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Chapter 7 — COMBUSTION AIR

701.6 Outdoor Combustion Air. Outdoor combustion air

California Mechanical Code (Title 24, Part 4) · 2019 edition · updated 2026-09-10 · California

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

shall be provided through opening(s) to the outdoors in accordance with the methods in Section 701.6.1 or Section 701.6.2. The dimension of air openings shall be not less than 3 inches (76 mm). [NFPA 54:9.3.3]

(1) For appliances other than fan-assisted, calculate

using the following Equation 701.4.2(1). [NFPA 54:9.3.2.2(1)] (2) For fan-assisted appliances, calculate using the fol lowing Equation 701.4.2(2). [NFPA 54: 9.3.2.2(2)]

701.6.1 Two Permanent Openings Method. Two permanent openings, one commencing within 12 inches (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:

For fan-assisted appliances, calculate using the fol lowing Equation 701.4.2(2). [NFPA 54: 9.3.2.2(2)]

2019 CALIFORNIA MECHANICAL CODE 129

COMBUSTION AIR any other purpose or distributed to any other persons or parti es.

FIGURE 701.5 COMBUSTION AIR FROM ADJACENT INDOOR SPACES

THROUGH INDOOR COMBUSTION AIR OPENINGS

[NFPA 54: FIGURE A.9.3.2.3(1)]

(1) Where directly communicating with the outdoors or

where communicating to the outdoors through vertical

(1) Where directly communicating with the outdoors or

where communicating to the outdoors through vertical ducts, each opening shall have a free area of not less than 1 square inch per 4000 Btu/h (0.0005 m 2 /kW) of total input rating of appliances in the enclosure. [See Figure 701.6.1(1) and Figure 701.6.1(2)] (2) Where communicating with the outdoors through

horizontal ducts, each opening shall have a free area

(2) Where communicating with the outdoors through

horizontal ducts, each opening shall have a free area of not less than 1 square inch per 2000 Btu/h (0.001 m 2 /kW) of total input rating of appliances in the enclosure. [See Figure 701.6.1(3)] [NFPA 54:9.3.3.1] 701.6.2 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 701.6.2) 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

(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 con nectors in the space. [NFPA 54:9.3.3.2]

FIGURE 701.6.1(1) 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) COMBUSTION AIR FROM OUTDOORS

THROUGH VENTILATED ATTIC

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

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

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

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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. 701.0 General. Air for combustion, ventil…
    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. 701.10 Louvers, Grilles, and Screens. The required size
    9. 701.8 Engineered Installations. Engineered combustion
    10. 701.9 Mechanical Combustion Air Supply. Where combustion air i…
    11. 701.11 Combustion Air Ducts. Combustion air ducts shall
    12. 701.12 Dampers Prohibited. Combustion air ducts or
    13. 702.1 General.702.0 Extra Device or Attachment. No device or a…
  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 — SIZING OF VENTING SYSTEMS AND OUTDOOR COMBUSTION …
  24. Appendix G — EXAMPLE CALCULATION OF OUTDOOR AIR RATE

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