Makeup air, air balance and common (master) kitchen ducts

Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:

• CMC § 511.2.3 High relevance — show source text

  511.2.3 Exhaust Fan Operation. A hood exhaust fan(s) shall continue to operate after the extinguishing system has been activated unless fan shutdown is required by a listed component of the ventilation system or by the design of the extinguishing system. The hood exhaust fan shall start upon actuation of the extinguishing system if the exhaust fan and all cooking equipment served by the fan have been shut down, unless fan shutdown is required by a listed component of the ventilation system or by the listing of the extinguishing system. The exhaust fan shall be provided with a means so that the fan is activated when any heat-producing cooking appliance under the hood is turned on. [NFPA 96:8.2.3.1 – 8.2.3.3]

  511.3 Makeup Air. The makeup air quantity shall prevent negative pressures in the commercial cooking area(s) from exceeding 0.02 inch water column (0.005 kPa). Where the fire-extinguishing system activates, makeup air supplied internally to a hood shall be shut off.

  For compensating hoods, where a Type I or Type II hood has an internal discharge of makeup air, the makeup air flow shall not exceed 10 percent of the exhaust airflow, the exhaust airflow shall be the net exhaust from the hood in accordance with Section 508.5.1.2 through Section 508.5.1.5. The total hood exhaust shall be determined in accordance with Equation 511.3.

  E NET = E HOOD – MA ID (Equation 511.3)

  Where:

  E NET = net hood exhaust, CFM (L/s)

  E HOOD = total hood exhaust, CFM (L/s)

  MA ID = makeup air, internal discharge, CFM (L/s)

  For SI units: 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per

  minute = 0.4719 L/s

  511.3.1 Air Balance. Design plans for a facility with a commercial kitchen ventilation system shall include a schedule or diagram indicating the design outdoor air balance. The design outdoor air balance shall indicate the exhaust and replacement air for the facility and the net exfiltration where applicable. The total replacement airflow rate shall equal the total exhaust airflow rate and the net exfiltration.

  511.4 Common Duct (Manifold) Systems. Master kitchen exhaust ducts that serve multiple tenants shall include provision to bleed air from outdoors or from adjacent spaces into the master exhaust duct where required to maintain the necessary minimum air velocity in the master exhaust duct.

  [NFPA 96:8.4.1]

  511.4.1 Connections. Bleed air ducts shall connect to the top or side of the master exhaust duct. [NFPA 96:8.4.2] 511.4.2 Fire Damper. The bleed-air duct shall have a fire damper at least 12 inches (305 mm) from the exhaust duct connection. [NFPA 96:8.4.3]

  511.4.3 Construction and Clearance. The bleed-air

• CMC § 511.3 High relevance — show source text

  E NET = E HOOD – MA ID (Equation 511.3)

  Where:

  E NET = net hood exhaust, CFM (L/s)

  E HOOD = total hood exhaust, CFM (L/s)

  MA ID = makeup air, internal discharge, CFM (L/s)

  For SI units: 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per

  minute = 0.4719 L/s

  511.3.1 Air Balance. Design plans for a facility with a commercial kitchen ventilation system shall include a schedule or diagram indicating the design outdoor air balance. The design outdoor air balance shall indicate the exhaust and replacement air for the facility and the net exfiltration where applicable. The total replacement airflow rate shall equal the total exhaust airflow rate and the net exfiltration.

  511.4 Common Duct (Manifold) Systems. Master kitchen exhaust ducts that serve multiple tenants shall include provision to bleed air from outdoors or from adjacent spaces into the master exhaust duct where required to maintain the necessary minimum air velocity in the master exhaust duct.

