CMC · California Mechanical Code
What are the required local and general exhaust rates (table lookup)?
Use Table 403.7 to find the minimum exhaust (CFM per unit or per ft²) for each room or occupancy; follow the continuous vs intermittent guidance in the table notes, apply parking‑garage special rules in §403.7, and use §403.8 if you plan dynamic reset of ventilation flows.
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
The California Mechanical Code requires minimum local and general exhaust rates by occupancy category — you determine the required airflow by looking up the space in Table 403.7 and applying the listed CFM per unit or CFM per ft² values. The parking‑garage provisions and related operating rules are set out in § 403.7 and the dynamic reset allowance is in § 403.8. See Table 403.7 for the complete list of minimum exhaust rates and the parking‑garage text in § 403.7 for continuous operation and alternative methods .
The single most important rule: use Table 403.7 to select the minimum exhaust rate for the occupancy (CFM/unit or CFM/ft²); parking garages and special cases are governed by § 403.7 and dynamic reset by § 403.8 .
Requirements in detail
Key defined terms (first mention bolded)
- Local exhaust — exhaust that serves a specific room or source (kitchen hoods, bathroom fans, etc.). See Table 403.7 for values by room type .
- General exhaust — whole‑space or zone exhaust required by occupancy category; values are given as CFM/unit or CFM/ft² in Table 403.7 .
- Dynamic reset — permitted method to vary outdoor air and zone flows with changing conditions (see § 403.8) .
How to use Table 403.7 (step sequence)
- Identify the occupancy category/name that best matches the room (e.g., Bathroom, Residential kitchen, Parking garage) in Table 403.7 .
- Read the required value type: either CFM per unit (a fixed CFM per fixture/room) or CFM per ft² (area‑based). Apply the listed number. Table values are the minimum required exhaust rates .
- Check notes/footnotes in the table for dual values (for example, a continuous vs intermittent rate) and follow the note guidance (lower rate permitted for continuous operation in many cases) .
- For parking garages, follow the special text in § 403.7 (continuous operation, permitted intermittent control, or the alternate 14,000 cfm per operating vehicle approach) .
Representative, decision‑relevant values (condensed)
| Space / decision item | Minimum exhaust (typical unit from Table 403.7) | Decision note / when to use | Code Reference |
|---|---|---|---|
| Bathroom (typical dwelling) | 20 CFM (continuous) or 50 CFM (intermittent) | Use 50 CFM for intermittent/manual operation; 20 CFM allowed for continuous systems | Table 403.7; § 403.7 |
| Residential kitchen (local hood) | 50 CFM / 100 CFM (table shows 50/100) | Table gives lower/higher pair — follow notes for continuous vs intermittent operation | Table 403.7 |
| Toilets — private | 25 / 50 CFM | Dual values; see table notes for single‑occupant vs other uses | Table 403.7 |
| Toilets — public | 50 / 70 CFM | Public toilet rooms list higher rates; use higher where heavy use expected | Table 403.7 |
| Shower rooms | 20 / 50 CFM | Rate per showerhead or per room per table notes | Table 403.7 |
| Parking garages (area‑based) | 0.75 CFM/ft² (example from Table) | Parking garages also have continuous operation requirements and alternative methods in § 403.7 | |
| Parking garages (alternate) | 14,000 CFM per operating vehicle (system capacity method) | Alternate method in § 403.7.2.2 when used in lieu of table rates; determine # operating vehicles per §403.7.2.2 | § 403.7.2.2 |
(These are representative — use the full Table 403.7 to find other occupancies and the exact number to apply.) See Table 403.7 for the full list and the table footnotes for notes 1–11 that affect interpretation .
Exceptions & special cases
- Parking garages: mechanical ventilation systems for enclosed parking garages are required to operate continuously, but exceptions permit automatic intermittent operation triggered by vehicle/occupant detection, or modulation by approved CO/NO₂ sensors; an alternate sizing method (14,000 cfm per operating vehicle) may be used in lieu of Table 403.7 rates — see § 403.7.2 and § 403.7.2.2 .
