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Earlier editions: 20222019

Chapter 4 — VENTILATION AIR

403.2 Zone Calculations. Ventilation zone parameters

California Mechanical Code (Title 24, Part 4) · 2025 edition · updated 2026-09-10 · California

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

shall be determined in accordance with Section 403.2.1 through Section 403.2.3 for ventilation zones served by the ventilation system, except that the ventilation rates from ASHRAE/ASHE 170 shall be used for the occupancy categories, as applicable. [ASHRAE 62.1:6.2.1]

403.2.1 Breathing Zone Outdoor Airflow. The outdoor airflow required in the breathing zone ( Vbz ) of the occupiable space or spaces in a ventilation zone shall be not less than the value determined in accordance with Equation 403.2.1.

Vbz = Rp•Pz + Ra• Az (Equation 403.2.1)

Where: Az = zone floor area, the net occupiable floor area of the ventilation zone, ft [2] (m [2] ). Pz = zone population, the number of people in the ventilation zone during usage. Rp= outdoor airflow rate required per person (CFM/person) as determined from Table 402.1. Ra= outdoor airflow rate required per unit area (CFM/ft [2] ) as determined from Table 402.1.

[ASHRAE 62.1:6.2.1.1] For SI Units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per minute per square foot = 5.08 [(L/s)/m [2] ] 403.2.2 Zone Air Distribution Effectiveness. The zone air distribution effectiveness ( Ez ) shall be determined in accordance with Table 403.2.2. [ASHRAE 62.1:6.2.1.2] 403.2.2.1 Stratified Air Distribution Systems. A stratified air distribution system shall be designed in accordance with Section 403.2.2.1.1 through Section 403.2.2.2.2, or the zone air distribution effectiveness ( Ez ) shall be determined in accordance with ASHRAE 62.1. [ASHRAE 62.1:6.2.1.2.1] 403.2.2.1.1 Supply Air. Cool air shall be at least 4°F (2°C) less than the average room air temperature. [ASHRAE 62.1:6.2.1.2.1.1] 403.2.2.1.2 Return Air. The return air openings or pathways shall be located not less than 9 feet (2743 mm) above the floor. [ASHRAE 62.1:6.2.1.2.1.2]

403.2.2.1.3 Stratification. The zone shall not contain any devices that mechanically mix the air, and shall be protected from impinging airstreams from adjacent ventilation zones.

[ASHRAE 62.1:6.2.1.2.1.3] 403.2.2.2 Personalized Ventilation Systems. A personalized ventilation system shall be designed in accordance with the following subsections, or the zone air distribution effectiveness ( Ez ) shall be determined in accordance with ASHRAE 62.1.

[ASHRAE 62.1:6.2.1.2.2] 403.2.2.2.1 Personalized Air. The personalized air shall be distributed in the breathing zone and designed such that the velocity is

equal to or less than 50 feet per minute (0.25 m/s) at the head/facial region of the occupant.

[ASHRAE 62.1:6.2.1.2.2.1] 403.2.2.2.2 Return Air. The return air openings or pathways shall be located more than 9 feet (2.8 m) above the floor. [ASHRAE 62.1:6.2.1.2.2.2]

403.2.3 Zone Outdoor Airflow. The zone outdoor airflow ( Voz ) provided to the ventilation zone by the supply air distribution system shall be determined in accordance with Equation 403.2.3. [ASHRAE 62.1:6.2.1.3]

Voz = Vbz / Ez (Equation 403.2.3)

