CMC · California Mechanical Code
Scope, applicability and termination of exhaust systems
Chapter 5 of the CMC defines which exhaust systems are regulated, requires protected outdoor terminations and prescribes minimum separation distances and hood‑specific termination rules.
Last reviewed: July 6, 2026
Overview
This portion of the California Mechanical Code (CMC) establishes which exhaust systems are covered (environmental air, product‑conveying ducts, and commercial kitchen hoods), and the basic applicability rules for Chapter 5. See §501.1 for the chapter scope and applicability.
It also sets basic requirements for outdoor terminations and protection of exhaust openings (for example, required corrosion‑resistant screening at outdoor outlets is specified in §502.1), and requires exhaust ducts to terminate outside the building except as specifically allowed. These provisions exist to protect public health, avoid nuisance or hazards, and to separate incompatible exhausts or contaminants.
Key termination rules are organized by the class of air being exhausted (environmental/Class 1–4, product‑conveying, flammable/combustible, etc.). Section §502.2 (with subsections §502.2.1–§502.2.3) gives the minimum separation and elevation distances from property lines, openings, intakes and grade; commercial kitchen hood terminations are governed by the Type I and Type II hood rules in §510.9 and §519.5 respectively.
In this section
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 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
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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 § 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
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CMC § 519.0 High relevance — show source text
519.0 Type II Hood Exhaust System Requirements . . . . . . . . . . . . . . . . 132
519.1 Where Required . . . . . . . . . . . . . . 132
519.2 Construction of Type II Hoods . . . 132
519.3 Type II Hood Exhaust System Net Airflow . . . . . . . . . . . . . . . . . . 132
519.4 Type II Exhaust Duct Systems . . . 132
519.5 Termination of Type II Hood Exhaust System . . . . . . . . . . . . . . 132
519.6 Makeup Air . . . . . . . . . . . . . . . . . . 133
519.7 Independent Exhaust Duct System . . . . . . . . . . . . . . . . . 133
CHAPTER 6 DUCT SYSTEMS . . . . . . . . . . . . . 135
601.0 General. . . . . . . . . . . . . . . . . . . . . 137
601.1 Applicability. . . . . . . . . . . . . . . . . . 137
601.2 Sizing Requirements . . . . . . . . . . 137
602.0 Material. . . . . . . . . . . . . . . . . . . . . 137
602.1 General. . . . . . . . . . . . . . . . . . . . . 137
602.2 Combustibles Within Ducts or
Plenums . . . . . . . . . . . . . . . . . . . . 137
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602.3 Tall Wood (Mass Timber) Buildings . . . . . . . . . . . . . . . . . . . . 137
602.4 Metallic . . . . . . . . . . . . . . . . . . . . . 138
602.5 Nonmetallic Ducts. . . . . . . . . . . . . 138
602.6 Vibration Isolators. . . . . . . . . . . . . 138
602.7 Corridors. . . . . . . . . . . . . . . . . . . . 138
603.0 Installation of Ducts . . . . . . . . . . . 138
603.1 General. . . . . . . . . . . . . . . . . . . . . 138
603.2 Under-Floor or Crawl Space. . . . . 138
603.3 Metal Ducts. . . . . . . . . . . . . . . . . . 138
603.4 Flexible Air Ducts . . . . . . . . . . . . . 138
603.5 Plastic Ducts. . . . . . . . . . . . . . . . . 139
603.6 Protection of Ducts . . . . . . . . . . . . 139
603.7 Support of Ducts. . . . . . . . . . . . . . 139
603.8 Protection Against Flood Damage . 139
603.9 Joints and Seams of Ducts. . . . . . 139
Table 603.9.1 Closure Markings . . . . . . . . . . . . . 140
CMC § 519.4 High relevance — show source text
519.4 Type II Exhaust Duct Systems. Ducts and plenums serving Type II hoods shall be constructed of rigid metallic materials in accordance with Chapter 6. Duct bracing and supports shall comply with Chapter 6. Ducts subject to positive pressure shall be adequately sealed.