- Continuous vs intermittent values: many Table 403.7 entries show a lower value permitted for continuous system operation and a higher value for intermittent operation — read the table notes and apply the correct rate per operation mode .
- Open structures: exhaust may not be required where two or more sides of a space are at least 50% open to the outside (table note), so check the note before applying table values .
- Dynamic reset: designers are permitted to use dynamic reset to vary outdoor intake and zone flows as conditions change — this affects how you size controls and could influence how you meet exhaust/makeup balance during part‑load operation; see § 403.8 .
- Recirculation and air class: Table 403.7 assigns an air‑class to many exhaust sources; recirculation of exhaust is governed by air‑classification rules in § 403.9 — exhaust from some spaces must be exhausted to outdoors or meet special cleaning before recirculation is allowed .
If you need to apply the table to a space that is not explicitly listed, the code tells you to use the most similar space in the table or follow Authority Having Jurisdiction guidance (see § 403.9 explanation) .
Common mistakes
- Confusing continuous vs intermittent rates — many table entries show two values; use the lower value only when the system is designed for continuous operation (see table notes) .
- Forgetting parking‑garage special rules — parking garages have both table rates and separate continuous/alternate sizing text in § 403.7; don’t apply only the table without checking § 403.7.2 and its exceptions .
- Recirculating without checking air classification — Table 403.7 assigns Air Class designations; recirculation limits and treatment requirements follow § 403.9 and related notes .
- Applying area rates incorrectly — confirm whether the table gives CFM/unit or CFM/ft² for your occupancy; multiply the area only when a per‑ft² rate is shown in the table .
Worked example — bathroom in a dwelling unit
Scenario: One bathroom (single‑family dwelling) with a mechanical exhaust fan that will operate intermittently (fan switched on when occupied).
- Find the entry: Bathroom in Table 403.7 shows 20/50 under the "EXHAUST RATE (CFM/unit)" column — lower/higher pair corresponds to continuous / intermittent operation (per table notes) .
- Because the fan is intermittent, use the higher value: 50 CFM. Documented required minimum exhaust = 50 CFM to outdoors. Cite: Table 403.7; compliance per § 403.7 .
- If the design used a continuous fan (fan runs during all occupiable hours), the permitted rate would be 20 CFM per Table 403.7 .
- Verify no table notes change the application (e.g., occupant count or fixture count) — for a single bathroom the table unit rate applies directly; for multi‑fixture toilet rooms consult the specific table entries and notes .
Related provisions
- § 403.7 — Exhaust rates for parking garages and operation rules (continuous operation, sensor exceptions, alternate sizing) .
- Table 403.7 — Minimum Exhaust Rates (full occupancy table — CFM/unit, CFM/ft², Air Class) .
- § 403.8 — Dynamic Reset (permitted resetting of outdoor intake and zone airflow rates) .
- § 403.9 — Air classification and recirculation limits (how exhaust/return air can be recirculated depending on air class) .
- Table notes and footnotes associated with Table 403.7 (notes 1–11) — affect interpretation for specific occupancies (continuous vs intermittent, per fixture, per showerhead, open structures, etc.) .
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 402.1 High 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
CMC § 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
CMC § 1.859 Medium relevance — show source text
78|–|1.859|0.463| |35.31|–|2.247|0.559| |38.84|–|2.667|0.663| |42.37|–|3.121|0.775| |45.90|–|3.607|0.895| |49.43|–|4.125|1.022| |52.97|–|–|1.157| |56.50|–|–|1.299| |60.03|–|–|1.449| |63.56|–|–|1.607| |67.09|–|–|1.772| |70.62|–|–|1.944| |81.21|–|–|2.503| |91.81|–|–|3.127| |102.40|–|–|3.813|
For SI units: 1 standard cubic foot per minute = 28.32 SLPM, 1 inch = 25 mm, 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa
Notes: 1 Based on pressure of 14.7 psig (101 kPa) at 68°F (20°C). 2 Based on pressure of 55 psig (379 kPa) at 68°F (20 °C).