  [NFPA 96:8.4.1]

  511.4.1 Connections. Bleed air ducts shall connect to the top or side of the master exhaust duct. [NFPA 96:8.4.2] 511.4.2 Fire Damper. The bleed-air duct shall have a fire damper at least 12 inches (305 mm) from the exhaust duct connection. [NFPA 96:8.4.3]

  511.4.3 Construction and Clearance. The bleed-air

  duct shall have the same construction and clearance requirements as the main exhaust duct from the connection to the exhaust duct to at least 12 inches (305 mm) on both sides of the fire damper. [NFPA 96:8.4.4] 511.4.4 Adjustment. Each bleed air duct shall have a means of adjusting (e.g., by using volume dampers) the bleed air quantity. [NFPA 96:8.4.5] 511.4.5 Adjustment Location. Means to adjust the bleed air quantity shall be installed between the fire damper and the source of bleed air. [NFPA 96:8.4.6]

  511.4.6 Bleed Air Duct. A bleed air duct shall not be used for the exhaust of grease-laden vapors and shall be so labeled. [NFPA 96:8.4.7]

  511.4.7 Disconnect. Unused tenant exhaust connec tions to the master exhaust duct that are not used as bleed

  air connections shall be disconnected and sealed at the main duct. [NFPA 96:8.4.8] 511.5 Solid-Fuel Air Movement Requirements. Where solid-fuel cooking equipment is used, exhaust and replacement air also shall be in accordance with Section 517.0.

  512.0 Auxiliary Equipment.

  512.1 Dampers. Dampers shall not be installed in exhaust ducts or exhaust duct systems. [NFPA 96:9.1.1]

• CMC § 140.9 Medium relevance — show source text

  2. Kitchen ventilation.

  A. Mechanically cooled or heated makeup air delivered to any space with a kitchen hood shall not exceed the greater of: i. The supply flow required to meet the space heating and cooling load; or ii. The hood exhaust flow minus the available transfer air from adjacent spaces. Available transfer air is that portion of outdoor ventilation air serving adjacent spaces not required to satisfy other exhaust needs, such as restrooms, not required to maintain pressurization of adjacent spaces, and that would otherwise be relieved from the building. Exception to Section 140.9(b)2A: Existing kitchen makeup air units not being replaced as part of an addition or alteration.

  142 2025 CALIFORNIA ENERGY CODE

  on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

  NONRESIDENTIAL AND HOTEL/MOTEL OCCUPANCIES—PERFORMANCE AND PRESCRIPTIVE

  COMPLIANCE APPROACHES FOR ACHIEVING ENERGY EFFICIENCY

  B. A kitchen/dining facility having a total Type I and Type II kitchen hood exhaust airflow rate greater than 5,000 cfm shall have one of the following: i. At least 50 percent of all replacement air is transfer air that would otherwise be exhausted; or ii. Demand ventilation system(s) on at least 75 percent of the exhaust air. Such systems shall: a. Include controls necessary to modulate airflow in response to appliance operation and to maintain full capture and containment of smoke, effluent and combustion products during cooking and idle; and b. Include failsafe controls that result in full flow upon cooking sensor failure; and c. Include an adjustable timed override to allow occupants the ability to temporarily override the system to full flow; and d. Be capable of reducing exhaust and replacement air system airflow rates to the larger of: (i) 50 percent of the total design exhaust and replacement air system airflow rates; or (ii) The ventilation rate required as specified by Section 120.1(c)3. iii. Listed energy recovery devices with a sensible heat recovery effectiveness of not less than 40 percent on at least 50 percent of the total exhaust airflow; or iv. A minimum of 75 percent of makeup air volume that is:

  a. Unheated or heated to no more than 60°F; and

  b. Uncooled or cooled without the use of mechanical cooling.

  Exception to Section 140.9(b)2B: Existing hoods not being replaced as part of an addition or alteration. 3. Kitchen exhaust system acceptance. Before an occupancy permit is granted for a commercial kitchen subject to Section 140.9(b), the following equipment and systems shall be certified as meeting the acceptance requirements for code compliance, as specified by the Reference Nonresidential Appendix NA7. A certificate of acceptance shall be submitted to the enforcement agency that certifies that the equipment and systems meet the acceptance requirements specified in NA7.11.

  Exception to Section 140.9(b): Healthcare facilities.

  (c) Prescriptive requirements for laboratory and factory exhaust systems.

