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Chapter 5 — WATER HEATERS

506.9 Combustion Air Ducts.

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.

Combustion air ducts shall comply with the following [NFPA 54:9.3.8]:

(1) Ducts shall be constructed of galvanized steel or a material having equivalent corrosion resistance, strength, and rigidity.

Exception: Within dwellings units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than one fireblock is removed. [NFPA 54:9.3.8.1]

WATER HEATERS

(2) Ducts shall terminate in an unobstructed space, allowing free movement of combustion air to the appliances.

[NFPA 54:9.3.8.2]

(3) Ducts shall serve a single space. [NFPA 54:9.3.8.3]

(4) Ducts shall not serve both upper and lower combustion air openings where both such openings are used. The separation between ducts serving upper and lower combustion air openings shall be maintained to the source of combustion air. [NFPA 54:9.3.8.4]

(5) Ducts shall not be screened where terminating in an attic space. [NFPA 54:9.3.8.5]

(6) Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located at least 12 inches (305 mm) vertically from the adjoining finished ground level.

[NFPA 54:9.3.8.8]

(7) Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air. [NFPA 54:9.3.8.6]

(8) The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory built chimney shall not be used to supply combustion air.

Exception: Direct-vent appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:9.3.8.7]

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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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