519.5 Termination of Type II Hood Exhaust System. The exhaust system shall terminate in accordance with Section 502.2.2. Rooftop terminations shall be directed away
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from roof surfaces within 40 inches (1016 mm). The discharge outlet of moisture conveying exhaust ducts, such as dishwasher exhaust ducts, shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.
519.6 Makeup Air. Makeup air shall be provided in accordance with Section 511.3.
519.7 Independent Exhaust Duct System. Single or combined Type II exhaust systems shall be independent of all other exhaust systems.
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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE
CHAPTER 6 – DUCT SYSTEMS
(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
Adopting Agency BSC BSC-
CGSFM HCD Col6 Col7 DSA Col9 Col10 OSHPD Col12 Col13 Col14 Col15 Col16 Col17 BSCC DPH AGR DWR CEC CA SL SLC Adopting Agency BSC BSC-
CGSFM 1 2 1-AC AC ** SS** ** SS/CC** 1 1R 2 3 4 5 6 6 6 6 6 6 6 6 6 Adopt Entire Chapter X X X Adopt Entire Chapter as
amended (amended sections
listed below)X X X X X X X X X Adopt only those sections
that are listed belowX Chapter/Section _601.2. CMC § 510.3 Medium relevance — show source text
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EXHAUST SYSTEMS
on the top portion of the grease duct in accordance with Section 510.3 and shall be labeled at the interior portion of the duct.
510.9 Termination of Type I Hood Exhaust System. The exhaust system shall terminate as follows:
(1) Outside the building with a fan or duct.
(2) Through the roof or to the roof from outside, as in Section 510.9.1, or through a wall, as in Section 510.9.2. [NFPA 96:7.8.1] 510.9.1 Rooftop Terminations. Rooftop terminations shall be arranged with or provided with the following:
(1) A minimum of 10 feet (3048 mm) of horizontal clearance from the outlet to adjacent buildings, property lines, and air intakes.
(2) A minimum of 5 feet (1524 mm) of horizontal clearance from the outlet (fan housing) to any combustible structure.
(3) A vertical separation of 3 feet (914 mm) above any air intakes within 10 feet (3048 mm) of the exhaust outlet.
(4) The ability to drain grease out of any traps or low points formed in the fan or duct near the termination of the system into a collection container that is noncombustible, closed, rainproof, and structurally sound for the service to which it is applied and that will not sustain combustion.
(5) A grease collection device that is applied to exhaust systems that does not inhibit the performance of any fan.
(6) Grease collection systems that meet the requirements of Section 510.9.1(4) and Section 510.9.1(5).
(7) A listed grease duct complying with Section 507.4.7 or ductwork complying with Section 507.4.8.
(8) A hinged upblast fan supplied with flexible weatherproof electrical cable and service hold-open retainer to permit inspection and cleaning that is listed for commercial cooking equipment with the following conditions:
(a) Where the fan attaches to the ductwork, the ductwork is a minimum of 18 inches (457 mm) away from any roof surface, as shown in Figure 510.9.1.
(b) The fan discharges a minimum of 40 inches (1016 mm) away from any roof surface, as shown in Figure 510.9.1.
(9) Other approved fan, provided it meets all of the following criteria:
(a) The fan meets the requirements of Section 510.9.1(3) and Section 511.1.3.
(b) Its discharge or its extended duct discharge meets the requirements of Section 510.9.1(2). (See Section 511.1.3)
(c) Exhaust fan discharge is directed up and away from the roof surface. {NFPA 96:7.8.2.1}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
FIGURE 510.9.1
UPBLAST FAN CLEARANCES
[NFPA 96: FIGURE 7.8.2.1]
510.9.1.1 Listed Vibration Isolation Connec-
CMC § 502.2.4 Medium relevance — show source text
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CHAPTER 5
EXHAUST SYSTEMS
502.2.4 Commercial Kitchen Ducts. Commercial
kitchens exhaust ducts shall terminate in accordance with
Section 510.9 for Type I exhaust systems or Section 519.5 for Type II exhaust systems.
