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Earlier editions: 20222019

Chapter 5 — WATER HEATERS

506.4 Outdoor Combustion Air.

California Plumbing Code (Title 24, Part 5) · 2025 edition · updated 2026-09-12 · California

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

Outdoor combustion air shall be provided through opening(s) to the outdoors in accordance with the methods in Section 506.4.1 or Section 506.4.2. The minimum dimension of air openings shall not be less than 3 inches (76 mm). [NFPA 54:9.3.3] 506.4.1 Two Permanent Openings Method. Two permanent openings, one commencing within 12 inches

WATER HEATERS

FIGURE 506.4.1(1)

ALL COMBUSTION AIR FROM OUTDOORS –

INLET AIR FROM VENTILATED CRAWL SPACE AND

OUTLET AIR TO VENTILATED ATTIC

[NFPA 54: FIGURE A.9.3.3.1(1)(a)]

For SI units: 1 foot = 304.8 mm

FIGURE 506.4.1(2)

ALL COMBUSTION AIR FROM OUTDOORS

THROUGH VENTILATED ATTIC

[NFPA 54: FIGURE A.9.3.3.1(1)(b)]

FIGURE 506.4.1(3)

ALL COMBUSTION AIR FROM

OUTDOORS THROUGH HORIZONTAL DUCTS

[NFPA 54: FIGURE A.9.3.3.1(2)]

FIGURE 506.4.2

ALL COMBUSTION AIR FROM OUTDOORS THROUGH

SINGLE COMBUSTION AIR OPENING

[NFPA 54: FIGURE A.9.3.3.2]

86 2025 CALIFORNIA PLUMBING CODE

WATER HEATERS

(305 mm) of the top of the enclosure and one commencing within 12 inches (305 mm) of the bottom of the enclosure, shall be provided. The openings shall communicate directly, or by ducts, with the outdoors or spaces that freely communicate with the outdoors, as follows:

(1) Where directly communicating with the outdoors or where communicating to the outdoors through vertical ducts, each opening shall have a minimum free area of 1 square inch per 4000 Btu/h (0.0005 m [2] /kW) of total input rating of all appliances in the enclosure. [See Figure 506.4.1(1) and Figure 506.4.1(2)]

(2) Where communicating with the outdoors through horizontal ducts, each opening shall have a minimum free area of 1 square inch per 2000 Btu/h (0.001 m [2] /kW) of total input rating of all appliances in the enclosure. [NFPA 54:9.3.3.1] [See Figure 506.4.1(3)] 506.4.2 One Permanent Opening Method. One permanent opening, commencing within 12 inches (305 mm) of the top of the enclosure, shall be provided. The appliance shall have clearances of at least 1 inch (25.4 mm) from the sides and back and 6 inches (152 mm) from the front of the appliance. The opening shall directly communicate with the outdoors or shall communicate through a vertical or horizontal duct to the outdoors or spaces that freely communicate with the outdoors (see Figure 506.4.2) and shall have a minimum free area of the following: (1) One square inch per 3000 Btu/h (0.0007 m [2] /kW) of the total input rating of all appliances located in the enclosure.

(2) Not less than the sum of the areas of all vent connectors in the space. [NFPA 54:9.3.3.2]

