CRC · California Residential Code
Combustion air, chimneys and vents — CRC guidance and CMC chapters to consult
In California the Residential Code does not adopt the model Chapters 17 and 18 for combustion air and chimneys — those subjects are regulated by the California Mechanical Code (CMC Chapter 7 for combustion air and Chapter 8 for chimneys/vents). For fireplaces the CRC retains § R1006 (exterior air supply and passageway/outlet sizing). Key field rules you’ll see most often: combustion‑air openings must be properly sized, screened and not fitted with manual dampers (CMC **§ 701.10–701.12**), and chimneys must meet the termination height rules (CMC **§ 802.5.4**). Always follow appliance listing/manufacturer instructions and the CMC tables for sizing.
Last reviewed: July 6, 2026
What the code requires — plain English with the controlling §
- The California Residential Code (CRC) does not adopt the model Chapter 17 — Combustion Air or Chapter 18 — Chimneys & Vents; instead, those topics are regulated by the California Mechanical Code (CMC), Title 24, Part 4 (consult CMC Chapter 7 and CMC Chapter 8).
- For residential fireplaces the CRC retains a fireplace-specific combustion-air section: § R1006 (exterior air supply, passageway sizes, outlet location) — use that for fireplaces and otherwise default to the CMC for general appliance combustion-air and venting.
The single most important point: CRC Chapters 17 and 18 are not adopted in California — use CMC Chapter 7 (Combustion Air) and CMC Chapter 8 (Chimneys & Vents) for appliance combustion-air and venting details.
Requirements in detail
Where to look (controlling chapters)
- CRC: § R1006 (Exterior air supply — fireplaces).
- CMC: § 701.0 et seq. (Chapter 7 — Combustion Air) and § 801.0 et seq. / § 802.0 et seq. (Chapter 8 — Chimneys & Vents).
Key rules summarized (CMC Chapter 7 — Combustion air)
- Combustion air must be adequate for safe combustion, ventilation and dilution of flue gases; acceptable supply methods include indoor air, outdoor air, or a combination and engineered or mechanical supply where required (see § 701.1–701.9).
- Duct construction: Combustion air ducts must be constructed of galvanized steel or equivalent and terminate to an unobstructed space; ducts shall serve a single space and meet several installation constraints (see § 701.11).
- Louvers / screens: Screens must be at least 1/4‑inch (6.4 mm) mesh; motorized louvers must be interlocked so the main burner cannot fire unless the louvers are fully open (see § 701.10, § 701.10.1, § 701.10.2).
- Dampers prohibited: Manually operated dampers are not permitted in combustion air openings; power‑actuated louvers may be allowed only when electrically interlocked (see § 701.12).
Key rules summarized (CMC Chapter 8 — Chimneys & Vents)
- Applicability & listing: Venting of gas appliances and other fuels is governed by Chapter 8; vents and chimneys must be listed where required and installed per the manufacturer and Chapter 8 rules (see § 801.1, § 802.1, § 802.1.1).
- Chimney height & termination: A residential/low‑heat chimney shall extend at least 3 ft above the highest point where it passes through a roof and at least 2 ft higher than any portion of a building within a horizontal distance of 10 ft (see § 802.5.4).
- Chimney sizing: The effective area of a chimney serving appliances with draft hoods (Category I appliances) shall follow one of the sizing methods in § 803.0 / § 802.5.5 (tables or the area‑ratio rules — e.g., not less than the flue‑collar area and not greater than seven times the draft‑hood outlet unless engineered).
- Venting material & special vents: Plastic vents, gas vents, factory‑built chimneys, single‑wall pipe, etc., have specific listing and installation requirements and clearances in § 802.4–802.7 and related tables.
Decision‑relevant dimensions/values (quick reference table)
| Topic | Key value / threshold | Code Reference |
|---|---|---|
| CRC: Fireplace exterior air supply — passageway area | 6 in² minimum, 55 in² maximum | § R1006.4 |
| CRC: Fireplace exterior air outlet location | Outlet ≤ 24 in from firebox opening (at hearth level/back/side) | § R1006.5 |
| CMC: Exterior combustion-air intake elevation | Lowest side ≥ 12 in above adjoining finished ground | § 701.11(8) |
| CMC: Chimney height (residential) | ≥ 3 ft above roof penetration; ≥ 2 ft higher than any part of building within 10 ft horizontal | § 802.5.4 |
| CMC: Chimney flue area limits | Chimney flue ≥ flue-collar area; ≤ 7× draft‑hood outlet area (unless engineered) | § 802.5.5 |
| CMC: Combustion air ducts — material | Galvanized steel or equivalent corrosion‑resistant material | § 701.11(1) |
| CMC: Screens | 1/4‑inch (6.4 mm) mesh minimum | § 701.10.1 |
| CMC: Dampers | Manually operated dampers prohibited in combustion-air openings | § 701.12 |
(Always verify appliance‑specific manufacturer instructions and the applicable CMC tables for vent sizing and material selection; Chapter 8 tables perform many of the engineering calculations.)
Exceptions & special cases
- CRC fireplaces: The CRC retains fireplace‑specific combustion‑air rules; where a fireplace is listed with a factory‑built exterior air duct, the duct must be installed per the manufacturer’s listed instructions (§ R1006.1.1 / R1006.1.2).
