CRC · California Residential Code
Minimum ventilation rates and where to look them up
For a homeowner: the mechanical code requires each occupied room be given a minimum amount of fresh outdoor air based on people and floor area. Look up the space type in Table 402.1 (CMC Chapter 4) for the per‑person (Rp) and per‑square‑foot (Ra) rates, calculate Vbz = Rp×people + Ra×area per § 403.2.1, and remember that some residences and energy‑code situations use different rules (see § 401.1 and § 402.1).
Last reviewed: July 6, 2026
What the code requires — plain English
- The California Mechanical Code (Chapter 4) requires that occupiable spaces receive a minimum amount of outdoor (ventilation) air sized either per person or per area — whichever produces the larger required outdoor airflow for the space — and those occupiable spaces are listed in Table 402.1. See § 401.0 and § 402.1 for the applicability and where to look.
- The actual required breathing‑zone airflow is calculated from the per‑person rate (Rp) and the area rate (Ra) given in Table 402.1, using the zone equation in § 403.2.1.
The single most important rule: design ventilation so the required breathing‑zone outdoor air (Vbz) is not less than Rp × Pz + Ra × Az, using the Rp/Ra values in Table 402.1 for the listed occupancies.
Requirements in detail
Which sections are the controlling references
- § 401.0 General — declares Chapter 4 covers ventilation, applicability, and notes dwelling units and other exceptions.
- § 402.1 Occupiable Spaces — states occupiable spaces listed in Table 402.1 must be provided ventilation air and points you to the Table; it also tells you the California Energy Code (CEC) can supersede the CMC for some occupancies.
Key calculation rule and locations to look
- Use Equation in § 403.2.1: Vbz = Rp × Pz + Ra × Az (where Rp = cfm/person from Table 402.1, Ra = cfm/ft2 from Table 402.1, Pz = occupants in the zone, Az = zone net floor area). § 403.2.1 and Table 402.1 are your calculation sources.
Decision‑relevant quick table (pick the larger of the Rp or Ra result)
| Occupancy (example) | Rp (cfm/person) | Ra (cfm/ft²) | Default occupant density (people/1000 ft²) | Code Reference |
|---|---|---|---|---|
| Office space | 5 | 0.06 | 5 | Table 402.1 — see § 402.1. |
| Bedroom / living room (dwellings) | 5 | 0.06 | 10 | Table 402.1; dwelling unit ventilation rates may be covered by § 405.0 or ASHRAE 62.2 (see § 401.1). |
| Conference / meeting room | 5 | 0.06 | 50 | Table 402.1 — use Rp and default density unless fixed seating provided. |
| Kitchen (within dwelling unit — local exhaust) | (local exhaust requirements separate) | — | — | Local kitchen/bath exhaust minimums and exceptions referenced in CRC and CMC; see § 402.1 and CRC R325 notes. |
Notes on the table:
- Table entries above are drawn directly from Table 402.1 (CMC). Use the Rp and Ra values from that Table for calculations.
- If occupancy is unknown, use the default occupant density column from Table 402.1 to compute Pz.
Exceptions & special cases
- California Energy Code (CEC) allocations: ventilation requirements for occupancies regulated by the California Energy Commission are found in the Energy Code and supersede the Mechanical Code where applicable — see § 402.1. Always check if CEC provisions (e.g., Sections 120.1 / 150.0) apply before carrying out Chapter 4 calculations.
- Dwelling units: Chapter 4 excludes the ventilation‑rate method for dwelling units where occupants are nontransient; those follow § 405.0 or ASHRAE 62.2 per § 401.1. Do not apply the nonresidential Table 402.1 Rp/Ra method to a typical single‑family dwelling unless specifically required.
- Health care spaces: Use Table 4‑A or ASHRAE/ASHE 170 for health care; where both apply, use the more restrictive rate (see § 402.1).
- Natural ventilation: If using natural (window) ventilation, follow the CMC natural ventilation procedure and the minimum openable areas in Section 402.2 and associated tables — natural ventilation is an alternative method but has its own measurements/assumptions.
- Filters: When mechanically ventilated, the code directs MERV‑13 filtration for regularly occupied areas in mechanically ventilated buildings (see § 401.3).
Common mistakes
- Assuming ventilation = area only. The code requires combining the per‑person (Rp) and per‑area (Ra) contributions — use the equation in § 403.2.1, not just A × Ra.
- Using residential (ASHRAE 62.2 / § 405.0) methods for nonresidential spaces — or the reverse. Check § 401.1 and § 402.1 to confirm which method applies.
- Forgetting to record ventilation rates and distribution assumptions on construction documents — § 402.1.1 requires the outdoor air rate and distribution assumptions be shown. Missing documentation is a frequent review comment.
- Not checking whether the CEC (Energy Code) rules supersede the CMC for the building type — § 402.1 warns that CEC provisions may govern.
Worked example — small office, step by step
Scenario: a 1,000 ft² private office area with no fixed seating; default occupant density from Table 402.1 for "office space" is 5 people/1000 ft².
- Determine Pz (expected occupants): default = 5 people (1,000 ft² × 5/1000). Table 402.1.
- Read Rp and Ra from Table 402.1 for office: Rp = 5 cfm/person, Ra = 0.06 cfm/ft².
- Apply the equation in § 403.2.1: Vbz = Rp × Pz + Ra × Az.
- Per‑person term: 5 cfm/person × 5 people = 25 cfm.
- Area term: 0.06 cfm/ft² × 1,000 ft² = 60 cfm.
- Required ventilation (sum): 85 cfm delivered to the breathing zone.
- Document: show 85 cfm (and the Rp/Ra assumptions) on the construction documents as required by § 402.1.1.
If the system serves multiple rooms/zones, perform the zone calculation per § 403.2 and aggregate as required.
Where to look in the code (related provisions)
- § 401.0 — General (purpose, scope, dwelling‑unit note).
- § 402.1 — Occupiable spaces and Table 402.1 reference (what spaces are covered).
- Table 402.1 — Minimum ventilation rates (Rp, Ra, default densities) — the primary lookup for rates.
- § 403.2.1 — Breathing‑zone outdoor airflow equation (Vbz = Rp·Pz + Ra·Az).
- § 402.2 — Natural ventilation procedure and minimum openable areas.
- § 402.3 — Mechanical ventilation requirements and controls where natural ventilation is not used.
- § 401.3 — Filtration (MERV‑13 requirement for mechanically ventilated regularly occupied areas).
- § 405.0 — Ventilation requirements that specifically apply to dwelling units (and ASHRAE 62.2 reference).