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HEALTH CARE FACILITIES AND MEDICAL GAS AND MEDICAL VACUUM SYSTEMS
TABLE 1323.1.4(5) PRESSURE LOSS FOR VACUUM (continued)
FLOW
RATE
(SCFM)1VACUUM LOSS (inch of mercury)
PER 100 FEET FOR COPPER TUBE2Col3 Col4 Col5 Col6 FLOW
RATE
(SCFM)13⁄4 INCH
TUBE1 INCH
TUBE11⁄4 INCH
TUBE11⁄2 INCH
TUBE2 INCH
TUBE49.43 – – – 3.645 0.956 52.97 – – – 4.122 1.081 56.50 – – – 4.626 1.212 63.56 – – – – 1.495 70.62 – – – – 1.803 77.68 – – – – 2.138 84.74 – – – – 2.497 91.81 – – – – 2.882 98.87 – – – – 3.291 105.93 – – – – 3.724 112.99 – – – – 4.181 CMC § 120.1 Medium relevance — show source text
Provide the higher rate where periods of heavy use are expected to occur. The lower rate shall be permitted to be used otherwise.
E – Rate is for a toilet room intended to be occupied by one person at a time. For continuous systems operation during hours of use, the lower rate shall be permitted to be used.
Otherwise the higher rate shall be used.
F – See other applicable standards for exhaust rate.
G – For continuous system operation, the lower rate shall be permitted to be used. Otherwise the higher rate shall be used.
H – Rate is per showerhead.
Notes:
1. For spaces not included in this table, the spaces in Table 120.1-B shall apply.|A – RESERVED.
B – RESERVED.
C – Exhaust shall not be required where two or more sides comprise walls that are at least 50 percent open to the outside.
D – Rate is per water closet, urinal or both. Provide the higher rate where periods of heavy use are expected to occur. The lower rate shall be permitted to be used otherwise.
E – Rate is for a toilet room intended to be occupied by one person at a time. For continuous systems operation during hours of use, the lower rate shall be permitted to be used.
Otherwise the higher rate shall be used.
F – See other applicable standards for exhaust rate.
G – For continuous system operation, the lower rate shall be permitted to be used. Otherwise the higher rate shall be used.
H – Rate is per showerhead.
Notes:
1. For spaces not included in this table, the spaces in Table 120.1-B shall apply.|TABLE 160.2-D—AIRSTREAMS OR SOURCES
[ASHRAE 62.1:TABLE 6-3]Col2 DESCRIPTION AIR CLASS Commercial kitchen grease hoods 4 Commercial kitchen hoods other than grease 3 Hydraulic elevator machine room 2 Refrigerating machinery rooms 3 TABLE 160.2-E—DEMAND-CONTROLLED LOCAL VENTILATION EXHAUST AIRFLOW RATES AND CAPTURE EFFICIENCY Col2 APPLICATION COMPLIANCE CRITERIA Enclosed kitchen or nonenclosed kitchen Vented range hood, including appliance-range hood combinations shall meet either the capture
efficiency (CE) or the airflow rate specified in Table 160.2-G, as applicable.Enclosed kitchen or nonenclosed kitchen Other kitchen exhaust fans, including downdraft: 300 cfm (150 L/s). Bathroom 50 cfm (25 L/s) 210 2025 CALIFORNIA ENERGY CODE
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MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS
TABLE 160.2-F—CONTINUOUS LOCAL VENTILATION EXHAUST AIRFLOW RATES Col2 APPLICATION AIRFLOW Enclosed kitchen 5 ach, based on kitchen volume Bathroom 20 cfm (10 L/s) CMC § 405.4.1 Medium 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.
