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Chapter 5 — EXHAUST SYSTEMS

504.4 Clothes Dryers. A clothes dryer exhaust duct shall

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.

not be connected to a vent connector, gas vent, chimney, and shall not terminate into a crawl space, attic, or other concealed space. Exhaust ducts shall not be assembled with screws or other fastening means that extend into the duct and that are capable of catching lint, and that reduce the efficiency of the exhaust system. Exhaust ducts shall be constructed of rigid metallic material. Transition ducts used to connect the dryer to the exhaust duct shall be listed and labeled in accordance with UL 2158A, or installed in accordance with the clothes dryer manufacturer’s installation instructions. Clothes dryer exhaust ducts shall terminate to the outside of the building in accordance with Section 502.2.1 and shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination. Devices, such as fire or smoke dampers that will obstruct the flow of the exhaust shall not be used. Where joining of ducts, the male end shall be inserted in the direction of airflow.

504.4.1 Provisions for Makeup Air. Makeup air shall be provided in accordance with the following: (1) Makeup air shall be provided for Type 1 clothes dry ers in accordance with the manufacturer’s instruc

504.4.2.1 Length Limitation. Unless otherwise permitted or required by the dryer manufacturer’s instructions and approved by the Authority Having Jurisdiction, domestic dryer moisture exhaust ducts shall not exceed a total combined horizontal and vertical length of 14 feet (4267 mm), including two 90 degree (1.57 rad) elbows. A length of 2 feet (610 mm) shall be deducted for each 90 degree (1.57 rad) elbow in excess of two. Exception: Where an exhaust duct power ventilator, in accordance with Section 504.4.2.3, is used, the maximum length of the dryer exhaust duct shall be permitted to be in accordance with the dryer exhaust duct power ventilator manufacturer’s installation instructions. 504.4.2.2 Transition Ducts. Listed clothes dryer transition ducts not more than 6 feet (1829 mm) in length shall be permitted to be used to connect the Type 1 dryer to the exhaust ducts. Transition ducts and flexible clothes dryer transition ducts shall not be concealed within construction, and shall be installed in accordance with the manufacturer’s installation instructions. 504.4.2.3 Exhaust Duct Power Ventilators. Dryer exhaust duct power ventilators for single residential clothes dryers shall be listed and labeled in accordance with UL 705 and installed in accordance with the manufacturer’s installation instructions. 504.4.3 Commercial Clothes Dryers. Commercial dryer exhaust ducts shall be installed in accordance with their listings. The installation of commercial clothes dryer exhaust ducts shall comply with the appliance manufacturer’s installation instructions.

hes dryers shall be listed and labeled in accordance with UL 705 and installed in accordance with the manufacturer’s installation instructions. 504.4.3 Commercial Clothes Dryers. Commercial dryer exhaust ducts shall be installed in accordance with their listings. The installation of commercial clothes dryer exhaust ducts shall comply with the appliance manufacturer’s installation instructions.

(1) Makeup air shall be provided for Type 1 clothes dry ers in accordance with the manufacturer’s instructions. [NFPA 54:10.4.3.1] Where a closet is designed for the installation of a clothes dryer, an opening of not less than 100 square inches (0.065 m 2 ) for makeup air shall be provided in the door or by other approved means. (2) Provision for makeup air shall be provided for Type

2 clothes dryers, with a free area of not less than 1

Dryers.504.4.3.1 Exhaust Ducts for Type 2 Clothes Exhaust ducts for Type 2 clothes dryers shall comply with the following: (1) Exhaust ducts for Type 2 clothes dryers shall

comply with Section 504.4. [NFPA 54:10.4.5.1]

(1) Exhaust ducts for Type 2 clothes dryers shall

comply with Section 504.4. [NFPA 54:10.4.5.1] (2) Exhaust ducts for Type 2 clothes dryers shall be

constructed of sheet metal or other noncom

(2) Provision for makeup air shall be provided for Type

2 clothes dryers, with a free area of not less than 1 square inch (0.0006 m 2 ) for each 1000 British thermal units per hour (Btu/h) (0.293 kW) total input rating of the dryer(s) installed. [NFPA 54:10.4.3.2] 504.4.2 Domestic Clothes Dryers. Where a compartment or space for a Type 1 clothes dryer is provided, not less than a 4 inch diameter (102 mm) exhaust duct of approved material shall be installed in accordance with Section 504.0.

(2) Exhaust ducts for Type 2 clothes dryers shall be

constructed of sheet metal or other noncombustible material. Such ducts shall be equivalent in strength and corrosion resistance to ducts made of galvanized sheet steel not less than 0.0195 of an inch (0.4953 mm) thick. [NFPA 54:10.4.5.2] (3) Type 2 clothes dryers shall be equipped or

installed with lint-controlling means. [NFPA

Exhaust ducts for Type 2 clothes dryers shall be

installed with a clearance of not less than 6 inches (152 mm) from adjacent combustible

(3) Type 2 clothes dryers shall be equipped or

installed with lint-controlling means. [NFPA 54:10.4.5.3] (4) Exhaust ducts for Type 2 clothes dryers shall be

installed with a clearance of not less than 6

86 2019 CALIFORNIA MECHANICAL CODE

EXHAUST SYSTEM

material. Where exhaust ducts for Type 2 clothes dryers are installed with reduced clearances, the adjacent combustible material shall be protected in accordance with Table 303.10.1.

[NFPA 54:10.4.5.4] (5) Where ducts pass through walls, floors, or par titions, the space around the duct shall be

(5) Where ducts pass through walls, floors, or par titions, the space around the duct shall be sealed with noncombustible material. [NFPA 54:10.4.5.5] (6) Multiple installations of Type 2 clothes dryers

shall be made in a manner to prevent adverse

to a safe location or treated by removing contaminants. Ducts conveying explosives or flammable vapors, fumes, or dusts shall extend directly to the exterior of the building without entering other spaces and shall not extend into or through ducts and plenums. Exception: Ducts conveying vapor or fumes having flammable constituents less than 25 percent of their Lower Flammability Limit (LFL) shall be permitted to pass through other spaces.

505.1.1 Mechanical Ventilation. A mechanical ventilation system shall be interlocked to operate with the equipment used to produce vapors, fumes, or dusts that are flammable or hazardous.

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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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