- Direct‑vent appliances: CMC includes exceptions for direct‑vent appliances in several places (they are not always regulated by the combustion‑air provisions the same way) — consult the appliance listing and § 701.1 and related exceptions.
- Engineered installations: Where standard tabulated methods do not apply (multi‑appliance common vents, unusual exposures, long offsets, high external portions), the code requires engineered design per § 701.8 and the vent sizing chapters (see Chapter 8 for engineering methods and reductions).
Common mistakes
- Relying on CRC Chapters 17 or 18 for appliance venting — those chapters are not adopted; use CMC Chapter 7 and 8.
- Installing manual dampers in combustion‑air openings — prohibited by § 701.12.
- Using attic/chimney chase voids as combustion‑air ducts without meeting the specific exceptions/requirements (CMC § 701.11 prohibits certain uses).
- Incorrect chimney termination height — failure to meet the 3 ft / 2 ft within 10 ft rule in § 802.5.4 is a frequent field violation.
- Ignoring appliance listing/manufacturer instructions — the code repeatedly requires installation in accordance with the manufacturer for listed appliances (see § 802.1.1).
Worked example — chimney termination (numbers)
Scenario: A gas fireplace’s factory‑built chimney passes through the roof of a house. There is a gable roof ridge 8 ft horizontally from the chimney and the ridge is 1 ft higher than the chimney’s roof penetration elevation.
Code check:
- Per § 802.5.4, the chimney must extend at least 3 ft above the highest point where it passes through the roof. That gives a baseline of +3 ft above the roof penetration.
- Also per § 802.5.4, the chimney must be at least 2 ft higher than any portion of the building within 10 ft horizontally. The nearby ridge is within 10 ft and is 1 ft higher, so the chimney must be 2 ft higher than that ridge — i.e., 2 ft above the ridge. Since the ridge is 1 ft above the roof penetration, that equals 3 ft above the roof penetration (1 ft + 2 ft).
Conclusion: Both criteria produce the same numeric requirement in this scenario: the chimney must extend 3 ft above the roof penetration. If the nearby roof portion had been taller such that the "2 ft above any portion within 10 ft" produced a larger value, the chimney would have to meet that larger height. Always select the greater of the required heights.
Related provisions (quick list)
- CRC: § R1006.1 — Exterior air supply for fireplaces.
- CRC: § R1006.4 — Combustion‑air passageway area limits for fireplaces.
- CMC: § 701.0 – § 701.12 — Chapter 7 Combustion Air (general requirements, ducts, louvers, dampers).
- CMC: § 801.0 – § 803.0 — Chapter 8 Chimneys & Vents (listing, connections, sizing, materials).
- CMC: § 802.1.1 — Listed chimneys and vents must be installed per manufacturer instructions.
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CMC § 2025 High relevance — show source text
Chapter 7 Combustion Air. Chapter 7 regulates combustion air requirements for ventilation and dilution of flue gases for appliances installed in buildings. Fuel-gas appliances not regulated by chapter include direct vent appliances and Type I clothes dryers. Makeup air requirements for Type I clothes dryers are located in Chapter 5. Chapter 7 provides acceptable methods for supplying satisfactory combustion air to ensure proper combustion. Combustion air can be supplied by using indoor combustion air or by introducing the air from the outdoors.
Combustion is the rapid oxidation of fuel to release energy. The oxygen required to release the energy from the fuel normally comes from the air. Incomplete combustion of fuel occurs when inadequate oxygen is provided to the appliance. Combustion is needed to provide ventilation cooling for the casing and internal controls. When a lack of oxygen occurs, some of the carbon is not oxidized, and carbon monoxide forms.
Chapter 8 Chimneys and Vents. Chapter 8 regulates the installation, design, and construction of venting systems for fuel-burning appliances. The provisions addressed within this chapter follow procedures an installer would use to design or evaluate a venting system. Many requirements apply to the design and construction of venting systems, chimneys, installation of gas vents, and the sizing of venting system for a Category I appliance. Sizing venting systems require rigorous engineering calculations. However, the venting sizing requirements and sizing tables in this chapter already perform the calculations for the benefit of the end user.
Combustion appliances produce products of incomplete combustion, including potentially harmful carbon monoxide (CO). It is desirable to vent these products to the outdoors. Although the gas is clean-burning fuel, the products of combustion must not be allowed to collect within a building.
Chapter 9 Installation of Specific Appliances. Chapter 9 regulates the minimum requirements for the design, construction and installation of specific appliances. The provisions address the minimum requirements for gas-fired appliances, oil-fired appliances, wood-fired appliances, and electric-type appliances. In addition to the requirements of this chapter, appliances are also required to comply with the general requirements of Chapter 3.
Chapter 10 Boilers and Pressure Vessels. Chapter 10 regulates the construction, installation, operation, repair, and alteration of boilers and pressure vessels. The safety provisions within this chapter address controls and limit devices for automatic boilers, methods of determining expansion tank capacities, discharge piping, relief valves, shutoff valves, gas-pressure and combustion regulators, and inspections and tests. Potable water heaters are free from the requirements of Chapter 10 as they are within the scope of the Uniform Plumbing Code (UPC).
Pressure vessels store large amounts of energy and must comply with ASME Boiler and Pressure Vessel Code (BPVC) Section VIII.1. The stored energy must be contained to prevent disastrous failures. Boilers must comply with ASME BPVC Section I, ASME BPVC Section IV, or NFPA 85. Installing a safety relief valve and expansion tank prevents pressures in the tank from exceeding the design threshold.