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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.
CMC § 150.0 Medium relevance — show source text
TABLE 150.0-E—DEMAND-CONTROLLED LOCAL VENTILATION EXHAUST AIRFLOW RATES AND CAPTURE EFFICIENCY Col2 APPLICATION COMPLIANCE CRITERIA Enclosed Kitchen or Nonenclosed Kitchen Vented range hood, including appliance-range hood combinations, shall meet either the
capture efficiency (CE) or the airflow rate specified in Table 150.0-G as applicable.Enclosed Kitchen or Nonenclosed Kitchen Other kitchen exhaust fans, including downdraft: 300 cfm (150 L/s) Bathroom 50 cfm (25 L/s) iv. Continuous mechanical exhaust. A mechanical exhaust system shall be installed to operate continuously. The system may be part of a balanced mechanical ventilation system. a. Control and operation . A manual ON-OFF control shall be provided for each continuous mechanical exhaust system. The system shall be designed to operate during all occupiable hours. The ON-OFF control shall be accessible to the dwelling unit occupant.
b. Ventilation rate. The minimum delivered ventilation shall be at least the amount indicated in Table 150.0-F during each hour of operation.
TABLE 150.0-F—CONTINUOUS LOCAL VENTILATION EXHAUST AIRFLOW RATES Col2 APPLICATION AIRFLOW Enclosed kitchen 5 ACH, based on kitchen volume Bathroom 20 cfm (10 L/s) TABLE 150.0-G—KITCHEN RANGE HOOD AIRFLOW RATES (CFM) AND ASTM E3087 CAPTURE EFFICIENCY (CE)
RATINGS ACCORDING TO DWELLING UNIT FLOOR AREA AND KITCHEN RANGE FUEL TYPECol2 Col3 **DWELLING UNIT FLOOR AREA (ft2) ** HOOD OVER ELECTRIC RANGE HOOD OVER NATURAL GAS RANGE >1500 50% CE or 110 cfm 70% CE or 180 cfm >1000–1500 50% CE or 110 cfm 80% CE or 250 cfm 750–1000 55% CE or 130 cfm 85% CE or 280 cfm <750 65% CE or 160 cfm 85% CE or 280 cfm v. Airflow measurement of local mechanical exhaust by the system installer. The airflow required by Section 150.0(o)1G is the quantity of indoor air exhausted by the ventilation system as installed in the dwelling unit. When a vented range hood utilizes a capture efficiency rating to demonstrate compliance with Section
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SINGLE-FAMILY RESIDENTIAL BUILDINGS— MANDATORY FEATURES AND DEVICES
150.0(o)1Giiib, the airflow listed in the approved directory corresponding to the compliant capture efficiency rating point shall be met by the installed system. The as-installed airflow shall be verified by the system installer to ensure compliance by use of either Subsection a or b below: a. The system installer shall measure the airflow by using a flow hood, flow grid or other airflow measuring device at the mechanical ventilation fan’s inlet terminals/grilles or outlet terminals/grilles in accordance with the procedures in Reference Residential Appendix RA3.7.