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 62.1 High relevance — show source text
MINIMUM VENTILATION RATES IN BREATHING ZONE
[ASHRAE 62.1: TABLE 6-1]
OCCUPANCY CATEGORY PEOPLE OUTDOOR
Air Rate Rp
(CFM/person)AREA OUTDOOR
Air Rate Ra
(CFM/ft2)DEFAULT OCCUPANT
DENSITY
(people/1000 ft2)AIR CLASS MISCELLANEOUS SPACES MISCELLANEOUS SPACES MISCELLANEOUS SPACES MISCELLANEOUS SPACES MISCELLANEOUS SPACES Banks or bank lobbies 7.5 0.06 15 1 Bank vaults/safe deposit 5 0.06 5 2 Computer (not printing) 5 0.06 4 1 Freezer and refrigerated spaces (<50°F) 10 0 0 2 Manufacturing where hazardous materials
are not used10 0.18 7 2 Manufacturing where hazardous materials
are used (excludes heavy industrial and
chemical processes)10 0.18 7 3 Pharmacy (prep. area) 5 0.18 10 2 Photo studios 5 0.12 10 1 Shipping/receiving 10 0.12 2 2 Sorting, packing, light assembly 7.5 0.12 7 2 Telephone closets – 0.00 – 1 Transportation waiting 7.5 0.06 100 1 Warehouses 10 0.06 – 2 OFFICE BUILDINGS OFFICE BUILDINGS OFFICE BUILDINGS OFFICE BUILDINGS OFFICE BUILDINGS Break Rooms 5 0.12 50 1 Main entry lobbies 5 0.06 10 1 Occupiable storage rooms for dry materials 5 0.06 2 1 Office space 5 0.06 5 1 Reception areas 5 0.06 30 1 Telephone/data entry 5 0.06 60 1 OUTPATIENT HEALTH CARE FACILITIES1,2,3 OUTPATIENT HEALTH CARE FACILITIES1,2,3 OUTPATIENT HEALTH CARE FACILITIES1,2,3 OUTPATIENT HEALTH CARE FACILITIES1,2,3 OUTPATIENT HEALTH CARE FACILITIES1,2,3 Birthing room 10 0.18 15 2 Class 1 imaging rooms 5 0.12 5 1 Dental operatory 10 0.18 20 1 General examination room 7.5 0.12 20 1 Other dental treatment areas 5 0.06 5 1 Physical therapy exercise area 20 0.18 7 2 Physical therapy individual room 10 0.06 20 1 Physical therapeutic pool area – 0.48 – 2 Prosthetics and orthotics room 10 0.18 20 1 Psychiatric consultation room 5 0.06 20 1 Psychiatric examination room 5 0.06 20 1 Psychiatric group room 5 0. CRC § 0.18 High relevance — show source text
5|0.18|70|2| |GENERAL|GENERAL|GENERAL|GENERAL|GENERAL| |Break rooms|5|0.06|25|1| |Coffee stations|5|0.06|20|1| |Conference/meeting|5|0.06|50|1| |Corridors|–|0.06|–|1| |Occupiable storage rooms for liquids or gels|5|0.12|2|2| |HOTELS, MOTELS, RESORTS, DORMITORIES|HOTELS, MOTELS, RESORTS, DORMITORIES|HOTELS, MOTELS, RESORTS, DORMITORIES|HOTELS, MOTELS, RESORTS, DORMITORIES|HOTELS, MOTELS, RESORTS, DORMITORIES| |Barracks sleeping areas|5|0.06|20|1| |Bedroom/living room|5|0.06|10|1| |Laundry rooms, central|5|0.12|10|2| |Laundry rooms within dwelling units|5|0.12|10|1| |Lobbies/prefunction|7.5|0.06|30|1| |Multipurpose assembly|5|0.06|120|1|
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VENTILATION AIR
TABLE 402.1 (continued)
MINIMUM VENTILATION RATES IN BREATHING ZONE
[ASHRAE 62.1: TABLE 6-1]
OCCUPANCY CATEGORY PEOPLE OUTDOOR
Air Rate Rp
(CFM/person)AREA OUTDOOR
Air Rate Ra
(CFM/ft2)DEFAULT OCCUPANT
DENSITY
(people/1000 ft2)AIR CLASS MISCELLANEOUS SPACES MISCELLANEOUS SPACES MISCELLANEOUS SPACES MISCELLANEOUS SPACES MISCELLANEOUS SPACES Banks or bank lobbies 7.5 0.06 15 1 Bank vaults/safe deposit 5 0.06 5 2 Computer (not printing) 5 0.06 4 1 Freezer and refrigerated spaces (<50°F) 10 0 0 2 Manufacturing where hazardous materials
are not used10 0.18 7 2 Manufacturing where hazardous materials
are used (excludes heavy industrial and
chemical processes)10 0.18 7 3 Pharmacy (prep. area) 5 0.18 10 2 Photo studios 5 0.12 10 1 Shipping/receiving 10 0.12 2 2 Sorting, packing, light assembly 7.5 0.12 7 2 Telephone closets – 0.00 – 1 Transportation waiting 7.5 0.06 100 1 Warehouses 10 0. CRC § 62.1 High relevance — show source text
Controls shall be designed to coordinate operation of the natural and mechanical ventilation systems. [ASHRAE 62.1:6.4.3] D. Naturally ventilated spaces shall also include a mechanical ventilation system designed in accordance with Section 120.1(c)3. Exception 1 to Section 120.1(c)2D: Spaces not served by a space-conditioning system. Exception 2 to Section 120.1(c)2D: Spaces where natural ventilation openings complying with Section 120.1(c)2 are either permanently open or have controls that prevent the openings from being closed during periods of expected occupancy. 3. Mechanical ventilation. Occupiable spaces shall be ventilated with a mechanical ventilation system capable of providing an outdoor airflow rate to the zone ( V z ) no less than Equation 120.1-F as described below:
(Equation 120.1-F) V z = The larger of R p × P z or R a × A z
Where:
R p = 15 cubic feet per minute of outdoor airflow per person P z = The expected number of occupants. For spaces without fixed seating, the expected number of occupants shall be the expected number specified by the building designer or the default occupancy density in Table 120.1-A times the occupiable floor area of the zone, whichever is greater. For spaces with fixed seating, the expected number of occupants shall be determined in accordance with Section 1004.6 of the California Building Code. R a = The area-based minimum ventilation airflow rate in Table 120.1-A. A z = The net occupiable floor area of the ventilation zone in square feet.
Exception 2 to Section 120.1(c)3: Transfer air. The rate of outdoor air required by Section 120.1(c)3 may be provided with air transferred from other ventilated space if: A. Use of transfer air is in accordance with Section 120.1(g); and B. The outdoor air that is supplied to all spaces combined, is sufficient to meet the requirements of Section 120.1(c)3 for each space individually. 4. Exhaust ventilation. The design exhaust airflow shall be determined in accordance with the requirements in Table 120.1-B. Exhaust makeup air shall be permitted to be any combination of outdoor air, recirculated air, or transfer air.
[ASHRAE 62.1:6.5.1]
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NONRESIDENTIAL, HOTEL/MOTEL OCCUPANCIES, AND COVERED PROCESSES—MANDATORY REQUIREMENTS
TABLE 120.1-A—MINIMUM VENTILATION RATES Col2 Col3 Col4 Col5 OCCUPANCY CATEGORY MINIMUM OCCUPANT LOAD
DENSITY (persons/1,000 ft2)AREA-BASED MINIMUM
VENTILATION_ Ra_ (cfm/ft2)AIR CLASS NOTES Educational Facilities Educational Facilities Educational Facilities Educational Facilities Educational Facilities Daycare (through age 4) 14 0. CRC § 453.4.7 High relevance — show source text
453.4.7 Ventilation.
453.4.7.1 Compatibility. Incompatible materials shall not be conveyed in the same duct system. Combined products in mechani- cal exhaust ducts shall not create a physical hazard or reaction that could degrade the duct material. The building official may require a technical report in accordance with Section 453.7.1.
453.4.7.2 Fire dampers, smoke dampers and combination fire/smoke dampers. Fire dampers, smoke dampers or fire/smoke dampers shall not be permitted in mechanical exhaust duct systems used to maintain a safe laboratory environment. When the exhaust duct penetrates the laboratory suite boundary the exhaust duct shall be located within a horizontal or vertical assembly having a fire resistance rating equal to the fire barrier.
453.4.7.3 Reserved.
453.4.7.4 Laboratory suite exhaust air.
453.4.7.4.1 Exhaust air from laboratory suites shall not be recirculated.
453.4.7.4.2 Laboratory suite exhaust air shall be independently ducted to a point outside the building or an approved roof top structure.
Exception: Exhaust ducts serving separate laboratory suites may be connected to a common duct within a fire rated verti- cal shaft when the sub-duct extends vertically upward at least 22 inches.