Chapter 11 Refrigeration. Chapter 11 regulates the design, installation, and construction requirements of refrigeration systems and the installation and construction of cooling towers. Refrigeration is a method used for achieving heat transfer to cool spaces. Refrigerants are the most common medium used to transfer the heat energy from the low-temperature level to the high-temperature level. Table
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FORMAT OF THE UNIFORM MECHANICAL CODE
CMC § 2025 High relevance — show source text
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
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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.
Chapter 7 Combustion Air. Chapter 7 regulates combustion air requirements for ventilation and dilution of flue gases for appliances installed in buildings. Fuel-gas appliances not regulated by chapter include direct vent appliances and Type I clothes dryers. Makeup air requirements for Type I clothes dryers are located in Chapter 5. Chapter 7 provides acceptable methods for supplying satisfactory combustion air to ensure proper combustion. Combustion air can be supplied by using indoor combustion air or by introducing the air from the outdoors.
Combustion is the rapid oxidation of fuel to release energy. The oxygen required to release the energy from the fuel normally comes from the air. Incomplete combustion of fuel occurs when inadequate oxygen is provided to the appliance. Combustion is needed to provide ventilation cooling for the casing and internal controls. When a lack of oxygen occurs, some of the carbon is not oxidized, and carbon monoxide forms.
Chapter 8 Chimneys and Vents. Chapter 8 regulates the installation, design, and construction of venting systems for fuel-burning appliances. The provisions addressed within this chapter follow procedures an installer would use to design or evaluate a venting system. Many requirements apply to the design and construction of venting systems, chimneys, installation of gas vents, and the sizing of venting system for a Category I appliance. Sizing venting systems require rigorous engineering calculations. However, the venting sizing requirements and sizing tables in this chapter already perform the calculations for the benefit of the end user.
Combustion appliances produce products of incomplete combustion, including potentially harmful carbon monoxide (CO). It is desirable to vent these products to the outdoors. Although the gas is clean-burning fuel, the products of combustion must not be allowed to collect within a building.
CRC § 1.11.0. High relevance — show source text
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 X X X X X X X X X Adopt Entire Chapter as
amended (amended sections
listed below)Adopt only those sections
that are listed belowChapter/Section This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.
2025 CALIFORNIA MECHANICAL CODE 151
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152 2025 CALIFORNIA MECHANICAL CODE
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CHAPTER 8
CHIMNEYS AND VENTS
801.0 General.
801.1 Applicability. The requirements of this chapter shall govern the venting of fuel-burning appliances.
801.2 Venting of Gas Appliances. Low-heat and medium-heat gas appliances shall be vented in accordance with this chapter. Other gas appliances shall be vented in accordance with NFPA 211 or other applicable standards.
801.3 Appliances Fueled by Other Fuels. Appliances fueled by fuels other than gas shall be vented in accordance with NFPA 211 and the appliance manufacturer’s instructions.
802.0 Venting of Appliances.
802.1 Listing. Type B and Type B-W gas vents shall comply with UL 441, Type L gas vents shall comply with UL 641.
802.1.1 Installation. Listed chimneys and vents shall be installed in accordance with this chapter and the manufacturer’s installation instructions. [NFPA 54:12.2.1]
CRC § 608.9 High relevance — show source text
608.9 Floor Registers . . . . . . . . . . . . . . . 143
608.10 Exterior Wall and Interior Stud
Partitions. . . . . . . . . . . . . . . . . . . . 143
608.11 Wall Register . . . . . . . . . . . . . . . . 143
608.12 Distance from Combustible . . . . . 143
608.13 Vapor Barrier . . . . . . . . . . . . . . . . 143
608.14 Prohibited . . . . . . . . . . . . . . . . . . . 143
609.0 Automatic Shutoffs . . . . . . . . . . . . 143
609.1 Air-Moving Systems and Smoke Detectors . . . . . . . . . . . . . . . . . . . 143
609.2 Air-Moving Systems and Smoke Detectors in Group I-2 Occupancies . . . . . . . . . . . . . . . . 144
CHAPTER 7 COMBUSTION AIR . . . . . . . . . . . 145
701.0 General. . . . . . . . . . . . . . . . . . . . . 147
701.1 Applicability. . . . . . . . . . . . . . . . . . 147
701.2 Pressure Difference . . . . . . . . . . . 147
701.3 Makeup Air . . . . . . . . . . . . . . . . . . 147
701.4 Indoor Combustion Air . . . . . . . . . 147
701.5 Indoor Opening Size and Location . . . . . . . . . . . . . . . . . . . . 147
701.6 Outdoor Combustion Air . . . . . . . . 147
701.7 Combination Indoor and Outdoor