CMC § 120.1 Medium relevance — show source text
For spaces not included in this table, the spaces in Table 120.1-B shall apply.|
TABLE 160.2-D—AIRSTREAMS OR SOURCES
[ASHRAE 62.1:TABLE 6-3]Col2 DESCRIPTION AIR CLASS Commercial kitchen grease hoods 4 Commercial kitchen hoods other than grease 3 Hydraulic elevator machine room 2 Refrigerating machinery rooms 3 TABLE 160.2-E—DEMAND-CONTROLLED LOCAL VENTILATION EXHAUST AIRFLOW RATES AND CAPTURE EFFICIENCY Col2 APPLICATION COMPLIANCE CRITERIA Enclosed kitchen or nonenclosed kitchen Vented range hood, including appliance-range hood combinations shall meet either the capture
efficiency (CE) or the airflow rate specified in Table 160.2-G, as applicable.Enclosed kitchen or nonenclosed kitchen Other kitchen exhaust fans, including downdraft: 300 cfm (150 L/s). Bathroom 50 cfm (25 L/s) 210 2025 CALIFORNIA ENERGY CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS
TABLE 160.2-F—CONTINUOUS LOCAL VENTILATION EXHAUST AIRFLOW RATES Col2 APPLICATION AIRFLOW Enclosed kitchen 5 ach, based on kitchen volume Bathroom 20 cfm (10 L/s) TABLE 160.2-G—KITCHEN RANGE HOOD AIRFLOW RATES (cfm) AND ASTM E3087 CAPTURE EFFICIENCY (CE) RATINGS
ACCORDING TO DWELLING UNIT FLOOR AREA AND KITCHEN RANGE FUEL TYPECol2 Col3 **DWELLING UNIT FLOOR AREA (FT2) ** HOOD OVER ELECTRIC RANGE HOOD OVER NATURAL GAS RANGE > 1500 50% CE or 110 cfm 70% CE or 180 cfm > 1000–1500 50% CE or 110 cfm 80% CE or 250 cfm 750–1000 55% CE or 130 cfm 85% CE or 280 cfm < 750 65% CE or 160 cfm 85% CE or 280 cfm TABLE 160.2-H—PRESCRIPTIVE VENTILATION SYSTEM DUCT SIZING [ASHRAE 62.2:TABLE 5-3] Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 Col12 Col13 Col14 Fan airflow rating,
cfm at minimum static
pressuref 0.25 in.CMC § 2.1 Medium 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.
CMC § 0.0929 Medium relevance — show source text
(1) 60 CFM/person for cultivation, production, and processing facilities or factories.
(2) 15 CFM/person for centers and dispensaries.
Ra = outdoor airflow rate required per unit area, 1 CFM/ft [2]
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] ]
Sample Calculation: Determine the outdoor airflow required in the breathing zone ( Vbz ) of an indoor space used for horticultural cultivation with an occupiable floor area of 800 square feet and a maximum of 5 people expected to occupy the zone.
Sample Solution: Vbz = Rp - Pz + Ra - Az Vbz = (60 CFM/person • 5 people) + (1 CFM • 800 SF) Vbz = 1100 CFM. The ventilation system shall be capable of providing not less than 1100 CFM of outdoor air.
I 801.1.2 Ventilation System Requirements. When activated by the gas detection system required by Section I 601.1, the mechanical purge ventilation system shall remain on until manually reset. The purge ventilation system ducting shall terminate outdoors in an approved location. The ventilation system shall be designed to operate at a negative pressure of 0.01 inches water column (0.002 kPa) in relation to the exhausted indoor space.
I 801.1.3 Ventilation for Indoor Cultivation and Storage Spaces. Indoor spaces used for horticultural cultivation and processing and storage shall be provided with ventilation in accordance with Section 402.2. Where
mechanical ventilation is provided, the systems shall be operational when the indoor space(s) are occupied. Air in indoor cultivation and storage spaces shall be classified as Class 2 Air in accordance with Section 403.9.2.
I 801.1.4 Exhaust Ventilation Rate. The exhaust and ventilation system required in this section shall not create a lesser standard of installation than prescribed by the
minimum safety standards adopted by the Authority Having Jurisdiction. Exhaust airflow shall be provided at not less than 0.2 CFM/ft [2] [1.02 (L/s)/m [2] ] of floor area. Exhaust air shall not be used as makeup air, recirculated air, or transfer air. Makeup air shall be provided for more than 150 CFM (70.8 L/s) exhaust. I 801.1.5 Exhaust System Requirements. An exhaust system shall be installed in accordance with Section 505.0 and the following requirements:
(1) Exhaust outlet location(s) in accordance with Section 502.2.3 for product conveying ducts as classified in Section 505.8.