453.4.7.4.3 Laboratory suite exhaust ducts shall not penetrate the fire barriers required by Section 453.4.1.
Exception: Where the exhaust duct is enclosed in a rated shaft in accordance with Section 713.
453.4.7.5 Ventilation rates. Mechanical exhaust ventilation systems shall provide a minimum ventilation rate not less than 1 cubic feet per minute per square foot [0.00508 m [3] /(s·m [2] ) ] of floor area, or 6 air exchanges per hour, whichever is greater. Systems shall operate continuously at the designed ventilation rate.
Exception: Refer to California Fire Code Section 5001.3 Performance-based design alternatives, as approved by the Fire Code Official.
453.4.7.6 Reserved.
453.4.7.7 Mechanical ventilation system balancing. Mechanical ventilation systems shall be designed and balanced such that during normal and emergency conditions the door opening forces comply with the requirements of Sections 1010.1.3 and Chapter 11B as applicable. Emergency conditions shall include: supply fan shutdown or failure, closing of smoke dampers or combination fire/smoke dampers, or emergency power.
453.5 Fire protection systems. See Chapter 9.
453.6 Means of egress.
453.6.1 Access to exits. Every room of a laboratory suite containing hazardous materials and having a floor area of 500 square feet (19 m2) or more shall have access to not less than two separate exits or exit-access doorways in accordance with Section 1006.2.
453.6.2 Door swing. All exit and exit-access doors serving areas with hazardous materials shall swing in the direction of exit travel, regardless of the occupant load served.
CRC § 0.0283 High relevance — show source text
For SI units: 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] ], 1 square foot = 0.0929 m [2]
Where:
Vbz = breathing zone outdoor airflow, per Table 402.1. Az = zone floor area, the net occupiable floor area of the ventilation zone. W S = aggregated width of all single outdoor openings located at the same elevation.
H S = vertical dimension of the single opening or the least vertical dimension of the openings where there are multiple openings.
Volumetric airflow rates used to estimate required openable area are based on the following:
Dry-air density of 0.075 lbda/ft [3] (1.2 kgda/m [3] ) at a barometric pressure of 1 atm (101.3 kPa) and an air temperature of 70°F (21°C)
Temperature difference between indoors and outdoors of 1.8°F (1°C)
Gravity constant of 32.2 ft/s [2] (9.81m/s [2] )
Window discharge coefficient of 0.6
(2) Determine the effect of pressure losses along natural ventilation airflow paths on the resulting flow rates, including inlet openings, air transfer grills, ventilation stacks, and outlet openings during representative conditions of expected natural ventilation system use.
(3) Quantify natural ventilation airflow rates of identified airflow paths accounting for wind induced and thermally induced driving pressures during representative conditions of expected natural ventilation system use.
(4) Design to provide outdoor air in quantities sufficient to result in acceptable IAQ as established under Section 403.2.1 or ASHRAE 62.1 during representative conditions of expected natural ventilation system use. {ASHRAE 62.1:6.4.2}
402.2.3 Control and Accessibility. The means to open required operable openings shall be readily accessible to building occupants whenever the space is occupied. Controls shall be designed to coordinate operation of the natural and mechanical ventilation systems.
[ASHRAE 62.1:6.4.3]
402.3 Mechanical Ventilation. [Not permitted for OSHPD 1, 2, 3, 4 & 5] Where natural ventilation is not permitted by this section or the California Building Standards Code, mechanical ventilation systems shall be designed, constructed, and installed to provide a method of supply air and either return air or exhaust air, or both, as applicable. Mechan
|Col1|TABLE 402.2.1.6(A)(2) MINIMUM OPENABLE AREAS: TWO VERTICALLY SPACED OPENINGS* [ASHRAE 62.
CRC § 405.4.1 High relevance — show source text
instructions.
405.4.1 Exhaust Rate. For intermittent-controlled operations, the exhaust rate shall be not less than 100 ft [3] /min (47.2 L/s) for range hoods or 300 ft [3] /min (142 L/s) for mechanical exhaust fans including downdraft appliances. For continuous operated ventilation, the exhaust rate shall be not less than 50 ft [3] /min (23.6 L/s). 405.5 Ventilation Openings. Occupiable spaces shall be provided with a readily accessible ventilation opening openable to the outdoors. The opening shall be not less than 5 square feet (0.464 m [2] ) or 4 percent of the occupied floor area. The openable area shall be based on free, unobstructed area through the opening.
2025 CALIFORNIA MECHANICAL CODE 77
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VENTILATION AIR
406.0 Evaporative Cooling System for Health Care Facilities. [OSHPD 1, 2, 3, 4 & 5] Direct evaporative cool- ing systems where the air directly contacts the wetted surface or spray shall be limited in health facilities to nonpatient areas such as laundry rooms, and boiler or machinery rooms. Similar rooms with high heating-producing equipment will be consid- ered when specifically approved by the enforcing agency. The evaporative pads shall be a synthetic type. Filters shall be required in accordance with Tables 4-B and 4-C except utility rooms, i.e.: boiler or machinery rooms.
407.0 Ventilation System Details. [OSHPD 1, 1R, 2, 3, 4 & 5]
407.1 General.
407.1.1 All supply-air, return air, and exhaust-air sys- tems shall be mechanically operated and such systems for areas listed in Table 4-A shall be operated continu- ously. Natural ventilation through windows or other openings such as louvers will be considered as supple- mental to the required mechanical ventilation systems.
Exceptions:
(1) Natural ventilation shall not be used in airborne infection isolation rooms and protective environment
rooms.
(2) Unoccupied turndown shall be permitted in accor- dance with Section 407.7.
407.1.2 Fans serving exhaust systems shall be located at the discharge end of the system. Ductwork within the building shall be under negative pressure. The ventilation rates shown in Table 4-A shall be considered as minimum acceptable rates and shall not be construed as precluding the use of higher ventilation rates if they are required to meet design conditions. 407.1.3 Services/Systems and Utilities. (Refer to Sec- tion 1224.4.1 of the California Building Code).
407.2 Outdoor Air Intakes and Exhaust Outlets.
407.2.1 Outdoor Air Intakes. Outdoor air intakes shall be located at least 25 feet (7.62 m) from exhaust outlets of ventilating systems, combustion equipment stacks, med- ical-surgical vacuum systems, cooling towers, and areas that may collect vehicular exhaust or other noxious _fumes.
CRC § 150.0 High relevance — show source text
ii. Outdoor air damper(s) . A motorized damper(s) shall be installed on the connected ventilation duct(s) of CFI systems that prevents all airflow into or out of the space-conditioning duct system when the damper(s) is closed.
iii. Damper control . The required motorized damper(s) shall be controlled to be in an opened position when outdoor air ventilation is required for compliance, and shall be in the closed position when ventilation air is not required. The damper(s) shall be closed whenever the space-conditioning system air handling unit is not operating. If the outdoor airflow for the CFI ventilation system is fan-powered, then the outdoor air fan shall not operate when the required motorized damper(s) on the outdoor air ventilation duct(s) is closed. iv. Variable ventilation. CFI ventilation systems shall incorporate controls that track outdoor air ventilation run time, and either open or close the required motorized damper(s) depending on whether or not outdoor air ventilation is required for compliance with Section 150.0(o)1C. During periods when comfort conditioning is not called for by the space-conditioning thermostat, the CFI ventilation system controls shall operate the spaceconditioning system central fan and outdoor air damper(s) when necessary to ensure compliance with the minimum outdoor air ventilation required by Section 150.0(o) in accordance with applicable variable mechanical ventilation methods specified in ASHRAE 62.2 Section 4.5. C. Whole-dwelling unit mechanical ventilation for single-family dwellings. Single-family dwellings shall have mechanical ventilation as specified in Subsections i and iv. Single-family detached dwelling units and attached dwelling units not sharing ceilings or floors with other dwelling units, occupiable spaces, public garages, or commercial spaces may reduce their required mechanical ventilation rates in accordance with Subsections ii and iii. Vertically attached dwelling units shall not reduce their minimum ventilation rates in accordance with Subsections ii and iii.
i. Total Required Ventilation Rate [ASHRAE 62.2:4.1.1]. The total required ventilation rate shall be calculated using Equation 150.0-B. (Equation 150.0-B) Q tot = 0.03 A floor + 7.5( N br + 1)
where:
Q tot = total required ventilation rate, cfm A floor = dwelling-unit floor area, ft [2]
N br = number of bedrooms (not to be less than 1) ii. Effective Annual Average Infiltration Rate. The effective annual average infiltration rate shall be determined in accordance with Subsections a and b:
a. An enclosure leakage rate in cubic feet per minute at 50 Pa (0.2 inch water) ( Q 50 ) shall be determined by either Subsection 1 or Subsection 2 below.