Part I – Environmental Air Ducts and Product-Conveying Systems.
503.0 Motors, Fans, and Filters.
503.1 General. Motors and fans shall be sized to provide the required air movement. Motors in areas that contain flammable vapors or dusts shall be of a type approved for such environments. A manually operated remote control installed at an approved location shall be provided to shut off fans or blowers in flammable vapor or dust systems. Equipment used in operations that generate explosive or flammable vapors, fumes, or dusts shall be interlocked with the ventilation system so that the equipment cannot be operated unless the ventilation fans are in operation. Motors for fans used to convey flammable vapors or dusts shall be located outside the duct or shall be protected with approved shields and dustproofing. Where belts are used, they shall not enter the duct unless the belt and pulley within the duct are enclosed. Motors and fans shall be accessible for servicing and maintenance.
503.2 Fans. Parts of fans in contact with explosive or flammable vapors, fumes, or dusts shall be of nonferrous or nonsparking materials, or their casing shall be lined or constructed of such material. Where the size and hardness of
materials passing through a fan are capable of producing a spark, both the fan, and the casing shall be of nonsparking materials. Where fans are required to be spark-resistant, their bearings shall not be within the airstream, and parts of the fan shall be grounded. Fans in systems handling materials that are likely to clog the blades, and fans in buffing or woodworking exhaust systems, shall be of the radial-blade or tube-axial type.
Equipment used to exhaust explosive or flammable vapors, fumes, or dusts shall bear an identification plate stating the ventilation rate for which the system was designed.
Fans located in systems conveying corrosives shall be of materials that are resistant to the corrosive or shall be coated
with corrosion-resistant materials.
504.0 Environmental Air Ducts.
504.1 General. Where not specified in this chapter, exhaust ducts shall be constructed and installed in accordance with
Chapter 6 and shall be airtight as approved by the Authority Having Jurisdiction. Environmental air ducts that have an alternate function as a part of an approved smoke control sys
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501.0 General.
501.1 Applicability. This chapter includes requirements for environmental air ducts, product-conveying systems, and commercial hoods and kitchen ventilation. Part I addresses environmental air ducts and product conveying systems. Part II addresses commercial hoods and kitchen ventilation.
502.0 Termination.
502.1 Exhaust Opening Protection. Exhaust openings terminating to the outdoors shall be covered with a corrosionresistant screen having not less than [1] ⁄ 4 of an inch (6.4 mm) openings, and shall have not more than [1] ⁄ 2 of an inch (12.7 mm) openings.
CMC § 516.4 Medium relevance — show source text
516.4 Location and Application Restrictions. . . . . . . . . . . . . . . . . . 129
516.5 Additional Fire Safety Requirements . . . . . . . . . . . . . . . . 129
516.6 Use and Maintenance. . . . . . . . . . 129
517.0 Solid-Fuel Cooking Operations. . . 129
517.1 Venting Application. . . . . . . . . . . . 129
517.2 Location of Appliances . . . . . . . . . 130
517.3 Hoods for Solid-Fuel Cooking. . . . 130
517.4 Exhaust Systems for Solid-Fuel Cooking . . . . . . . . . . . . 130
517.5 Grease Removal Devices
for Solid-Fuel Cooking . . . . . . . . . 130
517.6 Air Movement for Solid-Fuel
Cooking . . . . . . . . . . . . . . . . . . . . 130
517.7 Fire-Extinguishing Equipment for Solid-Fuel Cooking . . . . . . . . . 131
517.8 Other Safety Requirements . . . . . 131
518.0 Downdraft Appliances. . . . . . . . . . 131
518.1 General. . . . . . . . . . . . . . . . . . . . . 131
518.2 Ventilation System . . . . . . . . . . . . 132
518.3 Fire-Extinguishing Equipment. . . . 132
518.4 Airflow Switch or Transducer . . . . 132
518.5 Surface Materials . . . . . . . . . . . . . 132
