CMC · California Mechanical Code
Ventilation rates and calculation procedures
This hub explains where to find CMC requirements and equations for outdoor‑air rates, intake siting, and system ventilation efficiency (see §§402.4, 403.3, 403.5 and Appendix G) .
Last reviewed: July 6, 2026
Overview
This section of the California Mechanical Code (CMC) sets the required outdoor‑air and exhaust rates for occupied spaces and prescribes the calculation methods to size intakes, ducts and fans. It covers natural and mechanical ventilation, intake siting, breathing‑zone rates and the equations for single‑zone, 100% outdoor‑air and multiple‑zone recirculating systems, including simplified and alternate procedures for system ventilation efficiency. See §402.4 for outdoor‑air intake siting and separation distances and Table 402.4.1 for minimum separation distances .
Core calculation procedures are in Chapter 4: single‑zone systems use Equation §403.3, 100% outdoor‑air systems use Equation §403.4, and multiple‑zone recirculating systems follow §403.5 with uncorrected outdoor‑air and efficiency methods (Equations 403.5.1 and 403.5.2) to determine Vot . The code also references ASHRAE methods (62.1/62.2) for zone breathing‑zone rates, controls and special procedures; Appendix G provides an example outdoor‑air calculation to illustrate the steps in practice .
Keep these sections handy when preparing design documents and ventilation schedules: they tell you which equations, tables and referenced standards to use to show compliance and how to size intakes, specify controls and verify as‑installed airflows. The code integrates ASHRAE procedures for rates and verification, so expect cross‑references to ASHRAE 62.1 and 62.2 throughout the ventilation chapters .
In this section
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 62.2 High relevance — show source text
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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where:
Q 50 = leakage rate at 50 Pa. V du = dwelling unit conditioned volume, ft [3] . ACH 50 = air changes per hour at 50 Pa (0.2 inch water). 2. If dwelling unit envelope leakage less than 2 ACH 50 is confirmed by field verification and diagnostic testing, Q 50 shall be calculated according to Equation 150.0-D below, using the value for dwelling unit envelope leakage less than 2 ACH 50 verified by the procedures specified in Reference Residential Appendix RA3.8. (Equation 150.0-D) Q 50 = V du x Verified ACH 50 /60 min
where:
Q 50 = leakage rate at 50 Pa. V du = dwelling unit conditioned volume, ft [3] . ACH 50 = air changes per hour at 50 Pa (0.2 inch water). b. The Effective Annual Average Infiltration Rate ( Q inf ) shall be calculated using Equation 150.0-E [ASHRAE 62.2:4.1.2.1]. (Equation 150.0-E) Q inf = 0.052 × Q 50 × wsf × [ H/H r ] [z]
where:
CMC § 402.1. High relevance — show source text
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.
402.4 Outdoor Air Intakes. Ventilation system outdoor air intakes shall be designed in accordance with Section 402.4.1 through Section 402.4.5. [ASHRAE 62.1:5.5]
402.4.1 Location. Outdoor air intakes (including openings that are required as part of a natural ventilation system) shall be located such that the shortest distance from the intake to any specific potential outdoor contaminant source listed in Table 402.4.1 shall be equal to or greater than the following:
(1) The separation distance in Table 402.4.1 or
(2) The calculation methods in ASHRAE 62.1 Normative Appendix B and shall comply with all other requirements of this section. [ASHRAE 62.1:5.5.1]
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VENTILATION AIR
TABLE 402.4.1
AIR INTAKE MINIMUM SEPARATION DISTANCE
[ASHRAE 62.1:TABLE 5-1]
OBJECT MINIMUM
DISTANCE
(feet)
Class 2 air exhaust/relief outlet10
Class 3 air exhaust/relief outlet15
Class 4 air exhaust/relief outlet30
Cooling tower exhaust25