- Q 50 shall be calculated based on the conditioned volume of the dwelling unit and a default value for dwelling unit envelope leakage of 2 air changes per hour at 50 PA (0.2 inch water) (2 ACH 50 ) as specified by Equation 150.0-C below. (Equation 150.0-C) Q 50 = V du x 2 ACH 50 /60 min
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CRC § 2.1 High relevance — show source text
Exception: The glazed areas shall not be required where artificial light and a local exhaust system are provided. The minimum local exhaust rates shall be 50 cubic feet per minute (25 L/s) for intermittent ventilation or 20 cubic feet per minute (10 L/s) for contin- uous ventilation in accordance with the California Mechanical Code, Chapter 4 . Exhaust air from the space shall be exhausted directly to the outdoors.
R325.2.1 Bathroom exhaust fans. Each bathroom containing a bathtub, shower or tub/shower combination shall be mechanically ventilated for purposes of humidity control in accordance with the California Mechanical Code, Chapter 4; and the California Green Building Standards Code, Chapter 4, Division 4.5.
Note: Window operation is not a permissible method of providing bathroom exhaust for humidity control.
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BUILDING PLANNING
R325.3 Ventilation. Ventilation air rates shall be in compliance with the California Mechanical Code.
R325.4 Opening location. Outdoor intake and exhaust openings shall be located in accordance with Sections R325.4.1 and R325.4.2.
R325.4.1 Intake openings. Mechanical and gravity outdoor air intake openings shall be located not less than 10 feet (3048 mm) from any hazardous or noxious contaminant, such as vents, chimneys, plumbing vents, streets, alleys, parking lots and loading docks.
For the purpose of this section, the exhaust from dwelling unit toilet rooms, bathrooms and kitchens shall not be considered as hazardous or noxious.
Exceptions:
The 10-foot (3048 mm) separation is not required where the intake opening is located 3 feet (914 mm) or greater below the contaminant source.
Vents and chimneys serving fuel-burning appliances shall be terminated in accordance with the applicable provisions of the California Mechanical Code.
Clothes dryer exhaust ducts shall be terminated in accordance with the California Mechanical Code.
R325.4.2 Exhaust openings. Exhaust air shall not be directed onto walkways.
R325.5 Outside opening protection. Air exhaust and intake openings that terminate outdoors shall be protected with corrosionresistant screens, louvers or grilles having an opening size of not less than [1] / 4 inch (6 mm) and a maximum opening size of [1] / 2 inch (13 mm), in any dimension. Openings shall be protected against local weather conditions. Outdoor air exhaust and intake openings shall meet the provisions for exterior wall opening protectives in accordance with this code.
R325.6 Interior stairway illumination. Interior stairways shall be provided with an artificial light source to illuminate the landings and treads. The light source shall be capable of illuminating treads and landings to levels of not less than 1 footcandle (11 lux) as measured at the center of treads and landings. There shall be a wall switch at each floor level to control the light source where the stairway has six or more risers.
Exception: A switch is not required where remote, central or automatic control of lighting is provided.
CRC § 160.2 Medium relevance — show source text
c. When a single zone damper or a single zone system serves multiple spaces, there shall be an occupant sensor in each space and the zone shall not be considered vacant until all spaces in the zone are vacant. d. One hour prior to normal scheduled occupancy, the occupant sensor ventilation control shall allow preoccupancy purge as described in Section 160.2(c)5B. e. When the zone is scheduled to be occupied and occupant sensing controls in all spaces served by the zone indicate the spaces are unoccupied, the zone shall be placed in occupied-standby mode. f. In 5 minutes or less after entering occupied-standby mode, mechanical ventilation to the zone shall be shut off until the space becomes occupied or until ventilation is needed to provide space heating or conditioning. When mechanical ventilation is shut off to the zone, the ventilation system serving the zone shall reduce the system outside air rate by the amount of outside air required for the zone. g. Where the system providing space conditioning also provides ventilation to the zone, in 5 minutes or less after entering occupied-standby mode, space-conditioning zone setpoints shall be reset in accordance with Section 120.2(e)3. 6. Ducting for zonal heating and cooling units. Where a return plenum is used to distribute outdoor air to a zonal heating or cooling unit that then supplies the air to a space in order to meet the requirements of Section 160.2(c)3, the outdoor air shall be ducted to discharge either: A. Within 5 feet of the unit; or
B. Within 15 feet of the unit, substantially toward the unit and at a velocity not less than 500 feet per minute. 7. Design and control requirements for quantities of outdoor air . A. All mechanical ventilation and space-conditioning systems shall be designed with and have installed ductwork, dampers and controls to allow outside air rates to be operated at the minimum levels specified in Section 160.2(c)3 or the rate required for make-up of exhaust systems that are required for an exempt or covered process, for control of odors or for the removal of contaminants within the space. B. All variable air volume mechanical ventilation and space-conditioning systems shall include dynamic controls that maintain measured outside air ventilation rates within 10 percent of the required outside air ventilation rate at both full and reduced supply airflow conditions. Fixed minimum damper position is not considered to be dynamic and is not an allowed control strategy. C. Measured outdoor air rates of constant volume mechanical ventilation and space-conditioning systems shall be within 10 percent of the required outside air rate.
8. Air classification and recirculation limitations. Air classification and recirculation limitations of air shall be based on the air classification as listed in Table 160.2-B or Table 160.2-D, in accordance with the following: A. Class 1 air is air with low contaminant concentration, low sensory-irritation intensity or inoffensive odor. Recirculation or transfer of Class 1 air to any space shall be permitted; [ASHRAE 62.1:5.13.3.1] B. Class 2 air is air with moderate contaminant concentration, mild sensory-irritation intensity or mildly offensive odor (Class 2 air also includes air that is not necessarily harmful or objectionable but that is inappropriate for transfer or recirculation to spaces used for different purposes).
CRC § 805.6 Medium relevance — show source text
(6) Where the economizer is disabled, the outdoor air damper closes to a minimum position; the return damper modulates 100 percent open, and mechanical cooling remains enabled. E 805.6 Demand-Controlled Ventilation Systems Acceptance (Form MECH-6A). The purpose of this test is to verify that systems required to employ demand-controlled ventilation shall be permitted to vary outside ventilation flow rates based on maintaining interior carbon dioxide (CO 2 ) concentration setpoints. Demand-controlled ventilation refers to an HVAC system’s ability to reduce outdoor air ventilation flow below design values where the space served is at less than design occupancy. Carbon dioxide is a good indicator of occupancy load and is the basis used for modulating ventilation flow rates.
