701.5 Indoor Opening Size and Location. Openings
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.
used to connect indoor spaces shall be sized and located in accordance with the following: (1) Each opening shall have a free area of not less than 1
square inch per 1000 Btu/h (0.002 m 2 /kW) of the total
(1) Each opening shall have a free area of not less than 1
square inch per 1000 Btu/h (0.002 m 2 /kW) of the total input rating of appliances in the space, but not less than 100 square inches (0.065 m 2 ). One opening shall commence within 12 inches (305 mm) of the top of the enclosure, and one opening shall commence within 12 inches (305 mm) of the bottom of the enclosure (see Figure 701.5). The dimension of air openings shall be not less than 3 inches (76 mm). (2) The volumes of spaces in different stories shall be con sidered as communicating spaces where such spaces are
701.4.1 Standard Method. The required volume shall be not less than 50 cubic feet per 1000 British thermal units per hour (Btu/h) (4.83 m 3 /kW). [NFPA 54:9.3.2.1] 701.4.2 Known Air Infiltration Rate Method. Where the air infiltration rate of a structure is known, the minimum required volume shall be determined as follows
[NFPA 54:9.3.2.2]: (1) For appliances other than fan-assisted, calculate
using the following Equation 701.4.2(1). [NFPA
(2) The volumes of spaces in different stories shall be con sidered as communicating spaces where such spaces are connected by one or more openings in doors or floors having a total free area of not less than 2 square inches per 1000 Btu/h (0.004 m 2 /kw) of total input rating of appliances. [NFPA 54:9.3.2.3]
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Ask AI about this code▸Contents — California Mechanical Code (Title 24, Part 4)
- Chapter 1 — GENERAL CODE PROVISIONS
- Chapter 2 — DEFINITIONS
- Chapter 3 — GENERAL REGULATIONS
- Chapter 4 — VENTILATION AIR
- Chapter 5 — EXHAUST SYSTEMS
- Chapter 6 — DUCT SYSTEMS
▸Chapter 7 — COMBUSTION AIR
Overview- 701.1 Applicability. 701.0 General. Air for combustion, ventil…
- 701.2 Pressure Difference. Where used, a draft hood or a
- 701.3 Makeup Air. Where exhaust fans, clothes dryers, and
- 701.4 Indoor Combustion Air. The required volume of
- 701.5 Indoor Opening Size and Location. Openings
- 701.6 Outdoor Combustion Air. Outdoor combustion air
- 701.7 Combination Indoor and Outdoor Combustion
- 701.10 Louvers, Grilles, and Screens. The required size
- 701.8 Engineered Installations. Engineered combustion
- 701.9 Mechanical Combustion Air Supply. Where combustion air i…
- 701.11 Combustion Air Ducts. Combustion air ducts shall
- 701.12 Dampers Prohibited. Combustion air ducts or
- 702.1 General.702.0 Extra Device or Attachment. No device or a…
- Chapter 8 — CHIMNEYS AND VENTS
- Chapter 9 — INSTALLATION OF SPECIFIC APPLIANCES
- Chapter 10 — BOILERS AND PRESSURE VESSELS
- Chapter 11 — REFRIGERATION
- Chapter 12 — HYDRONICS
- Chapter 13 — FUEL GAS PIPING
- Chapter 14 — PROCESS PIPING
- Chapter 15 — SOLAR ENERGY SYSTEMS
- Chapter 16 — STATIONARY POWER PLANTS
- Chapter 17 — REFERENCED STANDARDS
- Appendix A — RESIDENTIAL PLAN EXAMINER REVIEW FORM FOR HVAC SY…
- Appendix B — PROCEDURES TO BE FOLLOWED TO PLACE GAS EQUIPMENT …
- Appendix C — INSTALLATION AND TESTING OF OIL (LIQUID) FUEL-FIR…
- Appendix D — FUEL SUPPLY: MANUFACTURED/MOBILE HOME PARKS AND R…
- Appendix E — SUSTAINABLE PRACTICES
- Appendix F — SIZING OF VENTING SYSTEMS AND OUTDOOR COMBUSTION …
- Appendix G — EXAMPLE CALCULATION OF OUTDOOR AIR RATE