Cooling tower intake or basin15
Driveway, street, or parking place5
Garage entry, automobile loading area, or drive-in
queue15
Garbage storage/pick-up area,CMC § 150.0 High 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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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 § 403.3 High relevance — show source text
403.3 Single-Zone Systems. For ventilation systems where one or more air handlers supply a mixture of outdoor air and recirculated air to only one ventilation zone, the outdoor air intake flow ( Vot ) shall be determined in accordance with Equation 403.3. [ASHRAE 62.1:6.2.2]
Vot = Voz (Equation 403.3)
403.4 One Hundred Percent Outdoor Air Systems. For ventilation systems where one or more air handlers supply only outdoor air to one or more ventilation zones, the outdoor air intake flow ( Vot ) shall be determined in accordance with Equation 403.4. [ASHRAE 62.1:6.2.3]
Vot = ∑ all zones Voz (Equation 403.4)
403.5 Multiple-Zone Recirculating Systems. For ventilation systems where one or more air handlers supply a mixture of outdoor air and recirculated air to more than one ventilation zone, the outdoor air intake flow ( Vot ) shall be determined in accordance with Section 403.5.1 through Section 403.5.2. [ASHRAE 62.1:6.2.4]
403.5.1 Uncorrected Outdoor Air Intake. The uncorrected outdoor air intake ( Vou ) flow shall be determined in accordance with Equation 403.5.1. [ASHRAE 62.1:6.2.4.1]
(Equation 403.5.1) Vou = D ∑ all zones ( Rp•Pz ) + ∑ all zones ( Ra•Az )
403.5.1.1 Occupant Diversity. The occupant diversity ratio ( D) shall be determined in accordance with Equation 403.5.1.1 to account for variations in population within the ventilation zones served by the system.
(Equation 403.5.1.1) D = Ps / ∑ all zones Pz
Where the system population ( Ps ) is the total population in the area served by the system.
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VENTILATION AIR
Exception: Alternative methods to account for occupant diversity shall be permitted, provided that the resulting ( Vou ) value is not less than that determined in accordance with Equation 403.5.1.
[ASHRAE 62.1:6.2.4.1.1]
403.5.1.2 System Ventilation Efficiency. The system ventilation efficiency ( Ev ) shall be determined in accordance with Section 403.5.1.3 for the
simplified procedure or Section 404.0 for the alternate procedure. These procedures also establish zone minimum primary airflow rates for VAV systems.
[ASHRAE 62.1:6.2.4.2]
403.5.1.3 Simplified Procedure for System Ventilation Efficiency. System ventilation efficiency ( Ev ) shall be determined in accordance with Equation 403.5.1.3(1) or Equation 403.5.1.3(2).
CMC § 403.5.1.1 High relevance — show source text
403.5.1.1 Occupant Diversity. The occupant diversity ratio ( D) shall be determined in accordance with Equation 403.5.1.1 to account for variations in population within the ventilation zones served by the system.
(Equation 403.5.1.1) D = Ps / ∑ all zones Pz
Where the system population ( Ps ) is the total population in the area served by the system.
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VENTILATION AIR
Exception: Alternative methods to account for occupant diversity shall be permitted, provided that the resulting ( Vou ) value is not less than that determined in accordance with Equation 403.5.1.
[ASHRAE 62.1:6.2.4.1.1]
403.5.1.2 System Ventilation Efficiency. The system ventilation efficiency ( Ev ) shall be determined in accordance with Section 403.5.1.3 for the
simplified procedure or Section 404.0 for the alternate procedure. These procedures also establish zone minimum primary airflow rates for VAV systems.
[ASHRAE 62.1:6.2.4.2]
403.5.1.3 Simplified Procedure for System Ventilation Efficiency. System ventilation efficiency ( Ev ) shall be determined in accordance with Equation 403.5.1.3(1) or Equation 403.5.1.3(2).
