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Chapter 3 — GENERAL REGULATIONS

305.4 Drainage Pan. Where a water heater is located in an

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.

attic, in or on an attic ceiling assembly, floor-ceiling assembly, or floor-subfloor assembly where damage results from a leaking water heater, a watertight pan of corrosion-resistant materials shall be installed beneath the water heater with not less than 3 ⁄4 of an inch (20 mm) diameter drain to an approved location. Such pan shall be not less than 1 1 ⁄2 inches (38 mm) in depth.

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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
    Overview
    1. 301.2 Approval. Equipment or appliance shall be approved
    2. 301.3 Design of Equipment. Installers shall furnish satisfacto…
    3. 301.4 Electrical Connections. For equipment regulated
    4. 301.5 Oil-Burning Appliances. The tank, piping, and
    5. 301.6 Personnel Protection. A metal guard shall be provided ar…
    6. 302.0 Materials – Standards and Alternates.302.1 Minimum Stand…
    7. 302.2 Alternate Materials and Methods of Construc-tion Equival…
    8. 302.3 Alternative Engineered Design. An alternative
    9. 303.2 Closet or Alcove Installations. Central heating
    10. 303.3 Unlisted Appliances. Except as otherwise permitted in th…
    11. 303.4 Anchorage of Appliances. Appliances designed to
    12. 303.5 Movement. Movement of appliances with casters
    13. 303.6 Identification of Equipment. Where more than one
    14. 303.7 Liquefied Petroleum Gas Facilities. Containers,
    15. 303.8 Appliances on Roofs. Appliances on roofs shall be
    16. 303.9 Avoiding Strain on Gas Piping. Appliances shall
    17. 303.10 Clearances. Appliances and their vent connectors
    18. 303.11 Installation in Commercial Garages. Appliances installe…
    19. 303.12 Installation in Aircraft Hangars. Heaters in aircraft h…
    20. 303.13 Pit Location. Where excavation is necessary to install
    21. 304.1 General.304.0 Accessibility for Service. Appliances shal…
    22. 304.2 Sloped Roof. Where equipment or appliances that
    23. 304.3 Access to Appliances on Roofs. Appliances
    24. 304.4 Appliances in Attics and Under-Floor Spaces.
    25. 305.3 Elevator Shaft. Unless required for the functionality
    26. 305.4 Drainage Pan. Where a water heater is located in an
    27. 305.0 Location.305.1 Installation in Garages. Appliances in re…
    28. 305.2 Flood Hazard Areas. For buildings located in flood
    29. 306.0 Automatic Control Devices.306.1 General. Heating applian…
    30. 307.0 Labeling.307.1 Fuel-Burning Appliances. Fuel-burning hea…
    31. 307.2 Electric Heating Appliances. Electric heating
    32. 307.3 Heat Pump and Electric Cooling Appliances.
    33. 307.4 Absorption Units. Absorption units shall bear a permanen…
    34. 309.2 Concealing Imperfections. It shall be unlawful to
    35. 309.3 Installation Practices. Mechanical systems shall
    36. 310.0 Condensate Wastes and Control.310.1 Condensate Disposal.…
    37. 310.2 Condensate Control. Where an equipment or appliance is i…
    38. 310.4 Appliance Condensate Drains. Condensate drain
    39. 310.5 Point of Discharge. Air-conditioning condensate
    40. 310.6 Condensate Waste From Air-ConditioningCoils. Where the c…
    41. 310.7 Plastic Fittings. Female plastic screwed fittings shall
    42. 310.3 Condensate Waste Pipe Material and Sizing.
    43. 311.2 Air Filters. Air filters shall be installed in a heating,
    44. 311.3 Prohibited Source. Outside or return air for a heating
    45. 313.2 Material. Hangers and anchors shall be of sufficient
    46. 313.3 Suspended Piping. Suspended piping or tubing
    47. 313.4 Alignment. Piping or tubing shall be supported in such
    48. 313.5 Underground Installation. Piping or tubing in the
    49. 313.6 Hanger Rod Sizes. Hanger rod sizes shall be not
    50. 313.7 Gas Piping. Gas piping shall be supported by metal
    51. 314.0 Balancing.314.1 General. Heating, ventilating, and air-c…
    52. 311.4 Return-Air Limitations. Return air from one dwelling
    53. 315.0 Louvers in Hurricane Prone Regions.315.1 General. Louver…
    54. 316.2 Installation. Piping or tubing shall be installed so that
    55. 316.3 Corrosion, Erosion, and Mechanical Damage. Piping or tub…
    56. 316.4 Protectively Coated Pipe. Protectively coated pipe
    57. 316.5 Fire-Resistant Construction. Piping, tubing, and
    58. 316.6 Steel Nail Plates. Plastic piping or tubing, copper
    59. 316.7 Sleeves. Sleeves shall be provided to protect piping
    60. 316.8 Firewalls. A pipe sleeve through a firewall shall have
    61. 316.9 Structural Members. A structural member weakened or impa…
    62. 316.10 Rodentproofing. Mechanical system shall be constructed …
    63. 316.11 Metal Collars. In or on buildings where openings
    64. 317.1 Trenches. 317.0 Trenching, Excavation, and Backfill. Tre…
    65. 317.2 Tunneling and Driving. Tunneling and driving shall
    66. 317.3 Open Trenches. Excavations required to be made for
    67. 317.4 Excavations. Excavations shall be completely backfilled …
    68. 318.2 Services/Systems and Utilities. Refer to Section
    69. 319.1 Requirements for Hospitals and Optional Serv-
    70. 319.2 Requirements for Skilled Nursing, Intermedi-
    71. 320.1 Requirements for Hospitals and Optional Serv-
    72. 320.2 Requirements for Skilled Nursing, Intermedi-
    73. 320.3 Requirements for Outpatient Facilities and
    74. 320.5 Psychiatric Services. [OSHPD 1, 1R, 2, 4 & 5 ] For proje…
    75. 321.1 (Does not apply to OSHPD 3 surgical clinic.) All heat-
    76. 321.2 All heating equipment necessary to maintain the min-
    77. 321.3 Equipment necessary for humidification of the areas
    78. 321.4 All supply, return, and exhaust fans required to maintain
    79. 321.5 All control components and control systems necessary
    80. 321.6 Alarms for airborne infection isolation rooms and pro-
    81. 322.1 The following conditions shall be met for sensitive
  4. Chapter 4 — VENTILATION AIR
  5. Chapter 5 — EXHAUST SYSTEMS
  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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