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Chapter 5 — EXHAUST SYSTEMS

510.1 General. Ducts shall not pass through fire walls.

California Mechanical Code (Title 24, Part 4) · 2022 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]

510.1.1 Fire Hazards. All ducts shall lead directly to the exterior of the building, so as not to unduly increase any fire hazard. [NFPA 96:7.1.2] 510.1.2 Interconnection. Duct systems shall not be interconnected with any other building ventilation or exhaust system. [NFPA 96:7.1.3] 510.1.3 Duct Installation. All ducts shall be installed with a minimum 2 percent slope on horizontal runs up to 75 feet (22 860 mm) and a minimum 8 percent slope on horizontal runs greater than 75 feet (22 860 mm). Fac

tory-built grease ducts shall be permitted to be installed at a lesser slope in accordance with the listing and the manufacturer’s instructions. All 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 in accordance with the terms of the listing and the manufacturer’s installation manual.

All 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 comply with Section 510.3 through Section 510.3.2. [NFPA 96:7.1.5] 510.1.5 Sign. A sign stating the following shall be placed on all access panels: 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 listing and the manufacturer’s 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. This chapter includes requirements for
    2. 502.1 Exhaust Opening Protection. Exhaust openings
    3. 502.2 Termination of Exhaust Ducts. Exhaust ducts
    4. 503.1 General. Motors and fans shall be sized to provide
    5. 503.2 Fans. Parts of fans in contact with explosive or flammab…
    6. 504.1 General. Where not specified in this chapter, exhaust
    7. 504.2 Independent Exhaust Systems. Single or combined mechanic…
    8. 504.3 Domestic Range. Ducts used for domestic kitchen
    9. 504.4 Clothes Dryers. A clothes dryer exhaust duct shall not
    10. 504.5 Heat (Energy) Recovery Ventilators. Heat
    11. 504.6 Gypsum Wallboard Ducts. Bathroom and laundry
    12. 505.1 General. A mechanical ventilation or exhaust system
    13. 505.2 Incompatible Materials. Incompatible materials
    14. 505.3 Flammability Limit. Unless the circumstances stipulated …
    15. 505.4 Air-Moving Devices. Air-moving devices shall be
    16. 505.5 Generating Flames, Sparks, or Hot Materials.
    17. 505.6 Fire Dampers. Fire dampers shall be permitted to be
    18. 505.7 Fire Detection and Alarm Systems. Unless the
    19. 505.8 Product-Conveying Ducts Classification. Product-conveyin…
    20. 505.9 Minimum Velocities and Circulation. The velocity and cir…
    21. 505.10 Makeup Air. Makeup air shall be provided to replenish a…
    22. 505.11 Hoods and Enclosures. Hoods and enclosures shall
    23. 505.12 Pharmacies – Compounding Area of Par-
    24. 506.1 Materials. Materials used in product-conveying duct
    25. 506.2 Construction. Ducts used for conveying products
    26. 506.3 Penetrations. Exhaust ducts shall not pass through
    27. 506.4 Condensate. Joints in duct construction shall be liquidt…
    28. 506.5 Fittings. Fittings in Class 2, 3, and 4 systems shall be
    29. 506.6 Explosion Venting. Ducts conveying explosive dusts
    30. 506.7 Supports. Supports shall be of noncombustible materials,…
    31. 506.8 Fire Protection. Sprinklers or other fire-protection
    32. 506.9 Protection from Physical Damage. Ducts
    33. 506.10 Duct Clearances. Unless the conditions stipulated
    34. 506.11 Clearance Reduction Methods. It shall be permitted to p…
    35. 507.1 Type I Hood Exhaust System. Exhaust systems
    36. 507.2 Exhaust System. Cooking equipment used in
    37. 507.3 Listed Devices. Penetrations shall be sealed with
    38. 507.4 Clearance. Where enclosures are not required, hoods,
    39. 507.5 Drawings. A drawing(s) of the exhaust system installatio…
    40. 507.6 Notification of Change. If required by the Authority Hav…
    41. 507.7 Pharmaceutical Compounding Exhaust Dis-
    42. 508.1 Where Required. Type I hoods shall be installed at
    43. 508.2 Listed Type I Hood Assemblies. Listed hood
    44. 508.3 Construction of Type I Hoods. The hood or that
    45. 508.4 Supports. Hoods shall be secured in place [OSHPD
    46. 508.5 Hood Size. Hoods shall be sized in accordance with
    47. 508.6 Solid-Fuel Hood Assemblies. Where solid-fuel
    48. 508.7 Exhaust Outlets. An exhaust outlet within an