  1. Airflow reduction requirements. Building laboratory exhaust systems shall be able to reduce zone exhaust and makeup airflow rates to the occupied and unoccupied minimum exhaust airflow rates based on demand and sensed occupancy as follows:

  A. Occupied minimum exhaust airflow. When occupant sensing controls sense occupants in the space, the minimum exhaust and makeup airflow rates shall be the greater of: i. User-defined airflow not to exceed 1.0 cfm/ft [2] (equivalent to 6 air changes per hour for a 10-foot high ceiling); or ii.

• CMC § 2025 Medium relevance — show source text

  The building’s structural stability is protected by the regulations for cutting and notching of structural members.

  Chapter 4 Ventilation Air. Chapter 4 regulates the minimum requirements for ventilation air supply, exhaust, and makeup air for occupiable spaces within a building. Building ventilation is one important factor affecting the relationship between airborne transmission of respiratory infections and the health and productivity of workers. Ventilation air may be composed of mechanical or natural ventilation, infiltration, recirculated air, transfer air, or a suitable combination of these. Providing a comfortable and healthy indoor environment for building occupants is of primary concern. When determining ventilation rates, typical and unusual significant sources of indoor pollution need to be controlled. Areas such as kitchens, bathrooms, and laundries are all built to allow specific functions. These spaces produce pollutants such as moisture, odors, volatile organic compounds, particles, or combustion byproducts. The purpose of local exhaust is to control concentrates of these pollutants in the room into which they were emitted and to reduce the spread of pollutants into other parts of the occupancy. Local exhaust ventilation is the source control for pollution that is expected in certain rooms. Using local exhaust to extract contaminants before they mix with the indoor environment is essential.

  Chapter 5 Exhaust Systems. Chapter 5 regulates the minimum requirements for exhaust systems. Chapter 5 contains two parts: Part I provides exhaust requirements for environmental air ducts and product conveying systems; Part II provides exhaust requirements for commercial hoods and kitchen ventilation. Environmental air ducts include exhaust ducts used for transporting the air from domestic kitchens, bathrooms, shower rooms, locker rooms, janitor’s closets, and clothes dryers. Systems that carry nonabrasive exhaust, such as smoke, moderate abrasives such as sawdust, and high abrasives such as manganese or acid vapors use product-conveying ducts. Part II provides the minimum fire safety requirements related to the design, installation, inspection, and maintenance of grease-type operations, such as cooking, for both fuel-gas and solid fuel. Cooking produces a significant amount of smoke, fumes, vapors, heat, and other pollutants. Therefore, acceptable kitchen ventilation is necessary to prevent fires from the build-up of grease and to provide the occupants protection from smoke, unpleasant odors, pollutants, and dangerous gases. There are two types of exhaust hoods (Type I and Type II) used in commercial kitchen applications.

  xiv 2025 CALIFORNIA MECHANICAL CODE

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  FORMAT OF THE UNIFORM MECHANICAL CODE

  Type I hoods are intended to be installed above equipment or appliances that generate grease or smoke. Type II hoods are intended to be installed above equipment or appliances that generate steam, vapor, heat, or odors and do not generate grease or smoke.

  Chapter 6 Duct Systems. Chapter 6 regulates requirements for ducts and plenums that are portions of a heating, cooling, ventilation, or exhaust system. This chapter contains material and installation requirements for metal, gypsum, factory-made, flexible, and plastic ducts. It also contains provisions for duct insulation, dampers, fire protection, and automatic shutoff for the building’s air distribution system. It is worth noting that exhaust ducts are regulated by Chapter 5, and combustion air ducts are regulated by Chapter 7.

• California Mechanical Code Medium relevance — show source text

  A mechanical code, as with any other code, is intended to be adopted as a legally enforceable document to safeguard health, safety, property, and public welfare. The code cannot be effective without satisfactory provisions for its administration and enforcement. The Authority Having Jurisdiction is to review the proposed and completed work and decide whether a mechanical system conforms to the code requirements. As a public servant, the Authority Having Jurisdiction enforces the code in an unbiased proper manner. The design professional is responsible for the design of a safe mechanical system. The contractor is responsible for installing the system in accordance with the plans.

