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Earlier editions: 20222019

Chapter 5 — WATER HEATERS

506.5 Combination Indoor and 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.

Air. The use of a combination of indoor and outdoor com bustion air shall be in accordance with Section 506.5.1 through Section 506.5.3. [NFPA 54:9.3.4] (See Appendix J for example calculations) 506.5.1 Indoor Openings. Where used, openings connecting the interior spaces shall comply with Section 506.3. [NFPA 54:9.3.4(1)] 506.5.2 Outdoor Opening(s) Location. Outdoor opening(s) shall be located in accordance with Section 506.4. [NFPA 54:9.3.4(2)] 506.5.3 Outdoor Opening(s) Size. The outdoor opening(s) size shall be calculated in accordance with the following:

(1) The ratio of the interior spaces shall be the available volume of all communicating spaces divided by the required volume.

(2) The outdoor size reduction factor shall be 1 minus the ratio of interior spaces.

(3) The minimum size of outdoor opening(s) shall be the full size of outdoor opening(s) calculated in accordance with Section 506.4, multiplied by the reduction factor. The minimum dimension of air

openings shall not be less than 3 inches (76 mm).

[NFPA 54:9.3.4(3)]

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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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