Combustion Air . . . . . . . . . . . . . . . 148
701.8 Engineered Installations . . . . . . . . 149
701.9 Mechanical Combustion Air
Supply. . . . . . . . . . . . . . . . . . . . . . 149
701.10 Louvers, Grilles, and Screens . . . 149
701.11 Combustion Air Ducts. . . . . . . . . . 150
701.12 Dampers Prohibited . . . . . . . . . . . 150
702.0 Extra Device or Attachment . . . . . 150
702.1 General. . . . . . . . . . . . . . . . . . . . . 150
CHAPTER 8 CHIMNEYS AND VENTS. . . . . . . 151
801.0 General. . . . . . . . . . . . . . . . . . . . . 153
801.1 Applicability. . . . . . . . . . . . . . . . . . 153
801.2 Venting of Gas Appliances . . . . . . 153
801.3 Appliances Fueled by Other Fuels. 153
802.0 Venting of Appliances. . . . . . . . . . 153
xxxiv
CRC § 701.4 High relevance — show source text
701.4 Indoor Combustion Air . . . . . . . . . 147
701.5 Indoor Opening Size and Location . . . . . . . . . . . . . . . . . . . . 147
701.6 Outdoor Combustion Air . . . . . . . . 147
701.7 Combination Indoor and Outdoor
Combustion Air . . . . . . . . . . . . . . . 148
701.8 Engineered Installations . . . . . . . . 149
701.9 Mechanical Combustion Air
Supply. . . . . . . . . . . . . . . . . . . . . . 149
701.10 Louvers, Grilles, and Screens . . . 149
701.11 Combustion Air Ducts. . . . . . . . . . 150
701.12 Dampers Prohibited . . . . . . . . . . . 150
702.0 Extra Device or Attachment . . . . . 150
702.1 General. . . . . . . . . . . . . . . . . . . . . 150
CHAPTER 8 CHIMNEYS AND VENTS. . . . . . . 151
801.0 General. . . . . . . . . . . . . . . . . . . . . 153
801.1 Applicability. . . . . . . . . . . . . . . . . . 153
801.2 Venting of Gas Appliances . . . . . . 153
801.3 Appliances Fueled by Other Fuels. 153
802.0 Venting of Appliances. . . . . . . . . . 153
xxxiv
802.1 Listing . . . . . . . . . . . . . . . . . . . . . . 153
802.2 Connection to Venting Systems . . 153
802.3 Minimum Safe Performance . . . . . 153
802.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . . . . . . 154
802.5 Masonry, Metal, and Factory-Built Chimneys . . . . . . . . . . . . . . . . . . . 154
Table 802.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . . . . . . 155
802.6 Gas Vents. . . . . . . . . . . . . . . . . . . 157
Table 802.6.1 Roof Slope Heights. . . . . . . . . . . . 158
802.7 Single-Wall Metal Pipe . . . . . . . . . 159
Table 802.7.3.3 Clearance for Connectors. . . . . . . 160
802.8 Through-the-Wall Vent Termination . . . . . . . . . . . . . . . . . . 160
802.9 Condensation Drain . . . . . . . . . . . 160
802.10 Vent Connectors for Category I Appliances . . . . . . . . . . . . . . . . . . 160
Table 802.10.1.3 Minimum Thickness for Galvanized
Steel Vent Connectors for Low Heat Appliances . . . . . . . . . . . . . . 161
CRC § 101.2 High relevance — show source text
Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.2
COMBUSTIBLE CONSTRUCTION, CLOSED
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.0
COMBUSTIBLE CONSTRUCTION, OPEN
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217.0
COMBUSTIBLE MATERIAL
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.0
COMBUSTIBLE MATERIAL, LIMITED
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.0
COMBUSTION AIR
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.0
Duct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701.11, 701.12
General requirements . . . . . . . . . . . . . . . . . . Chapter 7
COMBUSTION AIR FOR
Boilers, low pressure,
installed in closets . . . . . . . . . . . . . . . . . . . . . . . 904.2
Engineered installations. . . . . . . . . . . . . . . . . . . . . 701.8
Fireplaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 912.4
Fossil fuel heating equipment. . . . . . . . . . . . . E 502.6.1
Furnaces, central heating . . . . . . . . . . . . . . 904.2, 907.4
COMBUSTION AIR FROM
Bedroom or bathroom. . . . . . . . . . . . . . . . . . . . . . 902.2
Chimneys and vents . . . . . . . . . . . . . . . . . . . 802.5.11.1
Combination, indoor and outdoor. . . . . . . 701.7, F 103.0
Indoors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701.4
Louvers, grilles and screens . . . . . . . . . . . . . . . . 701.10
Mechanical supply . . . . . . . . . . . . . . . . . . . . . . . . . 701.9
Outdoors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701.6
Refrigeration machinery rooms . . . . . . . . . . . . . . 1106.5
COMMERCIAL FOOD
HEAT-PROCESSING EQUIPMENT
CRC § 501.1 High relevance — show source text
Table 501.1(1) Water Heaters . . . . . . . . . . . . . . . .83
501.2 California Energy Code Water Heating System Requirements . . . . . . . . . . . . . . . . .83
502.0 Permits . . . . . . . . . . . . . . . . . . . . . .83
502.1 General . . . . . . . . . . . . . . . . . . . . . .83
503.0 Inspection . . . . . . . . . . . . . . . . . . . .83
503.1 Inspection of Chimneys or Vents . . .83
503.2 Final Water Heater Inspection . . . .83
504.0 Water Heater Requirements . . . . . .83
504.1 Location . . . . . . . . . . . . . . . . . . . . .83
Table 501.1(2) First Hour Rating . . . . . . . . . . . . . .83
504.2 Vent . . . . . . . . . . . . . . . . . . . . . . . .84