  Chapter 2 Definitions. To maintain consistency and encourage the use of common terminology, Chapter 2 establishes definitions to provide clarity of terms and promote the use of a common language throughout the code. Understanding definitions within the context of their application enables greater collaboration, efficiency, standardization, and interpretation in applying and enforcing terms used throughout the code. Codes are technical documents, and every term can impact the meaning of the code text. Terms not defined have a normally accepted meaning.

  Chapter 3 General Regulations. Chapter 3 regulates the general requirements, not specific to other chapters, for installing mechanical systems. Many regulations are not specific mechanical requirements but relate to the overall mechanical system. This chapter contains safety requirements for appliance location and installation, appliance and system access, condensate disposal, clearances to combustibles, and return or outside air used in mechanical systems. Listing method of approval, based on applicable nationally recognized standards for the safe and proper installation of mechanical systems, is essential to ensure protection of public health, safety, and welfare. These safety requirements provide protection for piping, tubing, materials, and structures, including provisions for installation practices addressing stress and strain, sleeving, and hanger support. The building’s structural stability is protected by the regulations for cutting and notching of structural members.

  Chapter 4 Ventilation Air. Chapter 4 regulates the minimum requirements for ventilation air supply, exhaust, and makeup air for occupiable spaces within a building. Building ventilation is one important factor affecting the relationship between airborne transmission of respiratory infections and the health and productivity of workers. Ventilation air may be composed of mechanical or natural ventilation, infiltration, recirculated air, transfer air, or a suitable combination of these. Providing a comfortable and healthy indoor environment for building occupants is of primary concern. When determining ventilation rates, typical and unusual significant sources of indoor pollution need to be controlled. Areas such as kitchens, bathrooms, and laundries are all built to allow specific functions. These spaces produce pollutants such as moisture, odors, volatile organic compounds, particles, or combustion byproducts. The purpose of local exhaust is to control concentrates of these pollutants in the room into which they were emitted and to reduce the spread of pollutants into other parts of the occupancy. Local exhaust ventilation is the source control for pollution that is expected in certain rooms. Using local exhaust to extract contaminants before they mix with the indoor environment is essential.

  Chapter 5 Exhaust Systems. Chapter 5 regulates the minimum requirements for exhaust systems. Chapter 5 contains two parts: Part I provides exhaust requirements for environmental air ducts and product conveying systems; Part II provides exhaust requirements for commercial hoods and kitchen ventilation. Environmental air ducts include exhaust ducts used for transporting the air from domestic kitchens, bathrooms, shower rooms, lo

• CMC § 701.1 Medium relevance — show source text

  701.1, 701.1.1, 701.8, 701.10,

  802.6.3.1, 902.2, 902.12, 902.13

  Ducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (see Ducts) Economizer . . . . . . . . . . . . . . . . . (see Economizer, air) Exhaust . . . . . . . . . . . . . . . . . . . . . . . (see Air, exhaust) Filters. . . . . . . . . . . . . . . . . . . . . . . . . . . (see Filters, air) Furnace . . . . . . . . . . . . . . . . . (see Furnaces, warm air) Heaters. . . . . . . . . . . . . . . . . . . . . . . . . (see Heater, air)

  Makeup . . . . . . . . . . . . . . . 203.0, 401.1, 403.7, 504.4.1,

  505.10, 511.3, 517.1.2, 517.1.3,

  517.6.1, 517.6.2, 519.6, 701.1,

  701.3, 930.5.4, 1106.2.8, 1106.6,

  1106.11.11.1, 1220.5, E 503.4.6.9,

  E 503.5.11.3, I 801.1.4

  Moving Systems . . . . . . . . . . . . . 203.0, 609.1, I 801.1.6, Outside 203.0, Table 310.3,

  311.1, 311.3, Chapter 4,

  908.3.2, 932.1, 1105.1,

  E 502.10.2, E 805.0

  Pollution control

  devices. . . . . . . . . . . . . . . . . . . 203.0, 512.3, 512.3.5,

  513.1.1, 513.3.3

  2025 CALIFORNIA MECHANICAL CODE 571

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  INDEX

  Recirculation. . . . . . . . . . . . . . . . . . 403.3, 403.5, 403.7,

  403.9, 404.3, 407.4.5, 512.3.5

  Replacement . . . . . . . . . . . . . . . . . . . (see Air, makeup)