E 805.6.1 Test Procedure. The procedure for performing a functional test for demand-control ventilation (DVC) systems shall be in accordance with Section E 805.6.1.1 and Section E 805.6.1.2.
E 805.6.1.1 Construction Inspection. Prior to functional testing, verify and document the following:
(1) Carbon dioxide control sensor is factory calibrated or field-calibrated in accordance with this appendix.
(2) The sensor is located in the high-density space between 3 feet (914 mm) and 6 feet (1829 mm) above the floor or at the anticipated level of the occupants’ heads.
(3) DCV control setpoint is at or below the carbon dioxide concentration permitted by this appendix.
E 805.6.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:
Step 1: Disable economizer controls.
Step 2: Simulate a signal at or slightly above the carbon dioxide concentration setpoint required by this appendix. Verify and document the following:
(1) For single zone units, outdoor air damper modulates open to satisfy the total ventilation air called for in the certificate of compliance.
(2) For multiple zone units, either outdoor air damper or zone damper modulate open to satisfy the zone ventilation requirements.
Step 3: Simulate signal well below the carbon dioxide setpoint. Verify and document the following:
(1) For single zone units, outdoor air damper modulates to the design minimum value.
(2) For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation requirements.
Step 4: Restore economizer controls and remove system overrides initiated during the test.
Step 5: With controls restored, apply carbon dioxide calibration gas at a concentration slightly above the setpoint to the sensor. Verify that the outdoor air damper modulates open to satisfy the total ventilation air called for in the certificate of compliance.
E 805.6.2 Acceptance Criteria. Demand-controlled ventilation systems acceptance criteria shall be as follows:
(1) Each carbon dioxide sensor is factory calibrated (with calibration certificate) or field calibrated.
(2) Each carbon dioxide sensor is wired correctly to the controls to ensure proper control of the outdoor air damper.
(3) Each carbon dioxide sensor is located correctly within the space 1 foot (305 mm) to 6 feet (1829 mm) above the floor.
(4) Interior carbon dioxide concentration setpoint is not more than 600 parts per million (ppm) plus outdoor air carbon dioxide value where dynamically measured or not more than 1000 ppm where no OSA sensor is provided.
CRC § 0.30 Medium relevance — show source text
CK105.1 Windows, minimum size and dimensions. A minimum of one window shall be provided that meet the minimum size, mini- mum dimensions and operational constraints of Section R310. The number of such windows shall be appropriate for the occupancy or occupancies of the portions of the building that are below WSEL200.
Note: It is the intent of this section that windows be of sufficient number, sizes and dimensions to reasonably accommodate the needs and limitations of the occupants of the building. Reasonable judgment in the application of this requirement must be exer- cised by the building official.
CK105.2 Exterior doors to decks, balconies and porches. Exterior doors to decks, balconies and porches shall be sized in accor- dance with Section R311.
CK105.3 Means of escape to rooftops from spaces within a building. The means of escape to rooftops shall be permitted to be provided by a stairway, ramp, alternating tread device, fixed ladder or other means approved by the building official.
CK106 Decks and balconies that are evacuation locations. Decks and balconies that have finish floors no less than one (1) foot (0.30 meter) above the WSEL200 shall be permitted to be evacuation locations. When a deck or balcony used as an evacuation location is not at the same level as a floor within the building, it shall be permitted to be accessed by a stairway, ramp, alternating tread device, fixed ladder or other means approved by the building official.
CK106.1 Live load. Decks and balconies that are evacuation locations shall be designed for the live load required in Table R301.5.
CK106.2 Evacuation route. Evacuation routes to decks and balconies that are evacuation locations shall be permitted to be provided by a stairway, ramp, alternating tread device, fixed ladder or other means approved by the building official.
CK107 Rooftop evacuation locations. Rooftop evacuation locations shall be permitted to include rooftop platforms and rooftop areas provided that they are no less than one (1) foot (0.30 meter) above the WSEL200. A minimum horizontal distance of 3 feet (0.91 meter) shall be provided between the lower edge of the rooftop evacuation location access point and the evacuation location lower perimeter.
CK107.1 Rooftop platforms required. A rooftop platform shall be provided if the roof covering materials are: 1. Clay tile, concrete tile, slate shingles, wood shingles or wood shakes and the roof slope is three units vertical in 12 units hori- zontal (25 percent slope) or greater. 2. Metal roof panels or metal roof shingles and the roof slope is one unit vertical in 12 units horizontal (8.33 percent slope) or greater.
CK107.2 Roof live loads. Roof areas that are rooftop evacuation locations and roofs that support rooftop platforms that are evacua- tion locations shall be designed for the roof live load required for the occupancy as required in CBC Table 1607.2.
CK107.3 Evacuation routes to rooftop evacuation locations. Evacuation routes to rooftop evacuation locations shall be permitted to be provided by a stairway, ramp, alternating tread device, fixed ladder or other means approved by the building official.
APPENDIX CK-4 2025 CALIFORNIA RESIDENTIAL CODE
CRC § 11.5 Medium relevance — show source text
Water|ARI 325| |Groundwater source heat pump*|Cooling Mode|11.5_EER_ at 50°F Ent. Water|11.5_EER_ at 50°F Ent. Water| |Groundwater source heat pump*|Heating Mode|3.4_COP_ at 70°F Ent. Water|3.4_COP_ at 70°F Ent. Water| |Groundwater source heat pump*|Heating Mode|3.0_COP_ at 50°F Ent. Water|3.0_COP_ at 50°F Ent. Water| |Unitary A/C|Water cooled split system|9.3_EER_ at 85°F Ent. Water|ARI 210/240| |Unitary A/C|Water cooled split system|8.3_IPLV_ at 75°F Ent. Water|8.3_IPLV_ at 75°F Ent. Water| |Unitary A/C|Evaporatively cooled split system|9.3_EER_ at 95°F Out. Amb.|9.3_EER_ at 95°F Out. Amb.| |Unitary A/C|Evaporatively cooled split system|8.5_IPLV_ at 80°F Out. Amb.|8.5_IPLV_ at 80°F Out. Amb.|
For SI units: °C = (°F-32)/1.8
- Performance for electrically powered equipment with capacity less than 65 000 Btu/h (19 kW) where rated in accordance with ARI 325.
2025 CALIFORNIA MECHANICAL CODE 417
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APPENDIX E
E 502.10.3 Humidity Control. Where additional energy-consuming equipment is provided for adding moisture to maintain specific selected relative humidities in spaces or zones, a humidistat shall be provided. This device shall be capable of being set to prevent energy from being used to produce relative humidity within the space above 30 percent. [ASHRAE 90.2-2007:6.10.3.1] E 502.10.3.1 Cooling. Where additional energyconsuming equipment is provided for reducing humidity, it shall be equipped with controls capable of being set to prevent energy from being used to produce a relative humidity within the space below 50 percent during periods of human occupancy and below 60 percent during unoccupied periods.
[ASHRAE 90.2-2007:6.10.3.2] E 502.10.4 Freeze Protection Systems and Snow/Ice Melting. Freeze protection systems, such as heat tracing of outdoor piping and heat exchangers, including self-regulating heat tracing, shall include automatic controls capable of and configured to shut off the systems where outdoor air temperatures are above 40°F (4°C) or where the conditions of the protected fluid will prevent freezing. Snow- and ice-melting systems shall include automatic controls capable of and configured to shut off the systems where the pavement temperature is above 50°F (10°C) and no precipitation is falling and an automatic or manual control that will allow shutoff where the outdoor temperature is above 40°F (4°C) so that the potential for snow or ice accumulation is negligible.