504.3 Clearance . . . . . . . . . . . . . . . . . . . .84
504.4 Pressure-Limiting Devices . . . . . . .84
504.5 Temperature-Limiting Devices . . . .84
504.6 Temperature, Pressure, and Vacuum Relief Devices . . . . . . . . .84
504.7 Lead Content . . . . . . . . . . . . . . . . .84
505.0 Oil-Burning and Other Water Heaters . . . . . . . . . . . . . . . . . . . . . .84
505.1 Water Heaters . . . . . . . . . . . . . . . .84
505.2 Safety Devices . . . . . . . . . . . . . . . .84
505.3 Oil-Fired Water Heaters . . . . . . . . .84
505.4 Indirect-Fired Water Heaters . . . . .84
506.0 Air for Combustion and
Ventilation . . . . . . . . . . . . . . . . . . . .84
506.1 General . . . . . . . . . . . . . . . . . . . . . .84
506.2 Indoor Combustion Air . . . . . . . . . .85
506.3 Indoor Opening Size and Location . . . . . . . . . . . . . . . . . . . . .85
506.4 Outdoor Combustion Air . . . . . . . . .85
506.5 Combination Indoor and
Outdoor Combustion Air . . . . . . . . .87
506.6 Engineered Installations . . . . . . . . .87
506.7 Mechanical Combustion Air Supply . . . . . . . . . . . . . . . . . . . . . . .87
506.8 Louvers, Grilles, and Screens . . . .87
506.9 Combustion Air Ducts . . . . . . . . . . .87
507.0 Appliance and Equipment Installation Requirements . . . . . . . .88
507.1 Dielectric Insulator . . . . . . . . . . . . .88
CRC § 203.0 High relevance — show source text
Readily, definition . . . . . . . . . . . . . . . . . . . . . . . . . 203.0
ACCESSORY DWELLING UNIT
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0
ADMINISTRATION
California . . . . . . . . . . . . . . . . . . . . Chapter 1, Division I
General . . . . . . . . . . . . . . . . . . . . . Chapter 1 , Division II
AIR
Balancing . . . . . . . . . . . . . 314.0, 403.10, 407.3, 511.3.1,
E 503.3.1, E 503.6.5.3,
E 605.1.5, E 803.2
Circulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407.4
Classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403.9
Combustion . . . . . . . . . . . . . . . . . (see Combustion Air)
Dilution . . . . . . . . . . . . . . . . . . . . . . . 203.0, Table 403.7,
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
CRC § 0.80 High relevance — show source text
(3) For the segment of the common vertical vent containing the offset, the common vent capacity listed in the common venting tables shall be reduced by 20 percent (0.80 x maximum common vent capacity).
(4) A multistory common vent shall not be reduced in size above the offset. [NFPA 54:13.2.17]
803.2.17 Vertical Vent Size Limitation. Where two
or more appliances are connected to a vertical vent or chimney, the flow area of the largest section of vertical vent or chimney shall not exceed seven times the smallest listed appliance categorized vent areas, flue collar area, or draft hood outlet area unless designed in accordance with engineering methods. [NFPA 54:13.2.18]
803.2.18 Two-Stage/Modulating Appliances. The minimum vent connector capacity (FAN Min) of appliances with more than one input rate shall be determined from the tables and shall be less than the lowest appliance input rating. The maximum vent connector capacity (FAN Max or NAT Max) shall be determined from the tables shall be greater than the highest appliance input rating. [NFPA 54:13.2.19]
803.2.19 Corrugated Metallic Chimney Liner Reduction. Listed corrugated metallic chimney liner systems in masonry chimneys shall be sized by using Table 803.2(1) or Table 803.2(2) for Type B vents, with the maximum capacity reduced by 20 percent (0.80 x maximum capacity) and the minimum capacity as shown in Table 803.2(1) or Table 803.2(2). Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Section 803.2.4 and Section 803.2.5. The 20 percent reduction for corrugated metallic chimney liner systems includes an allowance for one long radius 90 degree (1.57 rad) turn at the bottom of the liner. [NFPA 54:13.2.20]
803.2.20 Chimneys and Vents. Table 803.2(1) through Table 803.2(5) shall be used only for chimneys and vents not exposed to the outdoors below the roof line. A Type B vent or listed chimney lining system passing through an unused masonry chimney flue shall not be considered to be exposed to the outdoors. A Type B vent passing through an unventilated enclosure or chase
insulated to a value of not less than R8 shall not be con sidered to be exposed to the outdoors. Where vents extend outdoors above the roof more than 5 feet (1524 mm) higher than required by Table 802.6.1, and where vents terminate in accordance with Section 802.6.1(1)(b), the outdoor portion of the vent shall be enclosed as required by this section for vents not considered to be exposed to the outdoors, or such venting system shall be engineered. Table 803.2(6) through Table 803.2(9) shall be used for clay tile lined exterior masonry chimneys, provided all the following conditions are met:
(1) The vent connector is Type B double wall.
(2) At least one appliance is draft hood equipped.
(3) The combined appliance input rating is less than the maximum capacity given by Table 803.2(6) (for NAT+NAT) or Table 803.2(8) (for FAN+NAT).