  Return . . . . . . . . . . . . . 203.0, 311.0, 402.3, 403.2.2.1.2,

  403.2.2.2.2, 404.3.2, 517.1.2,

  604.4, 905.6, 1105.1, Appendix E

  Supply . . . . . . . . . . 203.0, Chapter 4, 914.5, 1104.2.3.2

• CMC § 505.9 Medium relevance — show source text

  Class 4 - Ducts conveying Class 3 materials in high concentrations and highly abrasive material in high concentrations, such as alumina, bauxite, iron silicate, sand, and slag.

  Class 5 - Ducts conveying corrosives, such as acid vapors.

  505.9 Minimum Velocities and Circulation. The velocity and circulation of air in work areas shall be such that contaminant’s are captured by an airstream at the area where the emissions are generated and conveyed into a product-conveying duct system. Mixtures within work areas where contaminants are generated shall be diluted to be accordance with Section 505.3 with air that does not contain other contaminants. The velocity of air within the duct shall be not less than set forth in Table 505.9.

  Systems conveying particulate matter shall be designed by employing the constant velocity method. Systems conveying explosive or radioactive materials shall be pre-balanced through duct sizing. Other systems shall be permitted to be designed with balancing devices such as dampers. Dampers provided to balance airflow shall be provided with securely fixed minimum-position blocking devices to prevent restricting flow below the required volume or velocity. 505.10 Makeup Air. Makeup air shall be provided to replenish air exhausted by the ventilation system. Makeup air

  102 2025 CALIFORNIA MECHANICAL CODE

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  EXHAUST SYSTEMS

  intakes shall be located so as to avoid recirculation of con taminated air within enclosures.

  505.11 Hoods and Enclosures. Hoods and enclosures shall be used where contaminants originate in a concentrated area. The design of the hood or enclosure shall be such that air currents created by the exhaust systems will capture the contaminants and transport them directly to the exhaust duct. The volume of air shall be sufficient to dilute explosive or flammable vapors, fumes, or dusts in accordance with Section 505.3. Hoods of steel shall have a base metal thickness not less than 0.027 of an inch (0.686 mm) (No. 22 gauge) for Class 1 and Class 5 metal duct systems; 0.033 of an inch (0.838 mm) (No. 20 gauge) for hoods serving a Class 2 duct system; 0.044 of an inch (1.118 mm) (No. 18 gauge) for hoods serving a Class 3 duct system; and 0.068 of an inch (1.727 mm) (No. 14 gauge) for hoods serving a Class 4 duct system.

  Approved nonmetallic hoods and duct systems shall be permitted to be used for Class 5 corrosive systems where the corrosive mixture is nonflammable. Metal hoods used with Class 5 duct systems shall be protected with an approved corrosion-resistant material. Edges of hoods shall be rounded. The minimum clearance between hoods and combustible construction shall be the clearance required by the duct system.

  505.12 Pharmacies – Compounding Area of Par- enteral Solutions. [CA – Board of Pharmacy] The pharmacy shall have a designated area for the preparation of sterile products for dispensing which shall be ventilated in a manner not interfering with laminar air flow.

  Note: For additional pharmacy building standard require- ments, see Chapter 12, California Building Code.

• CMC § 8.1.3.2 Medium relevance — show source text

  CONNECTION–SEALANT METHOD

  [NFPA 96: FIGURE 8.1.3.2(c)]

  FIGURE 511.1.2(4) TYPICAL SECTION OF DUCT-TO-FAN CONNECTION-DIRECT

  TO FAN INLET CONE METHOD

  [NFPA 96: FIGURE 8.1.3.2(d)]

  2025 CALIFORNIA MECHANICAL CODE 121

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  EXHAUST SYSTEMS

  511.2.2.1 Performance Test. A performance test shall be conducted upon completion and before final approval of the installation of a ventilation system serving commercial cooking appliances. The test shall verify the rate of exhaust airflow in accordance with Section 508.5.1.2 through Section 508.5.1.5. The permit holder shall furnish the necessary test equipment and devices required to perform the tests.