(2) Exhaust air shall terminate directly to the outdoors and shall not be directed onto a public way.
(3) The exhaust inlet shall be not less than 12 inches (305 mm) above the finished floor.
(4) Chemical fume hoods shall be required for flammable solvent processing, shall be listed, and shall be installed in accordance with the manufacturer’s
installation instructions.
(5) Exhaust ducts shall be independent of all other exhaust systems.
(6) The exhaust rate shall be in accordance with the appliable occupancy category as shown in Table 403.7.
CMC § 1.9 Medium relevance — show source text
Natural ventilation shall not be required in kitchens where a local exhaust system is installed in accordance with the California Mechanical Code .
Required ventilation openings shall be permitted to open into a thermally isolated sunroom or roofed porch, deck, or patio where not less than 40 percent of the roofed area perimeter is open to the outdoor air.
Required ventilation openings shall be permitted to open into a thermally isolated sunroom provided there is an openable area between the adjoining room and the sunroom of not less than one-tenth of the floor area of the interior room and not less than 20 square feet (1.9 m [2] ). The minimum openable area of the sunroom to outdoor air shall be based on the total floor area of the adjoining room and the sunroom. 5. The windows, doors, louvers and other approved closeable openings not required by Section R319 may open into a passive solar energy collector for ventilation required by this section. The area of ventilation openings to the outside of the passive solar energy collector shall be increased to compensate for the openings required by the interior space.
R325.1.3 Adjoining rooms. For the purpose of determining light and ventilation requirements, rooms shall be considered to be a portion of an adjoining room where not less than one-half of the area of the common wall is open and unobstructed and provides an opening of not less than one-tenth of the floor area of the interior room and not less than 25 square feet (2.3 m [2] ).
R325.2 Bathrooms. Bathrooms, water closet compartments and other similar rooms shall be provided with aggregate glazing area in windows of not less than 3 square feet (0.3 m [2] ), one-half of which shall be openable.
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.
CMC § 90.1 Medium relevance — show source text
[ASHRAE 90.1: TABLE 6.4.3.4.3]
Col1 OUTDOOR AIR INTAKE (CFM/ft2) Col3 EXHAUST/RELIEF (CFM/ft2) Col5 CLIMATE ZONE NONMOTORIZED1 MOTORIZED NONMOTORIZED3 MOTORIZED 0, 1, 2 0, 1, 2 0, 1, 2 0, 1, 2 0, 1, 2 Any height 20 4 20 4 3 3 3 3 3 Any height 20 10 20 10 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C Fewer than three stories 204 10 20 10 Three or more stories 204 10 204 10 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 Fewer than three stories 204 4 20 4 Three or more stories 204 4 204 4 For SI units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.00047 m [3] /s, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per minute per square foot = 5.08 [(L/s)/m [2] ], 1 inch water gauge = 0.249 kPa
Notes:
1 When tested in accordance with AMCA 500D.
2 Dampers smaller than 12 inches (305 mm) in height, width, or diameter need not be tested but shall be of the same design and construction as the smallest tested damper meeting the listed leakage rate requirement.
3 Nonmotorized dampers smaller than 24 inches (610 mm) in height, width, or diameter shall be permitted to have a leakage rate of 40 CFM/ft 2 [0.203 (m 3 /s)/m 2 ].
4 Where permitted by Section E 503.4.6.4.1, exception 2.
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APPENDIX E
(2) Systems serving zones where humidity levels are required to be maintained with precision of not more than ±5 percent relative humidity to comply with applicable codes or accreditation standards or as approved by the Authority Having Jurisdiction.