CRC § 1009.1 High relevance — show source text
1009.1 Moving walk 1003.7 Number 1001.2, 1006 Occupant load 1004 Parking 406.5.7 Protruding objects 1003.3, 1005.7 Ramps 1012, 1019, 1027 Scoping 101.3, 108.2, 1001.1 Seating, fixed 1009.1, 1030 Special amusement areas 411.4 Stages 410.2.3, 410.5 Stairways 403.5, 404.6, 1005.3.1, 1011, 1019, 1023, 1027 Temporary structures 3103.4 Travel distance (see Travel Distance) 1006.2.1,
1017
Turnstile 1010.5
Underground buildings 405.5.1, 405.7 Width 1005.1, 1005.2, 1005.4, 1011.2, 1012.5.1, 1020.3, 1030.6, 1030.8 Mechanical (see Air Conditioning, Heating, Refrigeration and Ventilation) 101.4.2 Access 1011.12, 1208.4 Air transfer openings 705.11, 706.11, 707.10, 708.9, 709.8, 712.1.6, 713.10, 714.1.1, 717 Chimneys (see Chimneys) Code Chapter 28 Disconnected 3303.6
Ducts 704.7, 705.11, 706.11, 707.10, 708.9, 709.8, 710.8, 712.1.10.3, 712.1.6, 713.10, 714.1.1, 717 Encroachment, public right-of-way 3202.3.2 Equipment on roof 1511 Equipment platforms 505.3 Fireplaces 2111 Incidental use room Table 509.1
Motion picture projection room 409.3 Permit required 105.1, 105.2 Roof access 1011.12 Seismic inspection and testing 1704.3.2, 1705.13.7 Smoke control system 909 Systems Chapter 28 Mechanically Laminated Decking 2304.9.3 Medical Care (see Institutional I-2) 407.1 Medical Gas Systems 427 Membrane Roof Coverings 1507.11, 1507.12, 1507.13 Membrane Structures 2702.2, 3102 Mercantile Occupancy (Group M) 309 Accessible Chapter 11B Alarm and detection 907.2.6.3.4
Area 503, 505, 506, 507, 508 Covered and open mall buildings 402 Hazardous material display and storage 414.2.5 Height 503, 504, 505, 508 Incidental uses 509
CRC § 9.2.2 High relevance — show source text
Entire Chapter||||||||||||||||||||||||| |Adopt Entire Chapter as
amended (amended sections
listed below)||||||||||||||||||||||||| |Adopt only those sections
that are listed below|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| |Chapter/Section||||||||||||||||||||||||| |1.9.2.2 & 1.9.2.2.1|||||||||X|||||||||||||||| |1.10.1 and subsections||||||||||X|X|||||||||||||| |1.10.2 and subsections||||||||||||X||||||||||||| |1.10.3 and subsections|||||||||||||X|||||||||||| |1.10.4 and subsections||||||||||||||X||||||||||| |1.10.5 and subsections|||||||||||||||X|||||||||| |1.10.6 and subsections||||||||||||||||X||||||||| |1.11.0 through 1.11.11|||X|||||||||||||||||||||| |1.12.0|||||||||||||||||||||||X|| |1.13.0||||||||||||||||||||X||||| |1.14.0||||||||||||||||||||||||X| |Division II –
Scope and Administration||||||||||||||||||||||||| |101.0 – 104.1||||||||||X|X|X|X|X|X|||||||||| |104.2 (Items 1 – 5)||||X|X|||||||||||||||||||| |104.3 – 107.0||||||||||X|X|X|X|X|X|||||||||| |104.4.3.1|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.
2 2025 CALIFORNIA MECHANICAL CODE
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CHAPTER 1
ADMINISTRATION
DIVISION I CALIFORNIA ADMINISTRATION
1.1.0 General.
CRC § 9.3.8.7 High relevance — show source text
Exception: Direct vent appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:9.3.8.7]
(8) Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located at least 12 inches (305 mm) vertically from the adjoining finished ground level.
[NFPA 54:9.3.8.8]
701.12 Dampers Prohibited. Combustion air ducts or plenums shall not be installed so as to require openings in or penetrations through construction where fire dampers are required. Manually operated dampers shall not be installed in combustion air openings. With prior approval, power-actuated movable louvers admitting combustion air shall be permitted to be used and, where installed, shall be electrically interlocked with the main burner fuel-supply valve so as to prevent fuel delivery unless the louvers are in the fully open position.