  [ASHRAE 154:4.7.1]

  511.2.2.2 Capture and Containment Test. The permit holder shall verify the capture and containment performance of Type I hoods. A field test shall be conducted with all appliances under the hood at operating temperatures, all the hoods operating at design airflows, and with all sources of replacement air operating at design airflows for the restaurant. Capture and containment shall be verified visually by observing smoke or steam produced by actual cooking operation or by simulating cooking using devices such as smoke candles or smoke puffers. Smoke bombs shall not be used. [ASHRAE 154:4.7.2]

  511.2.3 Exhaust Fan Operation. A hood exhaust fan(s) shall continue to operate after the extinguishing system has been activated unless fan shutdown is required by a listed component of the ventilation system or by the design of the extinguishing system. The hood exhaust fan shall start upon actuation of the extinguishing system if the exhaust fan and all cooking equipment served by the fan have been shut down, unless fan shutdown is required by a listed component of the ventilation system or by the listing of the extinguishing system. The exhaust fan shall be provided with a means so that the fan is activated when any heat-producing cooking appliance under the hood is turned on. [NFPA 96:8.2.3.1 – 8.2.3.3]

  511.3 Makeup Air. The makeup air quantity shall prevent negative pressures in the commercial cooking area(s) from exceeding 0.02 inch water column (0.005 kPa). Where the fire-extinguishing system activates, makeup air supplied internally to a hood shall be shut off.

  For compensating hoods, where a Type I or Type II hood has an internal discharge of makeup air, the makeup air flow shall not exceed 10 percent of the exhaust airflow, the exhaust airflow shall be the net exhaust from the hood in accordance with Section 508.5.1.2 through Section 508.5.1.5. The total hood exhaust shall be determined in accordance with Equation 511.3.

  E NET = E HOOD – MA ID (Equation 511.3)

  Where:

  E NET = net hood exhaust, CFM (L/s)

  E HOOD = total hood exhaust, CFM (L/s)

• CMC § 1.1. Medium relevance — show source text

  (1) The fan for overhead range hoods and downdraft exhaust equipment not integral with the cooking appliance shall comply with UL 507.

  (2) Overhead range hoods and downdraft exhaust equipment with integral fans shall comply with UL 507.

  (3) Domestic cooking appliances with integral downdraft exhaust equipment shall comply with UL 858 or CSA/ANSI Z21.1/CSA 1.1.

  (4) Microwave ovens with integral exhaust for installation over the cooking surface shall comply with UL 923.

  (5) All domestic kitchen exhaust ducts used in conjunction with domestic range or cooktop hoods shall be constructed of metal and shall have smooth interior surfaces, fastened and sealed with duct mastic or metal tapes that meet the requirements of UL 181A.

  Exception: Ducts for domestic kitchen downdraft grillrange ventilation installed under a concrete slab floor shall be permitted to be of approved Schedule 40 PVC provided the following conditions are met:

  (1) The under-floor trench in which the duct is installed shall be completely backfilled with sand or gravel.

  (2) Not more than 1 inch (25.4 mm) of 6 inch diameter (150 mm) PVC coupling shall be permitted to protrude above the concrete floor surface.

  (3) PVC pipe joints shall be solvent cemented to provide an air and greasetight duct.

  (4) The duct shall terminate above grade outside the building and shall be equipped with a backdraft damper.

  (6) Range hoods shall discharge to the outdoors through a single wall duct and shall not terminate in an attic or crawl space.

  504.4 Clothes Dryers. A clothes dryer exhaust duct shall not be connected to a vent connector, gas vent, chimney, and shall not terminate into a crawl space, attic, or other concealed space. Exhaust ducts shall not be assembled with screws or other fastening means that extend into the duct and that are capable of catching lint, and that reduce the efficiency of the exhaust system. Exhaust ducts shall be constructed of rigid metallic material. Transition ducts used to connect the dryer to the exhaust duct shall be listed and labeled in accordance

  with UL 2158A, or installed in accordance with the clothes dryer manufacturer’s installation instructions. Clothes dryer exhaust ducts shall terminate to the outside of the building in accordance with Section 502.2.1 and shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination. Devices, such as fire or smoke dampers that will obstruct the flow of the exhaust shall not be used. Where joining of ducts, the male end shall be inserted in the direction of airflow.