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▸Contents — California Plumbing Code (Title 24, Part 5)
California Plumbing Code (Title 24, Part 5)
  1. Chapter 1 — GENERAL CODE PROVISIONS
  2. Chapter 2 — DEFINITIONS
  3. Chapter 3 — GENERAL REGULATIONS
  4. Chapter 4 — PLUMBING FIXTURES AND FIXTURE FITTINGS
  5. ▸Chapter 5 — WATER HEATERS
    Overview
    1. 501.1 Applicability.
    2. 501.2 California Energy Code Water Heating System
    3. 502.1 General.
    4. 503.1 Inspection of Chimneys or Vents.
    5. 503.2 Final Water Heater Inspection.
    6. 504.1 Location.
    7. 504.2 Vent.
    8. 504.3 Clearance.
    9. 504.4 Pressure-Limiting Devices.
    10. 504.5 Temperature Limiting Devices.
    11. 504.6 Temperature, Pressure, and Vacuum Relief Devices.
    12. 504.7 Lead Content.
    13. 505.1 Water Heaters.
    14. 505.2 Safety Devices.
    15. 505.3 Oil-Fired Water Heaters.
    16. 505.4 Indirect-Fired Water Heaters.
    17. 506.1 General.
    18. 506.2 Indoor Combustion Air.
    19. 506.3 Indoor Opening Size and Location.
    20. 506.4 Outdoor Combustion Air.
    21. 506.5 Combination Indoor and Outdoor Combustion Air.
    22. 506.6 Engineered Installations.
    23. 506.7 Mechanical Combustion Air Supply.
    24. 506.8 Louvers, Grilles, and Screens.
    25. 506.9 Combustion Air Ducts.
    26. 507.1 Dielectric Insulator.
    27. 507.2 Seismic Provisions.
    28. 507.3 Appliance Support.
    29. 507.4 Ground Support.
    30. 507.5 Drainage Pan.
    31. 507.6 Added or Converted Equipment or Appliances.
    32. 507.7 Type of Gas(es).
    33. 507.8 Safety Shutoff Devices for Unlisted LP-Gas Appliance Use…
    34. 507.9 Use of Air or Oxygen Under Pressure.
    35. 507.10 Protection of Gas Appliances from Fumes or Gases other …
    36. 507.11 Process Air.
    37. 507.12 Flammable Vapors.
    38. 507.13 Installation in Residential Garages.
    39. 507.14 Installation in Commercial Garages.
    40. 507.15 Installation in Aircraft Hangars.
    41. 507.16 Venting of Flue Gases.
    42. 507.17 Extra Device or Attachment.
    43. 507.18 Addition to Existing System.
    44. 507.19 Avoiding Strain on Gas Piping.
    45. 507.20 Gas Appliance Pressure Regulators.
    46. 507.21 Bleed Lines for Diaphragm-Type Valves.
    47. 508.2 Installation of Appliances on Roofs.
    48. 508.3 Appliances on Roofs.
    49. 507.22 Combination of Appliances and Equipment.
    50. 507.23 Installation Instructions.
    51. 507.24 Protection of Outdoor Appliances.
    52. 507.25 Accessibility for Service.
    53. 507.26 Clearance to Combustible Materials.
    54. 508.1 General.
    55. 508.4 Appliances in Attics and Under-Floor Spaces.
    56. 509.1 Listing.
    57. 509.2 Connection to Venting Systems.
    58. 509.3 Minimum Safe Performance.
    59. 509.4 Type of Venting System to be Used.
    60. 509.5 Masonry, Metal, and Factory-Built Chimneys.
    61. 509.6 Gas Vents.
    62. 509.7 Single-Wall Metal Pipe.
    63. 509.9 Condensation Drain.
    64. 509.10 Vent Connectors for Category I Appliances.
    65. 509.8 Through-the-Wall Vent Termination.
    66. 509.13 Manually Operated Dampers.
    67. 509.14 Automatically Operated Vent Dampers.
    68. 509.15 Obstructions.
    69. 510.1 Additional Requirements to Single Appliance Vent.
    70. 509.11 Vent Connectors for Category II, Category III, and Cate…
    71. 509.12 Appliances Requiring Draft Hoods.
    72. 510.2 Additional Requirements to Multiple-Appliance Vent.
  6. Chapter 6 — WATER SUPPLY AND DISTRIBUTION
  7. Chapter 7 — SANITARY DRAINAGE
  8. Chapter 8 — INDIRECT WASTES
  9. Chapter 9 — VENTS
  10. Chapter 10 — TRAPS AND INTERCEPTORS
  11. Chapter 11 — STORM DRAINAGE
  12. Chapter 12 — FUEL GAS PIPING
  13. Chapter 13 — HEALTH CARE FACILITIES AND MEDICAL GAS AND MEDICA…
  14. Chapter 14 — FIRESTOP PROTECTION
  15. Chapter 15 — ALTERNATE WATER SOURCES FOR NONPOTABLE APPLICATIONS
  16. Chapter 16 — NONPOTABLE RAINWATER CATCHMENT SYSTEMS
  17. Chapter 17 — REFERENCED STANDARDS
  18. Appendix A — RECOMMENDED RULES FOR SIZING THE WATER SUPPLY SYS…
  19. Appendix B — EXPLANATORY NOTES ON COMBINATION WASTE AND VENT S…
  20. Appendix C — ALTERNATE PLUMBING SYSTEMS
  21. Appendix D — SIZING STORM WATER DRAINAGE SYSTEMS
  22. Appendix E — MANUFACTURED/MOBILE HOME PARKS AND RECREATIONAL V…
  23. Appendix F — FIREFIGHTER BREATHING AIR REPLENISHMENT SYSTEMS
  24. Appendix G — SIZING OF VENTING SYSTEMS
  25. Appendix H — PRIVATE SEWAGE DISPOSAL SYSTEMS
  26. Appendix I — INSTALLATION STANDARDS
  27. Appendix J — COMBINATION OF INDOOR AND OUTDOOR COMBUSTION AND …
  28. Appendix K — POTABLE RAINWATER CATCHMENT SYSTEMS
  29. Appendix L — SUSTAINABLE PRACTICES
  30. Appendix M — PEAK WATER DEMAND CALCULATOR
  31. Appendix N — IMPACT OF WATER TEMPERATURE ON THE POTENTIAL FOR …
  32. Appendix O — NON-SEWERED SANITATION SYSTEMS
  33. Appendix P — PROFESSIONAL QUALIFICATIONS
  34. Appendix Q — INDOOR HORTICULTURAL FACILITIES
  35. Appendix R — TINY HOUSES
  36. Appendix S — ONSITE STORMWATER TREATMENT SYSTEMS

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