[ASHRAE 62.1:6.2.4.3 – 6.2.4.3.1]
[Equation 403.5.1.3(1)]
Ev = 0.88 • D + 0.22 for D < 0.60
Ev = 0.75 for D ≥ 0.60 [Equation 403.5.1.3(2)]
403.5.1.4 Zone Minimum Primary Airflow. For each zone, the minimum primary airflow ( Vpz-min ) shall be determined in accordance with Equation 403.5.1.4. [ASHRAE 62.1:6.2.4.3.2]
Vpz-min = Voz• 1.5 (Equation 403.5.1.4)
403.5.2 Outdoor Air Intake. The design outdoor air intake flow ( Vot ) shall be determined in accordance with Equation 403.5.2. [ASHRAE 62.1:6.2.4.4]
Vot = Vou / Ev (Equation 403.5.2)
403.6 Design for Varying Operating Conditions. Ventilation systems shall be designed to be capable of providing not less than the minimum ventilation rates required in the breathing zone where the zones served by the system are occupied, including all full- and part-load conditions. The minimum outdoor air intake flow shall be permitted to be less than the design value at part-load conditions. [ASHRAE 62.1:6.2.5 – 6.2.5.1]
CMC § 2025 High relevance — show source text
Appendix B Procedures to be Followed to Place Gas Equipment in Operation. Appendix B provides requirements for the procedures that apply after an appliance is installed in place, piped, and connected to its venting system. The requirements include adjusting the burner input, air adjustments, verifying operation of safety shutoffs, automatic ignition, and protective devices, checking draft for vent-connected appliances, and operating instructions.
Appendix C Installation and Testing of Oil (Liquid) Fuel-Fired Equipment. Appendix C governs the installation, testing, or repair of oil or liquid fuel-burning equipment used in buildings or structures and equipment.
Appendix D Fuel Supply: Manufactured/Mobile Home Parks and Recreational Vehicle Parks. The provisions of this appendix apply to the fuel gas piping systems of mobile home and recreational vehicle parks. These provisions also apply to the use, maintenance, and installation for supplying fuel gas for accessory buildings or structures, and building components.
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FORMAT OF THE UNIFORM MECHANICAL CODE
Appendix E Sustainable Practices. This appendix provides a comprehensive set of technically sound provisions that encourage sustainable practices and works toward improving the design and construction of mechanical systems that result in a positive long-term environmental impact. Environmental sustainability is important because it involves natural resources that human beings need for economic or manufactured capital. Their sustainability is defined by their reliance on infinitely available resources that are naturally occurring, constant, and free to access.
Appendix F Sizing of Venting Systems and Outdoor Combustion and Ventilation Opening Design. Appendix F provides added information on the sizing of gas vents. This appendix is useful to the end user for the proper sizing of venting systems. A series of examples are given that show how to use the tables and other requirements of Chapter 8. In addition, Appendix F shows an example of how to determine the required combination of indoor and outdoor combustion air opening sizes for appliances under Chapter 7. The combustion air example also provides a table that contains the required volume of space per the appliance Btu/h input based on the standard method.
Appendix G Example Calculation of Outdoor Air Rate. Appendix G gives an example of how to calculate the required outdoor air rate under Chapter 4.
Appendix H Professional Qualifications. Appendix H provides a baseline of knowledge for installers, inspectors, or employers working with and around systems covered within the scope of this code to maintain health and safety.
Appendix I Indoor Horticultural Facilities. Appendix I addresses indoor spaces using environmental controls for horticultural cultivation and processing of plants for human ingestion, inhalation, and topical application. The appendix includes recommendations pertaining to fire protection and suppression systems, carbon dioxide detection systems, flammable solvents, ventilation and exhaust systems, particulate and odor control, and fumigation.
Appendix J Clean Air Delivery. Appendix J provides criteria for an increased level of protection for occupant health by delivering and monitoring clean air in occupied areas of certain buildings. This appendix addresses Demand Control Ventilation (DCV) for occupancy groups A, B, E, and I and recommends that each occupiable zone have CO 2 sensors which communicate with building mechanical systems to adjust airflow rates and maintain acceptable CO 2 levels. Additionally, this appendix contains provisions for mechanical system controls pertaining to sensor calibration, intervals for collected data, and automatic remediation actions to increase the amount of outdoor
CMC § 1 Medium relevance — show source text
Appendix G Example Calculation of Outdoor Air Rate. Appendix G gives an example of how to calculate the required outdoor air rate under Chapter 4.
Appendix H Professional Qualifications. Appendix H provides a baseline of knowledge for installers, inspectors, or employers working with and around systems covered within the scope of this code to maintain health and safety.