CRC § 402.1 Medium relevance — show source text
Table 4-B Filter Efficiencies for Central
Ventilation and Air-Conditioning Systems In General Acute Care Hospitals, Outpatient Facilities,
Licensed Clinics and Acute
Psychiatric Hospitals . . . . . . . . . . . 91
Table 4-C Filter Efficiencies for Central
Ventilation and Air-Conditioning Systems In Skilled Nursing Facilities, Intermediate Care
Facilities and Correctional
Treatment Centers . . . . . . . . . . . . . 91
Table 402.1 Minimum Ventilation Rates in
Breathing Zone . . . . . . . . . . . . . . . . 92
Table 403.2.2 Zone Air Distribution Effectiveness. . 95
Table 403.7 Minimum Exhaust Rates. . . . . . . . . 96
CHAPTER 5 EXHAUST SYSTEMS . . . . . . . . . . 97
501.0 General. . . . . . . . . . . . . . . . . . . . . . 99
501.1 Applicability. . . . . . . . . . . . . . . . . . . 99
502.0 Termination. . . . . . . . . . . . . . . . . . . 99
502.1 Exhaust Opening Protection. . . . . . 99
502.2 Termination of Exhaust Ducts . . . . 99
2025 CALIFORNIA MECHANICAL CODE
Part I Environmental Air Ducts and
Product-Conveying Systems . . . . 99
503.0 Motors, Fans, and Filters . . . . . . . . 99
503.1 General. . . . . . . . . . . . . . . . . . . . . . 99
503.2 Fans . . . . . . . . . . . . . . . . . . . . . . . . 99
504.0 Environmental Air Ducts . . . . . . . . . 99
504.1 General. . . . . . . . . . . . . . . . . . . . . . 99
504.2 Independent Exhaust Systems. . . 100
504.3 Domestic Cooking Exhaust Equipment . . . . . . . . . . . . . . . . . . 100
504.4 Clothes Dryers . . . . . . . . . . . . . . . 100
504.5 Heat Recovery Ventilation (HRV) and Energy Recovery Ventilation (ERV) Systems . . . . . . 101
505.0 Product-Conveying Systems . . . . 101
505.1 General. . . . . . . . . . . . . . . . . . . . . 101
505.2 Incompatible Materials . . . . . . . . . 102
505.3 Flammability Limit. . . . . . . . . . . . . 102
505.4 Air-Moving Devices. . . . . . . . . . . . 102
505.5 Generating Flames, Sparks, or Hot Materials . . . . . . . . . . . . . . 102
505.6 Fire Dampers . . . . . . . . . . . . . . . . 102
505.7 Fire Detection, Smoke Control and Alarm Systems . . . . . . . . . . . . 102
CRC § 402.1 Medium relevance — show source text
TABLE OF CONTENTS
415.1 Air Distribution . . . . . . . . . . . . . . . . 82
416.0 Alarms – Airborne Infection
Isolation Rooms and Protective
Environment Rooms . . . . . . . . . . . . 82
417.0 Testing and Balancing Airborne
Infection Isolation Rooms and
Protective Environment Rooms . . . 82
418.0 Design Requirements for Ethylene Oxide (ETO) Sterilization Areas. . . . . . . . . . . . . . 82
418.1 Air Changes . . . . . . . . . . . . . . . . . . 82
418.2 Exhaust Requirements . . . . . . . . . . 82
418.3 Ventilation Requirements . . . . . . . . 82
418.4 Gas Valves . . . . . . . . . . . . . . . . . . . 82
418.5 Alarm Systems . . . . . . . . . . . . . . . . 83
419.0 Neonatal Intensive Care Units . . . . 83
419.1 Formula Preparation Area . . . . . . . 83
419.2 Treatment Area/Room . . . . . . . . . . 83
Table 4-A Pressure Relationship and Ventilation Requirements
for General Acute Care
Hospitals, Skilled Nursing Facilities, Intermediate Care Facilities, Outpatient Facilities, Licensed Clinics, Correctional Treatment Centers, and Acute Psychiatric Hospitals . . . . . . . . . . . 84
Table 4-B Filter Efficiencies for Central
Ventilation and Air-Conditioning Systems In General Acute Care Hospitals, Outpatient Facilities,
Licensed Clinics and Acute
Psychiatric Hospitals . . . . . . . . . . . 91
Table 4-C Filter Efficiencies for Central
Ventilation and Air-Conditioning Systems In Skilled Nursing Facilities, Intermediate Care
Facilities and Correctional
Treatment Centers . . . . . . . . . . . . . 91
Table 402.1 Minimum Ventilation Rates in
Breathing Zone . . . . . . . . . . . . . . . . 92
Table 403.2.2 Zone Air Distribution Effectiveness. . 95
Table 403.7 Minimum Exhaust Rates. . . . . . . . . 96
CHAPTER 5 EXHAUST SYSTEMS . . . . . . . . . . 97
501.0 General. . . . . . . . . . . . . . . . . . . . . . 99
501.1 Applicability. . . . . . . . . . . . . . . . . . . 99
502.0 Termination. . . . . . . . . . . . . . . . . . . 99
502.1 Exhaust Opening Protection. . . . . . 99
502.2 Termination of Exhaust Ducts . . . . 99
2025 CALIFORNIA MECHANICAL CODE
CRC § 303.10.1 Medium relevance — show source text
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
TABLE OF CONTENTS
323.0 Mechanical Equipment
Schedules . . . . . . . . . . . . . . . . . . . 62
324.0 Diesel-Powered Emergency
Generators . . . . . . . . . . . . . . . . . . . 62
325.0 Alternate Source of Power for
Safe Temperatures. . . . . . . . . . . . . 62
Table 303.10.1 Reduction of Clearances with
Specified Forms of Protection . . . . 63
Table 313.3 Hangers and Supports . . . . . . . . . . 65
CHAPTER 4 VENTILATION AIR . . . . . . . . . . . . 67
401.0 General. . . . . . . . . . . . . . . . . . . . . . 69
401.1 Applicability. . . . . . . . . . . . . . . . . . . 69
401.2 Indoor Swimming Pools . . . . . . . . . 69
401.3 Filters . . . . . . . . . . . . . . . . . . . . . . . 69
402.0 Ventilation Air . . . . . . . . . . . . . . . . . 69
402.1 Occupiable Spaces. . . . . . . . . . . . . 69
402.2 Natural Ventilation Procedure. . . . . 70
Table Minimum Openable Areas:
402.2.1.6(A)(1) Single Openings . . . . . . . . . . . . . . . 71
Table Minimum Openable Areas:
402.2.1.6(A)(2) Two Vertically
Spaced Openings . . . . . . . . . . . . . . 71
402.3 Mechanical Ventilation . . . . . . . . . . 71
402.4 Outdoor Air Intakes. . . . . . . . . . . . . 71
Table 402.4.1 Air Intake Minimum
Separation Distance . . . . . . . . . . . . 72
403.0 Ventilation Rates . . . . . . . . . . . . . . 72
403.1 General. . . . . . . . . . . . . . . . . . . . . . 72
403.2 Zone Calculations. . . . . . . . . . . . . . 73
403.3 Single-Zone Systems . . . . . . . . . . . 73
403.4 One Hundred Percent Outdoor
Air Systems . . . . . . . . . . . . . . . . . . 73
403.5 Multiple-Zone Recirculating Systems . . . . . . . . . . . . . . . . . . . . . 73
403.6 Design for Varying Operating Conditions. . . . . . . . . . . . . . . . . . . . 74
403.7 Exhaust Ventilation. . . . . . . . . . . . . 74
403.8 Dynamic Reset . . . . . . . . . . . . . . . . 75
403.9 Air Classification and
CRC § 403.7 Medium relevance — show source text
1
Table 403.7_Notes 11 & 12_
||||X|X||||||||||||||||||||This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.