[ASHRAE 90.1:6.4.3.6.2]
CMC § 511.3. Medium relevance — show source text
Lower total ach ventilation rates shall be permitted when a hazard assessment, performed as part of an effective laboratory ventilation management plan per AIHA/ASSE Z9.5 3, determines that either (1) acceptable exposure concentrations in the laboratory work area can be achieved with a lower minimum total ach ventilation rate than is listed in Table 4-A or (2) a demand control approach with active sensing of contaminants or appropriate surrogates is used as described in ASHRAE Handbook—HVAC Applications10, Chapter 16, “Laboratories.” g. Examination rooms programmed for use by patients with undiagnosed gastrointestinal symptoms, undiagnosed respiratory symptoms, or undiagnosed skin symptoms. h. A nonrefrigerated body holding room is applicable only to facilities that do not perform autopsies on-site and use the space for short periods while waiting for the body to be transferred. i. Minimum total air changes per hour (ach) shall be that required to provide proper makeup air to kitchen exhaust systems as specified in Section 511.3. Com- mercial cooking areas shall be designed to prevent odors from entering patient spaces. j. Where the “exhaust directly to Outdoors” column is marked yes, all exhaust air shall be discharged directly to the outdoors and not recirculated to other areas. Recirculation room units may be provided where the column is marked yes provided air is not recirculated to other areas. To satisfy exhaust needs, constant replacement air from the outdoors is necessary when the system is in operation. k. The relative humidity (RH) ranges listed are the minimum and/or maximum allowable at any point within the design temperature range required for that space. l. Systems shall be capable of maintaining the rooms within the range during normal operation. Lower or higher temperature shall be permitted when occupants’ comfort and/or medical conditions require those conditions. m. National Institute for Occupational Safety and Health (NIOSH) criteria documents 11 regarding occupational exposure to waste anesthetic gases and vapors and control of occupational exposure to nitrous oxide indicate a need for both local exhaust (scavenging) systems and general ventilation of the areas in which the respective gases are used. ( Informative Note: Refer to NFPA 99 [ 2024 ] for other requirements.) n. If pressure-monitoring device alarms are installed, allowances shall be made to prevent nuisance alarms. Short-term excursions from required pressure relationships shall be allowed while doors are moving or temporarily open. Simple visual methods such as smoke trail, ball-in-tube, or flutterstrip shall be permitted for verification of airflow direction. o. Surgeons or surgical procedures may require room temperatures, ventilation rates, humidity ranges, and/or air distribution methods that exceed the minimum indicated ranges. p. Treatment rooms used for bronchoscopy shall be treated as bronchoscopy rooms. Treatment rooms used for procedures with nitrous oxide shall contain provisions for exhausting anesthetic waste gases. q. In a recirculating ventilation system, HEPA filters shall be permitted instead of exhausting the air from these spaces to the outdoors, provided that the return air passes through the HEPA filters before it is introduced into any other spaces. The entire minimum total air changes per hour of recirculating airflow shall pass through HEPA filters. When these areas are open to larger, nonwaiting spaces, the exhaust air volume shall be calculated based on the seating area of the waiting area. ( Informative Note: The intent here is to not require the volume calculation to include a very large space [e.g., an atrium] just because a waiting area opens onto it.) r. Exhaust rate shall meet or exceed local requirements.