Appendix I Indoor Horticultural Facilities. Appendix I addresses indoor spaces using environmental controls for horticultural cultivation and processing of plants for human ingestion, inhalation, and topical application. The appendix includes recommendations pertaining to fire protection and suppression systems, carbon dioxide detection systems, flammable solvents, ventilation and exhaust systems, particulate and odor control, and fumigation.
Appendix J Clean Air Delivery. Appendix J provides criteria for an increased level of protection for occupant health by delivering and monitoring clean air in occupied areas of certain buildings. This appendix addresses Demand Control Ventilation (DCV) for occupancy groups A, B, E, and I and recommends that each occupiable zone have CO 2 sensors which communicate with building mechanical systems to adjust airflow rates and maintain acceptable CO 2 levels. Additionally, this appendix contains provisions for mechanical system controls pertaining to sensor calibration, intervals for collected data, and automatic remediation actions to increase the amount of outdoor air provided to each occupiable zone. The CO 2 sensors addressed in this appendix are intended to give notifications that can assist with awareness of unhealthy levels and give insight to building occupants as to when mitigation action is necessary.
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SAMPLE LEGISLATION FOR ADOPTION OF THE UNIFORM MECHANICAL CODE
The Uniform Codes are designed to be adopted by jurisdictions through an ordinance. Jurisdictions wishing to adopt the 2024 Uniform Mechanical Code as an enforceable regulation governing mechanical systems by reference should ensure the legal basis under which adoption and implementation are included in the ordinance.
The following sample ordinance is a guide for drafting an ordinance for adoption that addresses key components regulations and resolutions.
ORDINANCE NO.
An ordinance of the [JURISDICTION] adopting the 2024 edition of the Uniform Mechanical Code, regulating and controlling the design, construction, quality of materials, erection, installation, alteration, repair, location, relocation, replacement, addition to, use or maintenance of mechanical systems in the [JURISDICTION]; providing for the issuance of permits and collection of fees therefor; repealing Ordinance No. of the
[JURISDICTION] and all other ordinances and parts of the ordinances in conflict therewith.
The [GOVERNING BODY] of the [JURISDICTION] does ordain as follows:
Section 1 Codes Adopted by Reference. That certain documents, three (3) copies of which are on file in the office of the [JURISDICTION'S KEEPER OF RECORDS] and the [JURISDICTION], being marked and designated as the 2024 Uniform Mechanical Code, including Appendix Chapters [FILL IN THE APPENDIX CHAPTERS BEING ADOPTED], as published by the International Association of Plumbing and Mechanical Officials, be and is hereby adopted as the Code of the [JURISDICTION], in the State of [STATE NAME] regulating and controlling the design, construction, quality of materials, erection, installation, alteration, repair, location, relocation, replacement, addition to,
CMC § 1.11.0. Medium relevance — show source text
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.
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APPENDIX G
EXAMPLE CALCULATION OF OUTDOOR AIR RATE
The provisions contained in this appendix are not mandatory unless specifically adopted by a state agency, or referenced in the adopting ordinance.
G 101.0 Example Calculation of Outdoor Air Rate.
G 101.1 Example Calculation. Determine the outdoor air rate required for a single zone AC unit serving an interior 2000 square feet (185.81 m [2] ) conference/meeting room with a design occupancy of 100 people. The system supplies and returns air from the ceiling. (See Chapter 4 of this code for guidelines)
Solution:
In accordance with Table 403.2.2, the zone air distribution effectiveness is 1.0 since the system supplies cooling only from the ceiling. Using the rates from Table 402.1 for a conference/meeting room, the minimum system outdoor air rate is calculated to be:
RpPz + RaAz Vot = (Equation G 101.1) Ez
5 x 100 + 0.06 x 2000
= 1.0
= 620 CFM
Where:
Az = zone floor area: the net occupiable floor area of the zone in square feet (m [2] ).
Pz = zone population: The largest number of people expected to occupy the zone during typical usage. Where the number of people expected to occupy the zone fluctuates, Pz shall be permitted to be estimated based on averaging approaches described in Section 403.6.1. Where Pz cannot be accurately predicted during design, it shall be estimated based on the zone floor area and the default occupant density in accordance with Table 402.1. Rp = outdoor airflow rate (CFM) (L/s) required per person in accordance with Table 402.1 .