2025 CALIFORNIA MECHANICAL CODE 67
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68 2025 CALIFORNIA MECHANICAL CODE
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CHAPTER 4
VENTILATION AIR
401.0 General.
401.1 Applicability. This chapter contains requirements for ventilation air supply, exhaust, and makeup air requirements for occupiable spaces within a building. [OSHPD 1, 1R, 2, 3, 4 & 5] See Sections 406.0 through 419.0. [SFM] Air filters shall comply with all requirements of Part 12, Title 24, Chap- ter 12-71, SFM Standard 12-71-1. Spaces within buildings, except those within a dwelling unit in residential occupancies where occupants are nontransient, shall comply with Section 402.0 through Section 404.0. Requirements for ventilation air rate for dwelling units in residential occupancies, where the occupants are nontransient, shall be in accordance with Section 405.0 or ASHRAE 62.2.
401.2 Indoor Swimming Pools. The design of ventilation systems serving an indoor aquatic facility (natatorium) shall comply with the Uniform Swimming Pool, Spa and Hot Tub Code (USPSHTC).
401.3 Filters. [BSC-CG & DSA-SS] In mechanically ven- tilated buildings, provide regularly occupied areas of the building with air filtration media for outside and return air that provides at least a Minimum Efficiency Reporting Value (MERV) of 13. MERV 13 filters shall be installed prior to occupancy, and recommendations for maintenance with fil- ters of the same value shall be included in the operation and maintenance manual in compliance with Chapter 5, Division 5.5 of the California Green Building Standards Code (CAL- Green).
Exception: Existing mechanical equipment.
401.3.1 Labeling. Installed filters shall be clearly labeled by the manufacturer indicating the MERV rating.
402.0 Ventilation Air.
402.1 Occupiable Spaces. Occupiable spaces listed in Table 402.1 shall be designed to have ventilation (outdoor) air for occupants in accordance with this chapter. [DSA-SS] Ven- tilation air requirements for occupancies regulated by the California Energy Commission are found in the California Energy Code.
[CEC] Ventilation air requirements for occupancies regu- lated by the California Energy Commission and found in the California Energy Code supersede those of the California Mechanical Code.
CRC § 416.2 Medium relevance — show source text
0_
414.0
415.0
416.0 – 416.2
416.3
416.4
417.0
418.0
419.0
Table 4-A
Table 4-B
Table 4-C
Table 402.1
Table 403.7_Notes 11 & 12_
|X|||||||X||||||||||||||||| |Adopting Agency
Adopt Entire Chapter
Adopt Entire Chapter as
amended (amended sections
listed below)
Adopt only those sections
that are listed below
Chapter/Section
401.1
401.3
401.3.1
402.1
402.1.2
402.2
402.3
403.0
403.7.2.1 – 403.7.2.4
405.3
406.0
407.0
408.0
409.0
410.0
411.0
412.0
413.0
414.0
415.0
416.0 – 416.2
416.3
416.4
417.0
418.0
419.0
Table 4-A
Table 4-B
Table 4-C
Table 402.1
Table 403.7_Notes 11 & 12_
||||X|X||||||||||||||||||||This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.
2025 CALIFORNIA MECHANICAL CODE 67
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68 2025 CALIFORNIA MECHANICAL CODE
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CHAPTER 4
VENTILATION AIR
401.0 General.
401.1 Applicability. This chapter contains requirements for ventilation air supply, exhaust, and makeup air requirements for occupiable spaces within a building. [OSHPD 1, 1R, 2, 3, 4 & 5] See Sections 406.0 through 419.0. [SFM] Air filters shall comply with all requirements of Part 12, Title 24, Chap- ter 12-71, SFM Standard 12-71-1. Spaces within buildings, except those within a dwelling unit in residential occupancies where occupants are nontransient, shall comply with Section 402.0 through Section 404.0. Requirements for ventilation air rate for dwelling units in residential occupancies, where the occupants are nontransient, shall be in accordance with Section 405.0 or ASHRAE 62.2.
CRC § 62.1 Medium relevance — show source text
(c) Any higher rate that can be demonstrated, to the satisfaction of the Authority Having Jurisdiction, to reduce overall system annual energy use by offsetting reheat/recool energy losses through a reduction in outdoor air intake for the system.
(d) The airflow rate required to be in accordance with applicable codes or accreditation standards, such as pressure relationships or minimum air change rates.
(2) Zones with DDC that comply with the following:
(a) The airflow rate in dead band between heating and cooling does not exceed the larger of the following:
(i) The minimum primary airflow rate required to meet the Simplified Procedure ventilation requirements of Chapter 4 or ASHRAE 62.1 for the zone, permitted to be the average airflow rate as allowed by Chapter 4 or ASHRAE 62.1.
(ii) A higher rate that can be demonstrated, to the satisfaction of the Authority Having Jurisdiction, to reduce overall system annual energy use by offsetting reheat/recool energy losses through a reduction in outdoor air intake.
(iii) The airflow rate required with applicable codes or accreditation standards, such as pressure relationships or minimum air change rates.
(b) The airflow rate that is reheated, recooled, or mixed shall be less than 50 percent of the zone design peak supply rate.
(c) The first stage of heating consists of modulating the zone supply air temperature set
TABLE E 503.5.3
DX COOLING STAGE REQUIREMENTS FOR
MODULATING AIRFLOW UNITS
[ASHRAE 90.1: TABLE 6.5.1.3]
RATING CAPACITY,
Btu/hMINIMUM NUMBER
OF MECHANICAL
COOLING STAGESMINIMUM
COMPRESSOR
DISPLACEMENT*
≥65 000 and <240 0003 ≤35% of full load
≥240 0004 ≤25% full load For SI units: 1000 British thermal units = 0.293 kW
- For mechanical cooling stage control that does not use variable compressor displacement the percent displacement shall be equivalent to the mechanical cooling capacity reduction evaluated at the full load rating conditions for the compressor.
E 503.5.4 Economizer Heating System Impact. HVAC system design and economizer controls shall be such that economizer operation does not increase the building heating energy use during normal operation.
Exception: Economizers on variable air valve (VAV) systems that cause zone level heating to increase due to a reduction in supply air temperature. [ASHRAE 90.1:6.5.1.4] E 503.5.4.1 Economizer Humidification Sys- tem Impact. Systems with hydronic cooling and humidification systems designed to maintain inside humidity at a dew-point temperature more than 35°F (2°C) shall use a fluid economizer where an economizer is required in accordance with Section E 503.5 through Section E 503.5.4.1. [ASHRAE 90.1:6.5.1.5] E 503.5.5 Simultaneous Heating and Cooling Limitation, Zone Controls. Zone thermostatic controls shall prevent the following:
(1) Reheating.
(2) Recooling.
(3) Mixing or simultaneously supplying air that has been previously mechanically heated and air that has
CRC § 401.2 Medium relevance — show source text
401.2 Indoor Swimming Pools. The design of ventilation systems serving an indoor aquatic facility (natatorium) shall comply with the Uniform Swimming Pool, Spa and Hot Tub Code (USPSHTC).
401.3 Filters. [BSC-CG & DSA-SS] In mechanically ven- tilated buildings, provide regularly occupied areas of the building with air filtration media for outside and return air that provides at least a Minimum Efficiency Reporting Value (MERV) of 13. MERV 13 filters shall be installed prior to occupancy, and recommendations for maintenance with fil- ters of the same value shall be included in the operation and maintenance manual in compliance with Chapter 5, Division 5.5 of the California Green Building Standards Code (CAL- Green).
Exception: Existing mechanical equipment.