  504.4.1 Provisions for Makeup Air. Makeup air shall be provided in accordance with the following:

  (1) Makeup air shall be provided for Type 1 clothes dryers in accordance with the manufacturer’s installa tion instructions. [NFPA 54:10.4.4.1] Where a closet is designed for the installation of a clothes dryer, an opening of not less than 100 square inches (0.065 m [2] ) for makeup air shall be provided in the door or by other approved means.

• CMC § 701.0 Medium relevance — show source text

  2025 CALIFORNIA MECHANICAL CODE 145

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  146 2025 CALIFORNIA MECHANICAL CODE

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  CHAPTER 7

  COMBUSTION AIR

  701.0 General.

  701.1 Applicability. Air for combustion, ventilation, and dilution of flue gases for appliances installed in buildings shall be obtained by application of one of the methods covered in Section 701.4 through Section 701.9.3. Where the requirements of Section 701.4 are not met, outdoor air shall be introduced in accordance with methods covered in Section

  701.6 through Section 701.9.3.

  Exceptions:

  (1) This provision shall not apply to direct vent appliances.

  (2) Type 1 clothes dryers that are provided with makeup air in accordance with Section 504.4.1. [NFPA 54:9.3.1.1]

  701.1.1 Other Types of Appliances. Appliances of other than natural draft design, appliances not designated as Category I vented appliances, and appliances equipped with power burners shall be provided with combustion, ventilation, and dilution air in accordance with the appliance manufacturer’s instructions. [NFPA 54:9.3.1.2]

  701.2 Pressure Difference. Where used, a draft hood or a barometric draft regulator shall be installed in the same room or enclosure as the appliance served so as to prevent any difference in pressure between the hood or regulator and the combustion air supply. [NFPA 54:9.3.1.4]

  701.3 Makeup Air. Where exhaust fans, clothes dryers, and kitchen ventilation systems interfere with the operation of appliances, makeup air shall be provided. [NFPA 54:9.3.1.5]

  701.4 Indoor Combustion Air. The required volume of indoor air shall be determined in accordance with the method

  in Section 701.4.1 or Section 701.4.2 except that where the air infiltration rate is known to be less than 0.40 ACH (air change per hour), the method in Section 701.4.2 shall be used. The total required volume shall be the sum of the required volume calculated for appliances located within the space. Rooms communicating directly with the space in which the appliances are installed through openings not furnished with doors, and through combustion air openings sized and located in accordance with Section 701.5, are considered a part of the required volume. [NFPA 54:9.3.2]

  701.4.1 Standard Method. The minimum required volume shall be 50 cubic feet per 1000 British thermal units per hour (Btu/h) (4.83 m [3] /kW). [NFPA 54:9.3.2.1]

  701.4.2 Known Air Infiltration Rate Method. Where

  the air infiltration rate of a structure is known, the minimum required volume shall be determined as follows

  [NFPA 54:9.3.2.2]:

• CMC § 140.9 Medium relevance — show source text

  Listed energy recovery devices with a sensible heat recovery effectiveness of not less than 40 percent on at least 50 percent of the total exhaust airflow; or iv. A minimum of 75 percent of makeup air volume that is:

  a. Unheated or heated to no more than 60°F; and

  b. Uncooled or cooled without the use of mechanical cooling.

  Exception to Section 140.9(b)2B: Existing hoods not being replaced as part of an addition or alteration. 3. Kitchen exhaust system acceptance. Before an occupancy permit is granted for a commercial kitchen subject to Section 140.9(b), the following equipment and systems shall be certified as meeting the acceptance requirements for code compliance, as specified by the Reference Nonresidential Appendix NA7. A certificate of acceptance shall be submitted to the enforcement agency that certifies that the equipment and systems meet the acceptance requirements specified in NA7.11.