Ra = outdoor airflow rate required per unit area (CFM/ft [2] )
[(L/s)/m [2] ] in accordance with Table 402.1.
Ez = zone air distribution effectiveness in accordance with Table 403.2.2. 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] ]
RpPz + RaAz Vot = Ez
5 x 100 + 0.06 x 2000
= 1.0
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CMC § 1.0 Medium relevance — show source text
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). b. All dwelling units in a multifamily building shall use the same whole-dwelling unit ventilation system type. The dwelling unit shall comply with Subsections 1 and 2 below.
- Balanced or supply ventilation . A balanced or supply ventilation system shall provide the required whole-dwelling-unit ventilation airflow. Balanced systems with heat recovery or energy recovery that serve a single dwelling unit shall have a fan efficacy of ≤1.0 W/cfm; and
- Compartmentalization testing. The air leakage rate shall not exceed 0.3 cubic feet per minute at 50 Pa (0.2 inch water) per ft [2] of dwelling unit envelope surface area as confirmed by ECC-Rater field verification and diagnostic testing in accordance with the procedures specified in Reference Appendix RA3.8 or NA2.3 as applicable. In multifamily buildings with four or more habitable stories,
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MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS
the field verification and diagnostic testing which requires an ECC-Rater may alternatively be performed by a certified Mechanical Acceptance Test Technician according to the requirements specified in Reference Appendix NA1.9. v. Multifamily building central ventilation system airflow rate tolerance. Multifamily building central ventilation systems that serve multiple dwelling units shall have airflow rates in each dwelling unit served that meet or exceed a design ventilation airflow rate specification. a. Designers shall specify a design ventilation airflow rate for each dwelling unit that is equal to or greater than the rate specified by Equation 160.2-B. b. The design ventilation airflow rate for each dwelling unit shall be stated on the building design plans approved by the enforcement agency. c. Airflow in each dwelling unit shall be no more than 20 percent greater than the specified design ventilation airflow rate. Ventilation systems shall utilize mechanical or software airflow control means to ensure each of the dwelling-unit airflows can be maintained at the design ventilation airflow within this tolerance at all times. System airflow control-means may include but are not limited to constant air regulation devices, orifice plates and variable speed central fans. vi. Local mechanical exhaust. A local mechanical exhaust system shall be installed in each kitchen and bathroom. Systems shall be rated for airflow in accordance with ASHRAE 62.2 Section 7.1. a. Nonenclosed kitchens shall have a demand-controlled mechanical exhaust system meeting the requirements of Section 160.2(b)2Avic. b. Enclosed kitchens and all bathrooms shall have either one of the following options 1 or 2:
- A demand-controlled mechanical exhaust system meeting the requirements of Section 160.2(b)2Avic; or
- A continuous mechanical exhaust system meeting the requirements of Section 160.2(b)2Avid. c. Demand-controlled mechanical exhaust. A local mechanical exhaust system shall be designed to be operated as needed.
- Control and operation. Demand-controlled mechanical exhaust systems shall be provided with at least one of the following controls: A. A readily accessible occupant-controlled ON-OFF control. B. An automatic control that does not impede occupant ON control.
- **Ventilation rate and capture efficiency.
CMC § 140.4 Medium relevance — show source text
b. DOAS cooling coils shall be hydronic cooling coils utilizing space-cooling chilled water loop. ii. Other heating or cooling shall be provided by a heat pump. Electric resistance heating shall not be used. F. Parallel fan-powered boxes used to comply with Section 140.4(a)3Aiii shall use recirculated zone or plenum air shall be used in heating mode. Fans shall cycle on only when there is a demand for heating and shall have a maximum fan power of 0.3 W/cfm at design airflow. Terminal units providing ventilation air shall be set to no greater than the minimum ventilation rate when the zone is in deadband or in heating mode.