401.3.1 Labeling. Installed filters shall be clearly labeled by the manufacturer indicating the MERV rating.
402.0 Ventilation Air.
402.1 Occupiable Spaces. Occupiable spaces listed in Table 402.1 shall be designed to have ventilation (outdoor) air for occupants in accordance with this chapter. [DSA-SS] Ven- tilation air requirements for occupancies regulated by the California Energy Commission are found in the California Energy Code.
[CEC] Ventilation air requirements for occupancies regu- lated by the California Energy Commission and found in the California Energy Code supersede those of the California Mechanical Code.
[OSHPD 1, 2, 3, 4 & 5] Health care spaces shall meet the ventilation requirements found in Table 4-A. Ventilation rates for areas not specified in Table 4-A shall have minimum ven- tilation and air change rates per ANSI/ASHRAE Standard 62.1. Where areas with prescribed ventilation rates in both Standards 62.1 and Table 4-A exist, the higher of the two air change rates shall be used.
402.1.1 Construction Documents. The outdoor air ventilation rate and air distribution assumptions made in the design of the ventilation system shall be clearly identified on the construction documents.
402.1.2 Ventilation in Health Care Facilities.
Mechanical ventilation for health care facilities shall be designed and installed in accordance with this code, ASHRAE/ASHE 170, and NFPA 99. [OSHPD 1, 1R, 2, 3, 4 & 5] Ventilation for health care facilities shall be designed and installed in accordance with this code and Table 4-A. All supply-air, return air, and exhaust-air sys- tems shall comply with this code and ASHRAE 170. When the requirements of this code conflict with ASHRAE 170, the most restrictive requirements shall prevail. The text of ASHRAE 170 shall be modified as follows:
(1) ASHRAE 170. Section 6.1.2.1 -- Also see Section 319.0.
(2) ASHRAE 170. Section 6.3.1.3 – Modify as follows: Relief air other than class 1 shall discharge at least 10 feet (3048 mm) from any outside air intake.
CRC § 8.2 Medium relevance — show source text
2 ft**|Hvs ≤ 8.2 ft|8.2 ft <****Hvs ≤ 16.4 ft|8.2 ft <****Hvs ≤ 16.4 ft|16.4 ft <****Hvs|16.4 ft <****Hvs| |Vbz/Az ≤
(CFM/ft2)|As/Al
≤ 0.5|As/Al
> 0.5|As/Al
≤ 0.5|As/Al
> 0.5|As/Al
≤ 0.5|As/Al
> 0.5| |0.2|2.0|1.3|1.3|0.8|0.9|0.6| |0.4|4.0|2.6|2.5|1.6|1.8|1.2| |0.6|6.0|3.9|3.8|2.5|2.7|1.7| |0.8|8.0|5.2|5.0|3.3|3.6|2.3| |1.1|11.0|7.1|6.9|4.5|4.9|3.2|For SI unit: 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute per square foot = 5.08 [(L/s)/m [2] ], 1 square foot = 0.0929 m [2], 1 foot = 304.8 mm,
Where:
Vbz = breathing zone outdoor airflow, per Table 402.1. Az = zone floor area, the net occupiable floor area of the ventilation zone. Hvs = vertical separation between the center of the top and bottom openings’ free operable area; in case of multiple horizontally spaced pairs of openings, use shortest distance encountered. As = openable area of smallest opening (top or bottom); in case of multiple horizontally spaced pairs of top-and-bottom openings, use aggregated areas. Al = openable area of largest opening (top or bottom); in case of multiple horizontally spaced pairs of top-and-bottom openings, use aggregated areas.
Volumetric airflow rates used to estimate required operable area are based on the following:
Dry-air density of 0.075 lbda/ft [3] (1.2 kgda/m [3] ) at a barometric pressure of 1 atm (101.3 kPa) and an air temperature of 70°F (21°C)
Temperature difference between indoors and outdoors of 1.8°F (1°C)
Gravity constant of 32.2 ft/s [2] (9.81m/s [2] )
Window discharge coefficient of 0.6
ical ventilation systems shall include controls, manual or automatic, that enable the fan system to operate wherever the spaces served are occupied. The system shall be designed to maintain minimum outdoor airflow as required by Section 403.0 under any load conditions.
CRC § 303.10.1 Medium relevance — show source text
318.1 Applicability . . . . . . . . . . . . . . . . . . 60
318.2 Services/Systems and Utilities . . . . 60
319.0 Steam and Hot-Water Systems . . . 60
319.1 Requirements for Hospitals and Optional Services Provided in Correctional Treatment Centers . . . 60
319.2 Requirements for Skilled Nursing, Intermediate Care Facilities and Basic Services
Provided in Correctional
Treatment Centers . . . . . . . . . . . . . 61
320.0 Air Conditioning and Heating Systems . . . . . . . . . . . . . . 61
320.1 Requirements for Hospitals and Optional Services Provided in Correctional Treatment Centers . . . 61
320.2 Requirements for Skilled Nursing, Intermediate Care Facilities and Basic Services
Provided in Correctional
Treatment Centers . . . . . . . . . . . . . 61
320.3 Requirements for Outpatient Facilities and Licensed Clinics. . . . 61
320.4 Telephone and Technology Equipment Centers. . . . . . . . . . . . . 61
320.5 Psychiatric Services. . . . . . . . . . . . 61
321.0 Essential Mechanical Provisions . . . 61
322.0 Sensitive Areas or Rooms . . . . . . . 62
xxix
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
TABLE OF CONTENTS
323.0 Mechanical Equipment
Schedules . . . . . . . . . . . . . . . . . . . 62
324.0 Diesel-Powered Emergency
Generators . . . . . . . . . . . . . . . . . . . 62
325.0 Alternate Source of Power for
Safe Temperatures. . . . . . . . . . . . . 62
Table 303.10.1 Reduction of Clearances with
Specified Forms of Protection . . . . 63
Table 313.3 Hangers and Supports . . . . . . . . . . 65
CHAPTER 4 VENTILATION AIR . . . . . . . . . . . . 67
401.0 General. . . . . . . . . . . . . . . . . . . . . . 69
401.1 Applicability. . . . . . . . . . . . . . . . . . . 69
401.2 Indoor Swimming Pools . . . . . . . . . 69
401.3 Filters . . . . . . . . . . . . . . . . . . . . . . . 69
402.0 Ventilation Air . . . . . . . . . . . . . . . . . 69
402.1 Occupiable Spaces. . . . . . . . . . . . . 69
402.2 Natural Ventilation Procedure. . . . . 70
Table Minimum Openable Areas:
Frequently asked questions
Do I always use Table 402.1 rates for a house?
No. Dwelling units are covered separately; see § 401.1 and § 405.0 — the code points residential dwelling ventilation toward ASHRAE 62.2 or § 405.0 rather than Table 402.1.
What if my space is regulated by the Energy Code?
If the occupancy is regulated by the California Energy Commission, the Energy Code provisions (e.g., Section 120.1 / 150.0 methods) may supersede CMC Chapter 4 — check § 402.1 and the California Energy Code.
How do I calculate zone ventilation for multiple rooms?
Use the breathing‑zone equation in § 403.2.1 (Vbz = Rp·Pz + Ra·Az) for each ventilation zone, then combine per § 403.0–403.2.
Are natural ventilation (windows) options allowed?
Yes — the code contains a Natural Ventilation Procedure (Section 402.2) with minimum openable area tables and controls; natural ventilation is an alternate path but has specific requirements.
Do I need to show ventilation rates on the drawings?
Yes. § 402.1.1 requires the outdoor air rate and distribution assumptions to be clearly identified on construction documents.
Is filtration specified anywhere?
Yes — mechanically ventilated, regularly occupied areas are directed to have at least MERV‑13 filtration per § 401.3 (with limited exceptions).
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