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Chapter 4 — VENTILATION AIR

414.1 Exhaust Systems. A separate, dedicated exhaust

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.

system shall be provided for airborne infection isolation rooms. The dedicated system may serve more than one air- borne infection isolation room, adjoining toilet room and anteroom. The exhaust ducts shall be identified by appro- priate labeling with the words "Caution Airborne Infection Isolation Rooms Exhaust" or similar terminology. Such labeling shall be in a manner which is not readily removable and shall appear on the exhaust duct at intervals of not more than 20 feet (6096 mm) and at least once near each room and each story traversed by the exhaust system. Exhaust fans shall comply with Section 407.1.2. The discharge from exhaust fans shall be located above the roof and shall be located a minimum of 25 feet (7620 mm) from areas that may be occupied, doors, operable windows, outdoor air intakes, or other openings into the building. The exhaust fan dis- charge shall be labeled in a manner which readily identifies the precautions which should be observed. To ensure that the airborne contaminates do not reenter the building, one of the following shall be provided:

414.1.1 Exhaust discharge from fan shall extend at least 7 feet (2134 mm) above the roof and discharge vertically upward. Self-draining stacks or equivalent shall be used for rain protection. Rain caps which divert the exhaust toward the roof shall be prohibited. 414.1.2 Exhaust shall discharge above roof level and through an accessible HEPA filter. The HEPA filter shall be located upstream of the exhaust fan and have a mini- mum efficiency of 99.97 percent based on the DOP method in accordance with Mil-Std. 282 or a minimum efficiency reporting value (MERV) of 17, based on ASHRAE 52.2. Filter gage shall be installed across the filter. For maintenance of air balance relationship, see Section 407.3.1. The 25-foot (7620 mm) dimension required by Section 414.1 may be reduced when a 99.97 percent HEPA filter or a minimum efficiency reporting value (MERV) of 17, based on ASHRAE 52.2 is used and the reduced dimension is specifically approved by the enforcing agency.

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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. 402.2 Natural Ventilation. [Not permitted for OSHPD
    2. 401.1 Applicability. This chapter contains requirements for
    3. 401.2 Filters. [BSC-CG], [DSA-SS & DSA-SS/CC] In
    4. 402.1 Occupiable Spaces. Occupiable spaces listed in
    5. 402.3 Mechanical Ventilation. [Not permitted for
    6. 402.4 Outdoor Air Intake Protection. Required outdoorair intak…
    7. 403.1 General. The design outdoor air intake flow rate for
    8. 403.2 Zone Calculations. Ventilation zone parameters
    9. 403.6 Design for Varying Operating Conditions. Ventilation sys…
    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. 403.7 Exhaust Ventilation. Exhaust airflow shall be provided i…
    14. 403.8 Dynamic Reset. The system shall be permitted to
    15. 403.9 Air Classification and Recirculation. Air shall
    16. 404.1 General. This section presents an alternative procedure …
    17. 404.2 Average Outdoor Air Fraction. The average outdoor air fr…
    18. 404.3 Zone Ventilation Efficiency. The zone ventilation
    19. 405.1 General. Rooms or occupied spaces within residential occ…
    20. 405.2 Ventilation Air Rate. The required mechanical ventilatio…
    21. 405.3 Bathroom Exhaust. A mechanical exhaust directly
    22. 405.4 Kitchen Exhaust. A mechanical exhaust directly to
    23. 405.5 Ventilation Openings. Occupiable spaces shall be
    24. 406.0 Evaporative Cooling System for Health Care
    25. 407.1 General.
    26. 407.2 Outdoor Air Intakes and Exhaust Outlets.
    27. 407.3 Air Balance.
    28. 407.4 Air Circulation.
    29. 407.5 Variable Air Volume.
    30. 407.6 Economizers. Systems with economizers shall include
    31. 408.1 General. Filter efficiencies shall be certified by the
    32. 408.2 Filters for Hospitals.
    33. 408.3 Filters for Skilled Nursing Facilities, Intermedi-
    34. 408.4 Filters for Outpatient Facilities.
    35. 409.1 Ducts which penetrate construction, intended for X-
    36. 409.2 Duct linings and their use shall meet the requirements
    37. 409.3 Insulation of Ducts. Cold air ducts shall be insu-
    38. 409.4 The anchorage and supporting structural elements for
    39. 410.1 Laboratory Ventilating Systems. Laboratory ven-
    40. 410.2 Exhaust Hoods and Safety Cabinets. Hoods and
    41. 410.3 Laboratory Fume Hoods. Laboratory fume hoods
    42. 411.1 The air from dining areas may be used to ventilate the
    43. 412.1 Boiler, heater and electrical equipment rooms shall be
    44. 412.2 Floor surfaces in occupied spaces above such rooms
    45. 413.1 Rooms in areas where excessive heat or moisture is
    46. 413.2 Kitchen, morgues and laundries located inside a hos-
    47. 414.1 Exhaust Systems. A separate, dedicated exhaust
    48. 414.2 Air Distribution. The supply outlets and exhaust
    49. 415.1 Air Distribution. The supply outlets and exhaust and
    50. 416.1 An alarm system which is based on static pressure con-
    51. 416.2 Other acceptable alarm systems will be allowed when
    52. 416.3 [For OSHPD 4] For correctional treatment centers,
    53. 416.4 Prior to acceptance of the rooms, the alarm system
    54. 417.0 Testing and Balancing Airborne Infection Isola-
    55. 418.1 Air Changes. The ETO sterilization equipment room
    56. 418.2 Exhaust Requirements.
    57. 418.3 Ventilation Requirements.
    58. 418.4 Gas Valves. Installation of gas line hand valves at the
    59. 418.5 Alarm Systems. An Audible and visual alarm system
    60. 419.1 Formula Preparation Area. Air shall be supplied
    61. 419.2 Treatment Area/Room. Air shall be supplied over
    62. 420.0 Air Distribution Devices. [OSHPD 1, 2, 3, 4 & 5]
  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 — 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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