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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
    Overview
    1. 401.1 Applicability. This chapter contains requirements for
    2. 401.2 Indoor Swimming Pools. The design of ventilation
    3. 401.3 Filters. [BSC-CG & DSA-SS] In mechanically ven-
    4. 402.1 Occupiable Spaces. Occupiable spaces listed in
    5. 402.2 Natural Ventilation Procedure. [Not permitted
    6. 402.3 Mechanical Ventilation. [Not permitted for
    7. 402.4 Outdoor Air Intakes. Ventilation system outdoor
    8. 403.1 General. The design outdoor air intake flow rate for
    9. 403.2 Zone Calculations. Ventilation zone parameters
    10. 403.3 Single-Zone Systems. For ventilation systems
    11. 403.4 One Hundred Percent Outdoor Air Systems.
    12. 403.5 Multiple-Zone Recirculating Systems. For ventilation sys…
    13. 403.6 Design for Varying Operating Conditions. Ventilation sys…
    14. 403.7 Exhaust Ventilation. Exhaust airflow shall be provided i…
    15. 403.8 Dynamic Reset. The system shall be permitted to be
    16. 403.9 Air Classification and Recirculation. Air shall be
    17. 403.10 Air Balance. All mechanical ventilation systems
    18. 404.1 System Ventilation Efficiency. The system ventilation ef…
    19. 404.2 Average Outdoor Air Fraction. The average outdoor air fr…
    20. 404.3 Zone Ventilation Efficiency. The zone ventilation
    21. 405.1 General. Rooms or occupied spaces within residential occ…
    22. 405.2 Ventilation Air Rate. The required mechanical ventilatio…
    23. 405.3 Bathroom Exhaust. A mechanical exhaust directly
    24. 405.4 Kitchen Exhaust. A mechanical exhaust system that
    25. 405.5 Ventilation Openings. Occupiable spaces shall be
    26. 406.0 Evaporative Cooling System for Health Care
    27. 407.1 General.
    28. 407.2 Outdoor Air Intakes and Exhaust Outlets.
    29. 407.3 Air Balance.
    30. 407.4 Air Circulation.
    31. 407.5 Variable Air Volume.
    32. 407.6 Economizers.
    33. 407.7 Unoccupied Turndown.
    34. 408.3 Filters for Skilled Nursing Facilities, Intermedi-
    35. 408.4 Filters for Outpatient Facilities.
    36. 408.5 Filters for Recirculating Room Units.
    37. 409.1 Ducts which penetrate construction, intended for X-
    38. 409.2 Duct linings and their use shall meet the requirements
    39. 409.3 The anchorage and supporting structural elements for
    40. 410.1 Laboratory Ventilating Systems. Laboratory ven-
    41. 410.2 Exhaust Hoods and Safety Cabinets. Hoods and
    42. 410.3 Laboratory Fume Hoods. Laboratory fume hoods
    43. 407.8 Building Pressurization.
    44. 408.1 General. Filter efficiencies shall be certified by the
    45. 408.2 Filters for Hospitals.
    46. 411.1 The air from dining areas may be used to ventilate the
    47. 412.1 Boiler, heater and electrical equipment rooms shall be
    48. 412.2 Floor surfaces in occupied spaces above such rooms
    49. 413.1 Rooms in areas where excessive heat or moisture is
    50. 413.2 Kitchen, morgues and laundries located inside a hos-
    51. 414.1 Exhaust Systems. A separate, dedicated exhaust
    52. 414.2 Air Distribution. The supply outlets and exhaust
    53. 415.1 Air Distribution. The supply outlets and exhaust and
    54. 416.1 An alarm system which is based on static pressure con-
    55. 416.2 Other acceptable alarm systems will be allowed when
    56. 416.3 [OSHPD 4] For correctional treatment centers, the
    57. 416.4 Prior to acceptance of the rooms, the alarm system
    58. 417.0 Testing and Balancing Airborne Infection Isola-
    59. 418.1 Air Changes. The ETO sterilization equipment room
    60. 418.2 Exhaust Requirements.
    61. 418.3 Ventilation Requirements.
    62. 418.4 Gas Valves. Installation of gas line hand valves at the
    63. 418.5 Alarm Systems. An Audible and visual alarm system
    64. 419.1 Formula Preparation Area. Air shall be supplied
    65. 419.2 Treatment Area/Room. Air shall be supplied over
  5. Chapter 5 — EXHAUST SYSTEMS
  6. Chapter 6 — DUCT SYSTEMS
  7. Chapter 7 — COMBUSTION AIR
  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 — GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE…
  18. Chapter 18 — REFERENCED STANDARDS
  19. Appendix A — RESIDENTIAL PLAN EXAMINER REVIEW FORM FOR HVAC SY…
  20. Appendix B — PROCEDURES TO BE FOLLOWED TO PLACE GAS EQUIPMENT …
  21. Appendix C — INSTALLATION AND TESTING OF OIL (LIQUID) FUEL-FIR…
  22. Appendix D — FUEL SUPPLY: MANUFACTURED/MOBILE HOME PARKS AND R…
  23. Appendix E — SUSTAINABLE PRACTICES
  24. Appendix F — SIZING OF VENTING SYSTEMS AND OUTDOOR COMBUSTION …
  25. Appendix G — EXAMPLE CALCULATION OF OUTDOOR AIR RATE
  26. Appendix H — PROFESSIONAL QUALIFICATIONS
  27. Appendix I — INDOOR HORTICULTURAL FACILITIES
  28. Appendix J — CLEAN AIR DELIVERY

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