519.0 Type II Hood Exhaust System Requirements . . . . . . . . . . . . . . . . 132
519.1 Where Required . . . . . . . . . . . . . . 132
519.2 Construction of Type II Hoods . . . 132
519.3 Type II Hood Exhaust System Net Airflow . . . . . . . . . . . . . . . . . . 132
519.4 Type II Exhaust Duct Systems . . . 132
519.5 Termination of Type II Hood Exhaust System . . . . . . . . . . . . . . 132
519.6 Makeup Air . . . . . . . . . . . . . . . . . . 133
519.7 Independent Exhaust Duct System . . . . . . . . . . . . . . . . . 133
CHAPTER 6 DUCT SYSTEMS . . . . . . . . . . . . . 135
601.0 General. . . . . . . . . . . . . . . . . . . . . 137
601.1 Applicability. . . . . . . . . . . . . . . . . . 137
601.2 Sizing Requirements . . . . . . . . . . 137
602.0 Material. . . . . . . . . . . . . . . . . . . . . 137
602.1 General. . . . . . . . . . . . . . . . . . . . . 137
602.2 Combustibles Within Ducts or
Plenums . . . . . . . . . . . . . . . . . . . . 137
CMC § 403.9.2. Medium relevance — show source text
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.
I 801.1.6 Automatic Shutoff. Automatic shutoff in air moving systems shall be provided in accordance with Section 609.0.
I 901.0 Particulate and Odor Control.
I 901.1 General. Particulates and odors from indoor horticultural cultivation and processing of plants for human ingestion, inhalation, and topical application shall be filtered and controlled so that it is not detectable above nuisance levels not exceeding applicable exposure limits at the exterior of the facility or at adjoining properties or as required by the Authority Having Jurisdiction. Odor control shall be required in the exhaust system and shall include, but not be limited to, one or more of the following types:
(1) Charcoal filters shall be installed on the discharge of all exhaust ducts and shall be installed in accordance with
the manufacturer’s installation instructions.
(2) Ozone generators shall be installed in all exhaust ducts to neutralize odor by oxidizing such odors with ozone.
(3) Ionizers shall be installed in accordance with the manufacturer’s installation instructions.
(4) Photo-catalytic oxidation shall be installed in accordance with the manufacturer’s installation instructions.
(5) Photo-hydroxyl oxidation shall be installed in accordance with the manufacturer’s installation instructions.
(6) Carbon filtration shall be installed in accordance with the manufacturer’s installation instructions.
(7) UV-C lights shall be installed in accordance with the manufacturer’s installation instructions.
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APPENDIX I
(8) Where approved by the Authority Having Jurisdiction, a plume discharge termination method shall be permitted to be used for odor control. The exhaust fan of such a
CMC § 504.0 Medium relevance — show source text
Equipment used to exhaust explosive or flammable vapors, fumes, or dusts shall bear an identification plate stating the ventilation rate for which the system was designed.
Fans located in systems conveying corrosives shall be of materials that are resistant to the corrosive or shall be coated
with corrosion-resistant materials.
504.0 Environmental Air Ducts.
504.1 General. Where not specified in this chapter, exhaust ducts shall be constructed and installed in accordance with
Chapter 6 and shall be airtight as approved by the Authority Having Jurisdiction. Environmental air ducts that have an alternate function as a part of an approved smoke control sys
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501.0 General.
501.1 Applicability. This chapter includes requirements for environmental air ducts, product-conveying systems, and commercial hoods and kitchen ventilation. Part I addresses environmental air ducts and product conveying systems. Part II addresses commercial hoods and kitchen ventilation.
502.0 Termination.
502.1 Exhaust Opening Protection. Exhaust openings terminating to the outdoors shall be covered with a corrosionresistant screen having not less than [1] ⁄ 4 of an inch (6.4 mm) openings, and shall have not more than [1] ⁄ 2 of an inch (12.7 mm) openings.