(b) Calculations. In making equipment sizing calculations under Subsection (a), all of the following rules shall apply:
- Heating and cooling loads. Heating and cooling system design loads shall be determined in accordance with the procedures described in Subsection A or B below:
A. For systems serving hotel/motel buildings, and nonresidential buildings other than healthcare facilities, the method in the 2017 ASHRAE Handbook, Fundamentals shall be used or as specified in a method approved by the Commission. B. For system serving healthcare facilities the method in the California Mechanical Code shall be used. 2. Indoor design conditions. Indoor design temperature and humidity conditions for comfort applications shall be determined in accordance with Subsection A or B below:
A. For systems serving hotel/motel buildings, and nonresidential buildings other than healthcare facilities, ASHRAE Standard 55 or the 2017 ASHRAE Handbook, Fundamentals Volume, except that winter humidification and summer dehumidification shall not be required. B. For systems serving healthcare facilities the method in the California Mechanical Code shall be used. 3. Outdoor design conditions. Outdoor design conditions shall be selected in accordance with Subsection A or B below: A. For systems serving hotel/motel buildings and nonresidential buildings other than healthcare facilities the design conditions shall meet the following: i. Outdoor design conditions shall be selected from Reference Joint Appendix JA2, which is based on data from the ASHRAE Climatic Data for Region X or the ASHRAE Handbook, Fundamentals Volume. ii. Heating design temperatures shall be no lower than the 99.0 percent Heating Dry Bulb or the Heating Winter Median of Extremes values.
iii. Cooling design temperatures shall be no greater than the 0.5 percent Cooling Dry Bulb and Mean Coincident Wet Bulb values.
B. For system serving healthcare facilities the method in Section 320.0 of the California Mechanical Code shall be used. Exception to Section 140.4(b)3: Cooling design temperatures for cooling towers shall be no greater than the 0.5 percent cooling design wet bulb values. 4. Ventilation. Outdoor air ventilation loads shall be calculated using the ventilation rates required in Section 120.1(c)3. 5. Envelope. Envelope heating and cooling loads shall be calculated using envelope characteristics, including square footage, thermal conductance, Solar Heat Gain Coefficient or shading coefficient, and air leakage, consistent with the proposed design. 6. Lighting. Lighting heating and cooling loads shall be based on actual design lighting levels or power densities as specified in Section 140.6.
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NONRESIDENTIAL AND HOTEL/MOTEL OCCUPANCIES—PERFORMANCE AND PRESCRIPTIVE
CMC § 160.2 Medium relevance — show source text
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.
d. 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 160.2(b)2Aiv. During periods when comfort conditioning is not called for by the space-conditioning thermostat, the CFI ventilation system controls shall operate the space-conditioning system central fan and outdoor air damper(s) when necessary to ensure compliance with the minimum outdoor air ventilation required by Section 160.2(b)2Aiv in accordance with applicable variable mechanical ventilation methods specified in ASHRAE 62.2 Section 4.5.
iii. Air filtration. Air filtration shall conform to the specifications in Section 160.2(b)1. Compliance with ASHRAE 62.2 Sections 6.7 (Minimum Filtration) and 6.7.1 (Filter Pressure Drop) shall not be required. iv. Whole-dwelling unit mechanical ventilation . Multifamily attached dwelling units shall comply with Subsections a and b below.
a. Mechanical ventilation airflow shall be provided at rates greater than or equal to the value determined in accordance with Equation 160.2-B. Total Required Ventilation Rate [ASHRAE 62.2:4.1.1]: (Equation 160.2-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). b. All dwelling units in a multifamily building shall use the same whole-dwelling unit ventilation system type. The dwelling unit shall comply with Subsections 1 and 2 below.
- Balanced or supply ventilation . A balanced or supply ventilation system shall provide the required whole-dwelling-unit ventilation airflow. Balanced systems with heat recovery or energy recovery that serve a single dwelling unit shall have a fan efficacy of ≤1.0 W/cfm; and
- Compartmentalization testing. The air leakage rate shall not exceed 0.3 cubic feet per minute at 50 Pa (0.2 inch water) per ft [2] of dwelling unit envelope surface area as confirmed by ECC-Rater field verification and diagnostic testing in accordance with the procedures specified in Reference Appendix RA3.8 or NA2.3 as applicable. In multifamily buildings with four or more habitable stories,
202 2025 CALIFORNIA ENERGY CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS
the field verification and diagnostic testing which requires an ECC-Rater may alternatively be performed by a certified Mechanical Acceptance Test Technician according to the requirements specified in Reference Appendix NA1.9. v. Multifamily building central ventilation system airflow rate tolerance. Multifamily building central ventilation systems that serve multiple dwelling units shall have airflow rates in each dwelling unit served that meet or exceed a design ventilation airflow rate specification.