    49. 509.1 Grease Removal Devices. Listed grease filters or
    50. 509.2 Installation. The distance between the grease removal
    51. 509.3 Solid-Fuel Grease Removal Devices. Where
    52. 510.1 General. Ducts shall not pass through fire walls.
    53. 510.2 Clearance. Clearance between ducts and combustible
    54. 510.3 Openings. Openings shall be provided at the sides or
    55. 510.4 Listed Grease Ducts. Listed grease ducts shall be
    56. 510.5 Other Grease Ducts. Other grease ducts shall comply with…
    57. 510.6 Exterior Installations. The exterior portion of the
    58. 510.7 Interior Installations. In all buildings more than one
    59. 510.8 Underground Installations. Grease ducts installed
    60. 510.9 Termination of Type I Hood Exhaust System.
    61. 510.10 Solid-Fuel Duct Systems. Where solid-fuel cooking equip…
    62. 511.1 Exhaust Fans for Commercial Cooking Opera-
    63. 511.2 Airflow. The air velocity through a duct shall be not
    64. 511.3 Makeup Air. The makeup air quantity shall prevent
    65. 511.4 Common Duct (Manifold) Systems. Master
    66. 511.5 Solid-Fuel Air Movement Requirements. Where
    67. 512.1 Dampers. Dampers shall not be installed in exhaust
    68. 512.2 Electrical Equipment. Wiring systems of any type
    69. 512.3 Other Equipment. Fume incinerators, thermal recovery uni…
    70. 512.4 Solid-Fuel Auxiliary Equipment. Where solid fuel
    71. 513.1 General. Fire-extinguishing equipment for the protection…
    72. 513.2 Types of Equipment. Fire-extinguishing equipment
    73. 513.3 Simultaneous Operation. Fixed pipe extinguishing
    74. 513.4 Fuel and Electric Power Shutoff. Upon activation of
    75. 513.5 Manual Activation. All systems shall have both automatic…
    76. 514.2 Inspection, Testing, and Maintenance. Maintenance of the…
    77. 513.6 System Annunciation. Upon activation of an automatic fir…
    78. 513.7 Special Design and Application. Hoods containing
    79. 513.8 Review and Certification. Where required, complete
    80. 513.9 Installation Requirements. Installation of systems
    81. 513.10 Portable Fire Extinguishers. Portable fire extinguisher…
    82. 513.11 Maintenance. Portable fire extinguishers shall be
    83. 513.12 Solid-Fuel Fire-Extinguishing Equipment.
    84. 514.1 Operating Procedures. Exhaust systems shall be
    85. 514.3 Inspection for Grease Buildup. The entire exhaust
    86. 514.4 Cleaning of Exhaust Systems. If, upon inspection,
    87. 514.5 Cooking Equipment Maintenance. Inspection and
    88. 515.1 Cooking Equipment. Cooking equipment shall be
    89. 515.2 Operating Controls. Deep-fat fryers shall be equipped
    90. 516.1 General Requirements. Recirculating systems containing o…
    91. 516.2 Design Restrictions. All recirculating systems shall
    92. 516.3 Interlocks. The recirculating system shall be provided
    93. 516.4 Location and Application Restrictions. The
    94. 516.5 Additional Fire Safety Requirements. In addition to the …
    95. 516.6 Use and Maintenance. Automatic or manual covers on cooki…
    96. 517.1 Venting Application. Venting requirements of solidfuel c…
    97. 517.2 Location of Appliances. Every appliance shall be
    98. 517.3 Hoods for Solid-Fuel Cooking. Hoods shall be sized
    99. 517.4 Exhaust Systems for Solid-Fuel Cooking. Where
    100. 517.5 Grease Removal Devices for Solid-Fuel Cook-
    101. 517.6 Air Movement for Solid-Fuel Cooking. Exhaust
    102. 517.7 Fire-Extinguishing Equipment for Solid-Fuel
    103. 517.8 Other Safety Requirements. Metal-fabricated solidfuel co…
    104. 518.1 General. Downdraft appliance ventilation system
    105. 518.2 Ventilation System. The downdraft appliance ventilation …
    106. 518.3 Fire-Extinguishing Equipment. For fire-extinguishing equ…
    107. 518.4 Airflow Switch or Transducer. An airflow switch or
    108. 518.5 Surface Materials. Any surface located directly
    109. 519.1 Where Required. Type II hoods shall be installed
    110. 519.2 Construction of Type II Hoods. Type II hoods
    111. 519.3 Dishwashing Appliances. The net airflow for Type
    112. 519.4 Type II Exhaust Duct Systems. Ducts and
    113. 519.5 Termination of Type II Hood Exhaust System.
    114. 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 — GEOTHERMAL ENERGY SYSTEMS
  24. Appendix G — SIZING OF VENTING SYSTEMS AND OUTDOOR COMBUSTION …
  25. Appendix H — EXAMPLE CALCULATION OF OUTDOOR AIR RATE

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