702.0 Extra Device or Attachment.
702.1 General. No device or attachment shall be installed on any appliance that could in any way impair the combustion of gas. [NFPA 54:9.1.15]
150 2025 CALIFORNIA MECHANICAL CODE
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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE
CHAPTER 8 – CHIMNEYS AND VENTS
(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 X X X X X X X X X Adopt Entire Chapter as
amended (amended sections
listed below)Adopt only those sections
that are listed belowChapter/Section CRC § 12-0 High relevance — show source text
000|DR|DR|12-0|15-3|10-11|15-0|10-2|14-8| |8|2-#4
1-#6|60,000|DR|DR|DR|DR|12-2|15-3|11-7|15-3| |8|2-#5|40,000|DR|DR|DR|DR|12-7|16-7|11-9|16-7| |8|2-#5|60,000|DR|DR|DR|DR|DR|DR|13-3|16-7| |8|2-#6|40,000|DR|DR|DR|DR|DR|DR|13-2|17-8| |8|2-#6|60,000|DR|DR|DR|DR|DR|DR|DR|DR| |12|1-#4|40,000|11-5|9-10|10-6|12-0|9-6|11-6|8-9|11-1| |12|1-#4|60,000|11-5|9-10|11-8|13-3|10-11|14-0|10-1|13-6| |12|1-#5|40,000|11-5|9-10|11-8|13-3|11-1|14-4|10-3|13-9| |12|1-#5|60,000|11-5|9-10|11-8|13-3|11-10|16-0|11-9|16-9| |12|2-#4
1-#6|40,000|DR|DR|11-8|13-3|11-10|16-0|11-2|15-6| |12|2-#4
1-#6|60,000|DR|DR|11-8|13-3|11-10|16-0|11-11|18-4| |12|2-#5|40,000|DR|DR|11-8|13-3|11-10|16-0|11-11|18-4| |12|2-#5|60,000|DR|DR|11-8|13-3|11-10|16-0|11-11|18-4| |16|1-#4|40,000|13-6|13-0|11-10|13-8|10-7|12-11|9-11|12-4| |16|1-#4|60,000|13-6|13-0|13-8|16-7|12-4|15-9|11-5|15-0| |16|1-#5|40,000|13-6|13-0|13-10|17-0|12-6|16-1|11-7|15-4| |16|1-#5|60,000|13-6|13-0|13-10|17-1|14-0|19-7|13-4|18-8| |16|2-#4
1-#6|40,000|13-6|13-0|13-10|17-1|13-8|18-2|12-8|17-4| |16|2-#4
1-#6|60,CRC § 8-8 High relevance — show source text
000|8-8|9-10|6-7|7-0|5-11|5-2|4-8|3-9|3-7| |12i|2-#4
1-#6|60,000|8-8|10-1|6-7|7-0|5-11|5-2|4-8|3-9|3-7| |12i|Center distance_A_m, n|Center distance_A_m, n|1-2|1-5|0-10|0-11|0-9|0-7|0-6|STL|STL| |16i|Span without stirrupsk, l|Span without stirrupsk, l|3-10|4-3|3-6|3-7|3-4|3-2|3-0|2-10|2-9| |16i|1-#4|40,000|6-5|7-2|5-6|5-9|5-2|4-8|4-4|3-7|3-6| |16i|1-#4|60,000|7-9|8-9|6-9|7-0|6-3|5-8|5-3|4-4|4-3| |16i|1-#5|40,000|7-11|8-11|6-10|7-1|6-5|5-9|5-4|4-5|4-4| |16i|1-#5|60,000|9-8|10-11|8-4|8-8|7-10|7-0|6-6|5-2|5-1| |16i|2-#4
1-#6|40,000|9-0|10-1|7-9|8-0|7-3|6-6|6-1|5-0|4-11| |16i|2-#4
1-#6|60,000|11-5|13-10|9-2|9-8|8-3|7-2|6-6|5-2|5-1| |16i|Center distance_A_m, n|Center distance_A_m, n|1-6|1-11|1-2|1-3|1-0|0-10|0-8|STL|STL| |20i|Span without stirrupsk, l|Span without stirrupsk, l|4-10|5-5|4-5|4-7|4-3|4-0|3-11|3-7|3-7| |20i|1-#4|40,000|7-0|8-1|6-3|6-5|5-10|5-3|4-11|4-1|3-11| |20i|1-#4|60,000|8-7|9-10|7-7|7-10|7-1|6-5|6-0|4-11|4-10| |20i|1-#5|40,000|8-9|10-1|7-9|8-0|7-3|6-6|6-1|5-1|4-11| |20i|1-#5|60,CRC § 2.25 Medium relevance — show source text
00|2.25|0.70|DR|3.70|1.05|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|33 mil cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|16|3.85|1.45|DR|DR|3.40|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|33 mil cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|24|3.40|DR|DR|DR|2.70|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|12|3.00|1.80|DR|DR|3.00|0.65|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|16|3.00|1.00|DR|DR|2.85|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|24|2.85|DR|DR|DR|2.20|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|12|4.00|3.85|2.80|1.80|4.00|3.05|1.50|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|16|4.00|3.30|1.95|0.60|4.00|2.25|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|24|4.00|2.25|DR|DR|4.00|0.65|DR|DR| |For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
DR = Design Required, o.c. = on center.