Exception: Clothes dryers.
502.2 Termination of Exhaust Ducts. Exhaust ducts shall terminate in accordance with Section 502.2.1 through Section 502.2.4. Classes of air shall be as defined in Section
203.0 and classified in Section 403.9.
502.2.1 Environmental, Class 1, and Class 2 Air Ducts. Environmental, Class 1, and Class 2 air duct exhaust shall terminate not less than 3 feet (914 mm) from a property line, 10 feet (3048 mm) above a public way, 3 feet (914 mm) from openings into the building and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1. The discharge of dryer exhaust ducts shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.
502.2.2 Class 3 Air Ducts. Class 3 air duct exhaust shall terminate not less than 10 feet (3048 mm) from a property line, 3 feet (914 mm) from exterior walls or roofs that are in the direction of the exhaust discharge, 10 feet (3048 mm) from openings into the building, 10 feet (3048 mm) above adjoining grade, and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1.
CMC § 510.9. Medium relevance — show source text
Exception: Type I Hood exhaust termination shall be in accordance with Section 510.9.
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tem in accordance with Section 505.7.3 do not require design as Class 1 product-conveying ducts.
Exceptions:
(1) Ductless range hoods where installed in accordance with the manufacturer’s installation instructions.
(2) Condensing clothes dryers where installed in accordance with the manufacturer’s installation instructions.
504.1.1 Backdraft Protection. Exhaust ducts shall terminate outside the building and shall be equipped with backdraft dampers or with motorized dampers that automatically shut where the systems or spaces served are not in use. [OSHPD 1, 1R, 2, 4 & 5] Exception: Back- draft dampers are not required when the exhaust fan must operate continuously.
Exception: Where the exhaust duct does not discharge into a common exhaust plenum and one of the following:
(1) The exhaust fan runs continuously.
(2) The exhaust duct serves space(s) that are not mechanically heated or cooled.
(3) The space served is maintained at positive pressure. 504.2 Independent Exhaust Systems. Single or combined mechanical exhaust systems for environmental air shall be independent of other exhaust systems. Combined exhaust systems shall operate at negative pressure and shall terminate in accordance with Section 502.2.1. Clothes dryer exhaust systems shall be independent of all other exhaust systems except where permitted in Section 504.4.4. 504.3 Domestic Cooking Exhaust Equipment. Domestic cooking exhaust equipment shall comply with the following requirements, as applicable:
(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.
CMC § 502.2 Medium relevance — show source text
Exception: Clothes dryers.
502.2 Termination of Exhaust Ducts. Exhaust ducts shall terminate in accordance with Section 502.2.1 through Section 502.2.4. Classes of air shall be as defined in Section
203.0 and classified in Section 403.9.
502.2.1 Environmental, Class 1, and Class 2 Air Ducts. Environmental, Class 1, and Class 2 air duct exhaust shall terminate not less than 3 feet (914 mm) from a property line, 10 feet (3048 mm) above a public way, 3 feet (914 mm) from openings into the building and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1. The discharge of dryer exhaust ducts shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.
502.2.2 Class 3 Air Ducts. Class 3 air duct exhaust shall terminate not less than 10 feet (3048 mm) from a property line, 3 feet (914 mm) from exterior walls or roofs that are in the direction of the exhaust discharge, 10 feet (3048 mm) from openings into the building, 10 feet (3048 mm) above adjoining grade, and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1.
502.2.3 Product Conveying, Flammable, and Class 4 Air Ducts. Ducts conveying Class 4 air or explosive or flammable vapors, fumes, or dusts shall terminate not less than 30 feet (9144 mm) from a property line, 10 feet (3048 mm) from openings into the building, 6 feet (1829 mm) from exterior walls or roofs that are in the direction of the exhaust discharge, 30 feet (9144 mm) from combustible walls or openings into the building that are in the direction of the exhaust discharge, 10 feet (3048 mm) above adjoining grade, and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1.