CMC § 62.2 Medium relevance — show source text
[ASHRAE 62.2:4.5.1]
E 605.1.7.2 Scheduled Ventilation. This section shall only be used when one or more fixed patterns of designed ventilation are known at the time compliance to Section E 605.0 is being determined. Such patterns include those both clock-driven and driven by typical meteorological data. Compliance with this section shall be demonstrated with either Section E 605.1.7.2.1 or Section E 605.1.7.2.2. [ASHRAE 62.2:4.5.2] E 605.1.7.2.1 Annual Average Schedule. An annual schedule of ventilation complies with this section when the annual average relative exposure is no more than one, and the peak relative exposure shall not exceed five for any time step as calculated in accordance with ASHRAE 62.2. [ASHRAE 62.2:4.5.2.1] E 605.1.7.2.2 Block Scheduling. The schedule of ventilation complies with this section if it is broken into blocks of time and each block individually has an average relative exposure during occupied periods that is no more than one as calculated in ASHRAE 62.2. All blocks shall end with a relative exposure less than or equal to one. [ASHRAE 62.2:4.5.2.2]
E 605.1.7.3 Real-Time Control. A real-time ventilation controller complies with this section when it is designed to adjust the ventilation system based on real-time input to the ventilation calculations so that the average relative exposure during occupied periods is no more than one, and the peak relative exposure shall not exceed five for any time step as calculated in ASHRAE 62.2. The averaging period shall be no more than one year and shall be based on simple, recursive or running average, but not extrapolation.
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E 605.1.3.4(D) Effective Annual Average Infil- tration Rate. Effective Annual Average Infiltration Rate ( Qinf ) shall be calculated using Equation E 605.1.3.4(D):
[Equation E 605.1.3.4(D)]
= [NL] [ • ] [wsf] [ • ] [A][f][loor] Qinf (CFM) 7.3
Where:
NL = normalized leakage wsf = weather and shielding factor from ASHRAE 62.2 Afloor = floor area of residence, ft [2 ]
For SI units: 1 cubic foot per minute = 0.4719 L/s
[ASHRAE 62.2:4.1.2.2] E 605.1.3.5 Different Occupant Density. Table E 605.1.3.1 and Equation E 605.1.3.1 assume two persons in a studio or one-bedroom dwelling unit and an additional person for each additional bedroom. Where higher occupant densities are known, the rate shall be increased by 7.5 ft [3] /min (0.003 m [3] /s) for each additional person. Where approved by the Authority Having Jurisdiction, lower occupant densities shall be permitted to be used. [ASHRAE 62.2:4.1.3] **E 605.1.4 System Type.
Frequently asked questions
How do I calculate the required outdoor‑air intake for a single‑zone VAV or constant‑volume system?
Use Equation §403.3 (Vot = Voz) for single‑zone systems: determine the breathing‑zone outdoor airflow Voz from Table 402.1 (Rp and Ra) and apply the zone air distribution effectiveness from Table 403.2.2; Appendix G includes a worked example you can follow .
Where does the CMC tell me how far an outdoor‑air intake must be from contaminant sources?
Intake siting and minimum separation distances are in §402.4 and Table 402.4.1; the section also permits using ASHRAE 62.1 Appendix B calculation methods where applicable .
Does the CMC accept ASHRAE ventilation methods and when are the simplified vs. alternate procedures used?
Yes — the CMC incorporates ASHRAE 62.1/62.2 methods for rates, procedures and verification. Chapter 4 provides a simplified procedure for system ventilation efficiency (e.g., §403.5.1.3) and an alternate procedure (Chapter 4/Section 404) when more detailed analysis is needed; consult the cited sections for applicability and equations .
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