  Exception to Section 140.9(b): Healthcare facilities.

  (c) Prescriptive requirements for laboratory and factory exhaust systems.

  1. Airflow reduction requirements. Building laboratory exhaust systems shall be able to reduce zone exhaust and makeup airflow rates to the occupied and unoccupied minimum exhaust airflow rates based on demand and sensed occupancy as follows:

  A. Occupied minimum exhaust airflow. When occupant sensing controls sense occupants in the space, the minimum exhaust and makeup airflow rates shall be the greater of: i. User-defined airflow not to exceed 1.0 cfm/ft [2] (equivalent to 6 air changes per hour for a 10-foot high ceiling); or ii. The regulated minimum occupied circulation rate documented to comply with code, accreditation, or facility environmental health and safety department requirements; or iii. The minimum needed to maintain occupied pressurization. B. Unoccupied minimum exhaust airflow. Within 20 minutes of no occupancy being detected by any occupant sensors covering the space, the minimum exhaust and makeup airflow rates shall be the greater of: i. User-defined airflow not to exceed 0.67 cfm/ft [2] (equivalent to 4 air changes per hours for a 10-foot high ceiling);

  or

  ii. The regulated minimum unoccupied circulation rate documented to comply with code, accreditation, or facility environmental health and safety department requirements; or iii. The minimum needed to maintain unoccupied pressurization. C. Applicable equipment and systems shall be certified as meeting the acceptance requirements for code compliance, as specified by the reference Nonresidential Appendix NA7.16. A certificate of acceptance shall be submitted to the enforcement agency that certifies that the equipment and systems meet the acceptance requirements specified in Nonresidential Appendix NA7.16.

  Exception to Section 140.9(c)1: New zones on an existing constant volume exhaust system. 2. Exhaust System Transfer Air. Conditioned supply air delivered to any space with mechanical exhaust shall comply with the requirements of Section 140.4(o). 3. Fan System Power Consumption. All newly installed fan exhaust systems serving a laboratory or factory with a design exhaust fan system airflow rate greater than 10,000 cfm shall meet Subsection A and either B, C, or D. Exhaust air in laboratories or factories includes all indoor air and gases removed by the exhaust system, including exhaust air from fume hoods, hazardous exhaust flows, or other manifolded exhaust streams. Exhaust fan system airflow rate is the total of the airflow rates entering the exhaust fans, which includes exhaust air and bypass air but does not include entrained or induced airflow downstream of the exhaust fans.

• CMC § 0.01 Medium relevance — show source text

  HD buffer room shall have a pressure differential of -0.01 to -0.03 inches water column in relation to the anteroom._ c. The term trauma/resuscitation room as used herein is a first-aid room and/or emergency department room used for general initial treatment of accident victims. The OR within the trauma center that is routinely used for emergency surgery is considered to be an OR by this standard. d. For operating rooms, cardiac catheterization labs, angiography rooms, cystoscopy rooms, delivery rooms, cesarean operating rooms, newborn intensive care, and class 3 imaging provide approximately 15% excess supply air to the room or a sufficient quantity of excess supply air to maintain an appropri- ate positive air balance based on the room tightness and number of doors. For all rooms not listed in this footnote or not listed in Section 322.0 requiring either a positive or negative air balance, provide approximately 10% differential cfm between supply and return/exhaust airflow but not less than 25 cfm differential shall be provided regardless of room size. Room function, size, and tightness may be considered when determining the differential airflow required. Where continuous directional control is not required, variations between supply cfm and return or exhaust cfm shall be minimized in accordance with Section 407.4.1.3.

  e. See Section 414.0 and 416.0 for AII ventilation requirements, including pressure relationship requirements, and Section 415.0 and 416.0 for PE ventilation requirements, including pressure relationship requirements.

  2025 CALIFORNIA MECHANICAL CODE 89

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  VENTILATION AIR

  f. Higher ventilation rates above the total ach listed shall be used when dictated by the laboratory program requirements and the hazard level of the potential contaminants in each laboratory work area. 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.