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Chapter 7 — COMBUSTION AIR

701.10 Louvers, Grilles, and Screens. The required size

California Mechanical Code (Title 24, Part 4) · 2022 edition · updated 2026-09-10 · California

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

of openings for combustion, ventilation, and dilution air shall be based on the net free area of each opening. Where the free area through a design of louver, grille, or screen is known, it shall be used in calculating the size opening required to provide the free area specified. Where the louver and grille design and free area are not known, it shall be assumed that wood louvers have 25 percent free area and metal louvers and grilles have 75 percent free area. Nonmotorized louvers and grilles shall be fixed in the open position. [NFPA 54:9.3.7.1]

701.10.1 Minimum Screen Mesh Size. Screens shall not be smaller than 1 ⁄ 4 of an inch (6.4 mm) mesh. [NFPA 54:9.3.7.2] 701.10.2 Motorized Louvers. Motorized louvers shall be interlocked with the appliance so they are proven in the full open position prior to main burner ignition and during main burner operation. Means shall be provided to

2022 CALIFORNIA MECHANICAL CODE 135

COMBUSTION AIR

prevent the main burner from igniting should the louver fail to open during burner startup and to shut down the main burner if the louvers close during burner operation.

[NFPA 54:9.3.7.3]

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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
  6. Chapter 6 — DUCT SYSTEMS
  7. ▸Chapter 7 — COMBUSTION AIR
    Overview
    1. 701.1 Applicability. Air for combustion, ventilation, and
    2. 701.2 Pressure Difference. Where used, a draft hood or a
    3. 701.3 Makeup Air. Where exhaust fans, clothes dryers, and
    4. 701.4 Indoor Combustion Air. The required volume of
    5. 701.5 Indoor Opening Size and Location. Openings
    6. 701.6 Outdoor Combustion Air. Outdoor combustion air
    7. 701.7 Combination Indoor and Outdoor Combustion
    8. 701.8 Engineered Installations. Engineered combustion
    9. 701.9 Mechanical Combustion Air Supply. Where all
    10. 701.10 Louvers, Grilles, and Screens. The required size
    11. 701.11 Combustion Air Ducts. Combustion air ducts shall
    12. 701.12 Dampers Prohibited. Combustion air ducts or
    13. 702.1 General. No device or attachment shall be installed
  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 — GEOTHERMAL ENERGY SYSTEMS
  24. Appendix G — SIZING OF VENTING SYSTEMS AND OUTDOOR COMBUSTION …
  25. Appendix H — EXAMPLE CALCULATION OF OUTDOOR AIR RATE

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