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Chapter 5 — EXHAUST SYSTEMS

511.2 Airflow. The air velocity through a duct shall be not

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.

less than 500 feet per minute (ft/min) (2.54 m/s) and not exceed 2500 ft/min (12.7 m/s).

(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 a size to allow

for service or removal. [NFPA 96:8.1.4.2]

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 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 approved by 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.

(1) Located in an accessible area of a size to allow

for service or removal. [NFPA 96:8.1.4.2] (2) Flexible connectors shall be prohibited. [NFPA

96:8.1.4.5]

(2) Flexible connectors shall be prohibited. [NFPA

96:8.1.4.5] (3) A drain shall be directed to a readily accessible

and visible grease receptacle not to exceed 1

(3) A drain shall be directed to a readily accessible

and visible grease receptacle not to exceed 1 gallon (4 L). [NFPA 96:8.1.4.6] 511.1.3.3 Duct Systems. Duct systems connected to fans in an enclosure shall be in accordance with the following: (1) The space or room in which the exhaust fan is

located shall have the same fire resistance rating

(1) The space or room in which the exhaust fan is

located shall have the same fire resistance rating as the enclosure. (2) The fan shall be connected to the exhaust duct

by flanges securely bolted as shown in Figure

511.2.2.1 Performance Test. A performance test shall be conducted upon completion and before final approval of the installation of a ventilation system serving commercial cooking appliances. The test shall verify the rate of exhaust airflow in accordance with Section 508.5.1.2 through Section 508.5.1.5. The permit holder shall furnish the necessary test equipment and devices required to perform the tests.

Performance Test.** A performance test shall be conducted upon completion and before final approval of the installation of a ventilation system serving commercial cooking appliances. The test shall verify the rate of exhaust airflow in accordance with Section 508.5.1.2 through Section 508.5.1.5. The permit holder shall furnish the necessary test equipment and devices required to perform the tests.

[ASHRAE 154:4.7.1] 511.2.2.2 Capture and Containment Test. The permit holder shall verify the capture and containment performance of Type I hoods. A field test shall be conducted with all appliances under the hood at operating temperatures, all the hoods operating at design airflows, and with all sources of replacement air operating at design airflows for the restaurant. Capture and containment shall be verified visually by observing smoke or steam produced by actual cooking operation or by simulating cooking using devices such as smoke candles or smoke puffers. Smoke bombs shall not be used. [ASHRAE 154:4.7.2] 511.2.3 Operation. A hood exhaust fan(s) shall continue to operate after the extinguishing system has been activated, unless fan shutdown is required by a listed component of the ventilation system, or by the design of the extinguishing system. The hood exhaust fan shall not be required to start upon activation of the extinguishing system where the exhaust fan and cooking equipment served by the fan have been shut down. The exhaust fan shall be provided with a means so that the fan is activated when an appliance under the hood is turned on. [NFPA 96:8.2.3]

(2) 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, 8.1.4.4] 511.1.4 Construction. Exhaust fan housings shall be constructed of carbon steel not less than 0.060 of an 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, where listed, in accordance with the terms of the listing. [NFPA 96:8.1.5]

106 2019 CALIFORNIA MECHANICAL CODE

EXHAUST SYSTEM

FIGURE 511.1.2(1) TYPICAL SECTION OF DUCT-TO-FAN CONNECTION-BUTT JOINT METHOD

[NFPA 96: FIGURE 8.1.3.2(a)]

FIGURE 511.1.2(2) TYPICAL SECTION OF DUCT-TO-FAN CONNECTION-OVERLAPPING METHOD

[NFPA 96: FIGURE 8.1.3.2(b)]

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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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