 517.4 Exhaust Systems for Solid-Fuel Cooking. Where
    96. 517.6 Air Movement for Solid-Fuel Cooking. Exhaust
    97. 517.7 Fire-Extinguishing Equipment for Solid-FuelCooking. Soli…
    98. 517.8 Other Safety Requirements. Metal-fabricated solidfuel co…
    99. 518.4 Airflow Switch or Transducer. An airflow switch or
    100. 518.5 Surface Materials. Surfaces located directly above
    101. 518.0 Downdraft Appliances.518.1 General. A downdraft applianc…
    102. 518.2 Ventilation System. The downdraft appliance ventilation …
    103. 518.3 Fire-Extinguishing Equipment. Fire-extinguishing
    104. 519.0 Type II Hood Exhaust System Requirements.519.1 Where Req…
    105. 519.2 Construction of Type II Hoods. Type II hoods constructed…
    106. 519.3 Dishwashing Appliances. The net airflow for Type
    107. 519.4 Type II Exhaust Duct Systems. Ducts and plenums
    108. 519.5 Termination of Type II Hood Exhaust System.
    109. 519.6 Makeup Air. Makeup air shall be provided in accordance w…
  6. Chapter 6 — DUCT SYSTEMS
  7. Chapter 7 — COMBUSTION AIR
  8. Chapter 8 — CHIMNEYS AND VENTS
  9. Chapter 9 — INSTALLATION OF SPECIFIC APPLIANCES
  10. Chapter 10 — BOILERS AND PRESSURE VESSELS
  11. Chapter 11 — REFRIGERATION
  12. Chapter 12 — HYDRONICS
  13. Chapter 13 — FUEL GAS PIPING
  14. Chapter 14 — PROCESS PIPING
  15. Chapter 15 — SOLAR ENERGY SYSTEMS
  16. Chapter 16 — STATIONARY POWER PLANTS
  17. Chapter 17 — REFERENCED STANDARDS
  18. Appendix A — RESIDENTIAL PLAN EXAMINER REVIEW FORM FOR HVAC SY…
  19. Appendix B — PROCEDURES TO BE FOLLOWED TO PLACE GAS EQUIPMENT …
  20. Appendix C — INSTALLATION AND TESTING OF OIL (LIQUID) FUEL-FIR…
  21. Appendix D — FUEL SUPPLY: MANUFACTURED/MOBILE HOME PARKS AND R…
  22. Appendix E — SUSTAINABLE PRACTICES
  23. Appendix F — SIZING OF VENTING SYSTEMS AND OUTDOOR COMBUSTION …
  24. Appendix G — EXAMPLE CALCULATION OF OUTDOOR AIR RATE

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