CMC § 1.50 Medium relevance — show source text
|1.50|
For SI units: °C = °F( [5] / 9 ), 1 foot per minute = 0.005 m/s, 1 foot = 304.8 mm
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VENTILATION AIR
TABLE 403.7
MINIMUM EXHAUST RATES
[ASHRAE 62.1: TABLE 6-2]
OCCUPANCY CATEGORY EXHAUST RATE
(CFM/unit)EXHAUST RATE
(CFM/ft2)AIR CLASS Animal Facilities Animal imaging (MRI/CT/PET) – 0.90 3 Animal operating rooms – 3.00 3 Animal postoperative recovery room – 1.50 3 Animal preparation rooms – 1.50 3 Animal procedure room – 2.25 3 Animal surgery scrub – 1.50 3 Large-animal holding room – 2.25 3 Necropsy – 2.25 3 Small-animal-cage room (static cages) – 2.25 3 Small-animal-cage room (ventilated cages) – 1.50 3 Arenas2 – 0.50 1 Art classrooms – 0.70 2 Auto repair rooms1 – 1.50 2 Barber shops – 0.50 2 Bathroom10, 11 20/50 – 2 Beauty and nail salons – 0.60 2 Cells with toilet – 1.00 2 Copy, printing rooms – 0.50 2 Darkrooms – 1.00 2 Educational science laboratories – 1.00 2 Janitor closets, trash rooms, recycling – 1.00 3 Kitchenettes – 0.30 2 Kitchens – commercial – 0.70 2 Locker rooms for athletic, industrial and health care facilities – 0.50 2 All other locker rooms – 0.25 2 Shower rooms7, 9 20/50 – 2 Paint spray booths6 – – 4 Parking garages3 – 0.75 2 Pet shops (animal areas) – 0.90 2 Refrigerating machinery rooms6 – – 3 Residential kitchens7 50/100 – 2 Soiled laundry storage rooms6 – 1.00 3 Storage rooms, chemical6 – 1.50 4 Toilets – private5, 8 25/50 – 2 Toilets – public4, 8 50/70 – 2 Woodwork shop/classrooms – 0.50 2 CMC § 407.1 Medium relevance — show source text
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. Plumbing vents shall be located in relation to out- door air intakes per California Plumbing Code. The bot- tom of outdoor air intakes shall be located as high as practicable, but not less than 10 feet (3048 mm) above ground level. If installed above the roof, they shall be located 18 inches (457 mm) above roof level or 3 feet (914 mm) above a flat roof where heavy snowfall is anticipated. Outside air intakes located in a below grade areaway shall have the top of the areaway extend a minimum of 10 feet (3048 mm) above grade.
Exceptions:
(1) These dimensions may be reduced if it is demon- strated by the submission of details and calculations that location of intakes with respect to exhausts and
their orientation, or the use of special filters, pro- vides equal performance.
(2) The requirements regarding the bottom of outdoor air intakes and installation through the roof do not apply to skilled nursing facilities, intermediate-care facilities or nonsensitive areas in correctional treat-
ment centers.
407.2.2 Exhaust Outlets. Exhaust outlets shall be located a minimum of 10 feet (3048 mm) above adjoining grade and 10 feet (3048 mm) from doors, occupied areas, and operable windows.
Exception: Airborne infection isolation rooms shall comply with Section 414.1.
Frequently asked questions
What if my space is not listed in Table 403.7?
Use the most similar space listed in Table 403.7 or consult the Authority Having Jurisdiction; the code directs air leaving unlisted spaces to be classified like the most similar table entry .
Can I use the lower (continuous) rate if my system cycles off at night?
No — the lower continuous rate is permitted when the system is designed to operate continuously. If the system is intermittent during occupied hours, use the higher (intermittent) rate in the table unless an exception or control strategy specifically permits otherwise .
Are parking garage exhaust systems allowed to be demand‑controlled?
Yes — § 403.7.2 permits intermittent operation if the system is designed to operate automatically on vehicle operation or occupant detection, and allows approved CO/NO₂ sensor modulation per the section’s criteria; otherwise continuous operation is required .
Can exhaust air ever be recirculated?
Recirculation is governed by air classification and § 403.9. Air from some spaces (Class 1) may be recirculated; other classes require exhaust to outdoors or treatment before recirculation — consult § 403.9 and the table’s Air Class column .
Where is dynamic reset allowed and what does it change?
§ 403.8 permits dynamic reset of outdoor intake and zone flows as operating conditions change; this affects control strategies and may change how you size and control makeup/outdoor air components but does not change the Table 403.7 minimum exhaust requirements themselves .
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