Exception: Type I Hood exhaust termination shall be in accordance with Section 510.9.
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EXHAUST SYSTEMS
tem in accordance with Section 505.7.3 do not require design as Class 1 product-conveying ducts.
Exceptions:
(1) Ductless range hoods where installed in accordance with the manufacturer’s installation instructions.
(2) Condensing clothes dryers where installed in accordance with the manufacturer’s installation instructions.
504.1.1 Backdraft Protection. Exhaust ducts shall terminate outside the building and shall be equipped with backdraft dampers or with motorized dampers that automatically shut where the systems or spaces served are not in use. [OSHPD 1, 1R, 2, 4 & 5] Exception: Back- draft dampers are not required when the exhaust fan must operate continuously.
Exception: Where the exhaust duct does not discharge into a common exhaust plenum and one of the following:
(1) The exhaust fan runs continuously.
CMC § 4.1 Medium relevance — show source text
4.1||||||||||†||†|†|†|†|||||||||| |603.4.1.1||||||||||X||X|X|X|X|||||||||| |603.9.2||||†|†|||||||||||||||||||| |603.9.2.1|||||||||||||||||||||X|||| |605.1||||||||||X|X|X|X|X|X|||||||||| |605.2||||||||||X|||X|X|X|||||||||| |605.3||||||||||X||X||X|X|||||||||| |606.1||||X|X|||||||||||||||||||| |606.4.1|||X|||||||||||||||||||||| |607.1.1||||||||||X|X|X|X|X|X|||||||||| |609.1|||X|||||||||||||||||||||| |609.1.1|||X|||||||||||||||||||||| |609.2|||X||||||||||||||||||||||
This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.
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CHAPTER 6
DUCT SYSTEMS
601.0 General.
601.1 Applicability. Ducts and plenums that are portions of a heating, cooling, ventilation, or exhaust system shall comply with the requirements of this chapter, Chapter 5 for exhaust ducts, and Chapter 7 for combustion air ducts. 601.2 Sizing Requirements. Duct systems shall be sized in accordance with applicable standards in Chapter 18 or by other approved methods.
Exception: Residential duct systems shall be sized in accordance with ACCA Manual D, ACCA Manual Zr, as applicable, or by other approved methods.
601.2.1 California Energy Code Residential Return Duct Sizing Requirements. California Energy Code Tables 150.0-B and 150.0-C specify return duct sizing requirements for single return and multiple return duct systems, respectively, that are applicable as an alternative to confirming system airflow via field verification and diagnostic testing. See California Energy Code Section 150.0(m)13 for provisions applicable to newly con- structed buildings, and Section 150.2(b)(1)(F)(ii)(a) for alterations.
602.0 Material.
602.1 General. Materials used for duct systems shall comply with Section 602.2 through Section 602.7 as applicable. Exception: [OSHPD 1, 1R, 2, 3, 4 & 5] See Section 407.4.2.
Frequently asked questions
What sections define which exhaust systems are included and when they apply?
Chapter 5 sets the scope; see §501.0 and §501.1 for what the chapter covers (environmental air ducts, product‑conveying systems, and commercial hoods) and their applicability.
How far must an exhaust outlet be from air intakes, openings or property lines?
Required distances depend on the air classification. For environmental/Class 1–2 ducts see §502.2.1; Class 3 and Class 4/product or flammable exhausts have larger minimum separations in §502.2.2 and §502.2.3 respectively. Commercial kitchen hood terminations follow §510.9 (Type I) and §519.5 (Type II).
Are screens, backdraft dampers or independent ducts required?
Outdoor exhaust openings must be covered with corrosion‑resistant screening per §502.1 (exceptions such as clothes dryers are noted). Exhaust ducts are generally required to terminate outside and be equipped with backdraft protection where indicated; environmental exhausts should be independent of other exhaust systems except as specifically allowed.
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