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Chapter 7 — COMBUSTION AIR

701.7 Combination Indoor and Outdoor Combustion

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.

Air. The use of a combination of indoor and outdoor combustion air shall be in accordance with Section 701.7.1 through Section 701.7.3. [NFPA 54:9.3.4] (see Appendix G

FIGURE 701.6.1(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)]

FIGURE 701.6.1(2) ALL COMBUSTION AIR FROM OUTDOORS

THROUGH VENTILATED ATTIC

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

134 2022 CALIFORNIA MECHANICAL CODE

701.7.1 Indoor Openings. Where used, openings connecting the interior spaces shall comply with Section 701.5. [NFPA 54:9.3.4(1)]

FIGURE 701.6.1(3) ALL COMBUSTION AIR FROM OUTDOORS

THROUGH HORIZONTAL DUCTS

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

701.7.2 Outdoor Opening(s) Location. Outdoor opening(s) shall be located in accordance with Section 701.6. [NFPA 54: 9.3.4(2)] 701.7.3 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 701.6, 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 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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