a. Wood furring shall be spruce-pine-fir or any softwood species with a specific gravity of 0.42 or greater.CRC § 1002.2 Medium relevance — show source text
Evacuation plans 1002.2 Existing buildings 3310 Exit (see Exit) 1022, 1027 Exit access (see Exit Access) 1016, 1021 Exit discharge (see Exit Discharge) 1028 Exit enclosures 1023.2
Exit passageway 1024 Exit signs 1013, 2702.2 Fire escapes 412.7.3 Fire safety plans 1002.2 Floor surface 804, 1003.4 Gates 1010.4
Group I-2 407.2, 407.3, 407.4, 1019.4 Group I-3 408.2, 408.3, 408.4, 408.6, 408.8, 1019.4 Guards 1015
Handrails 1014
Hazardous materials 414.6.1.2, 415.11.2, 415.11.6.6 Headroom 1003.2, 1003.3 Heliports, Helistops 412.7.3 High-hazard Group H 415.11.2 High-rise 403.5, 403.6 Illumination 1008, 2702.2 Interior finish 803.13, 804 Ladders (see Ladders) Live loads Table 1607.1
Live/work units 508.5.3 Mezzanines 505.2.2, 505.2.3, 1004.2.2,
1009.1 Moving walk 1003.7 Number 1001.2, 1006 Occupant load 1004 Parking 406.5.7 Protruding objects 1003.3, 1005.7 Ramps 1012, 1019, 1027 Scoping 101.3, 108.2, 1001.1 Seating, fixed 1009.1, 1030 Special amusement areas 411.4 Stages 410.2.3, 410.5 Stairways 403.5, 404.6, 1005.3.1, 1011, 1019, 1023, 1027 Temporary structures 3103.4 Travel distance (see Travel Distance) 1006.2.1,
1017
Turnstile 1010.5
Underground buildings 405.5.1, 405.7 Width 1005.1, 1005.2, 1005.4, 1011.2, 1012.5.1, 1020.3, 1030.6, 1030.8 Mechanical (see Air Conditioning, Heating, Refrigeration and Ventilation) 101.4.2 Access 1011.12, 1208.4 Air transfer openings 705.11, 706.11, 707.10, 708.9, 709.8, 712.1.6, 713.10, 714.1.1, 717 Chimneys (see Chimneys) Code Chapter 28 Disconnected 3303.6
CRC § 2-16 Medium relevance — show source text
Stud to top or bottom plate|2-16d common (31/2″ × 0.162″); or
3-16d box (31/2″ x 0.135″); or
3-10d box (3″ × 0.128″); or
3-3″ × 0.131″ nails; or
3-3″ 14 gage staples,7/16″ crown|End nail| |17. Top plates, laps at corners and intersections|2-16d common (31/2″ × 0.162″); or
3-10d box (3″ × 0.128″); or
3-3″ × 0.131″ nails; or
3-3″ 14 gage staples,7/16″ crown|Face nail| |18. 1″ brace to each stud and plate|3-8d box (21/2″ x 0.113″); or
2-8d common (21/2″ × 0.131″); or
2-10d box (3″ × 0.128″); or
2-3″ × 0.131″ nails; or
2-3″ 14 gage staples,7/16″ crown|Face nail| |19. 1″ × 6″ sheathing to each bearing|3-8d box (21/2″ x 0.113″); or
2-8d common (21/2″ × 0.131″); or
2-10d box (3″ × 0.128″); or
2-13/4″ 16 gage staples, 1″ crown|Face nail| |20. 1″ × 8″ and wider sheathing to each bearing|3-8d common (21/2″ × 0.131″); or
3-8d box (21/2″ x 0.113″); or
3-10d box (3″ × 0.128″); or
3-13/4″ 16 gage staples, 1″ crown|Face nail| |20. 1″ × 8″ and wider sheathing to each bearing|Wider than 1″ × 8″
3-8d common (21/2″ x 0.131″); or
4-8d box (21/2″ × 0.113″); or
3-10d box (3″ × 0.128″); or
4-13/4″ 16 gage staples, 1″ crown|Wider than 1″ × 8″
3-8d common (21/2″ x 0.131″); or
4-8d box (21/2″ × 0.113″); or
3-10d box (3″ × 0.128″); or
4-13/4″ 16 gage staples, 1″ crown| |Floor|Floor|Floor| |21.CRC § 9.3.7.1 Medium relevance — show source text
Where the free area through a design of louver, grille, or screen is known, it shall be used in calculating the size opening required to provide the free area specified. Where the louver and grille design and free area are not known, it shall be assumed that wood louvers have 25 percent free area and metal louvers and grilles have 75 percent free area. Nonmotorized louvers and grilles shall be fixed in the open position. [NFPA 54:9.3.7.1]
701.10.1 Minimum Screen Mesh Size. Screens shall not be smaller than [1] ⁄ 4 of an inch (6.4 mm) mesh. [NFPA 54:9.3.7.2]
701.10.2 Motorized Louvers. Motorized louvers shall be interlocked with the appliance so they are proven in the full open position prior to main burner ignition and during main burner operation. Means shall be provided to prevent the main burner from igniting should the louver fail to open during burner startup and to shut down the main burner if the louvers close during burner operation.
[NFPA 54:9.3.7.3]
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COMBUSTION AIR
701.11 Combustion Air Ducts. Combustion air ducts shall comply with the following [NFPA 54:9.3.8]:
(1) Ducts shall be constructed of galvanized steel or a material having equivalent corrosion resistance, strength, and rigidity.
Exception: Within dwellings units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than one fireblock is removed. [NFPA 54:9.3.8.1]
(2) Ducts shall terminate in an unobstructed space, allowing free movement of combustion air to the appliances.
[NFPA 54:9.3.8.2]
(3) Ducts shall serve a single space. [NFPA 54:9.3.8.3]
(4) Ducts shall not serve both upper and lower combustion air openings where both such openings are used. The separation between ducts serving upper and lower combustion air openings shall be maintained to the source of combustion air. [NFPA 54:9.3.8.4]
(5) Ducts shall not be screened where terminating in an attic space. [NFPA 54:9.3.8.5]
(6) Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air. [NFPA 54:9.3.8.6]
(7) The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory built chimney shall not be used to supply combustion air.
Exception: Direct vent appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:9.3.8.7]
(8) Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located at least 12 inches (305 mm) vertically from the adjoining finished ground level.
CRC § 9.3.8.1 Medium relevance — show source text
Exception: Within dwellings units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than one fireblock is removed. [NFPA 54:9.3.8.1]
(2) Ducts shall terminate in an unobstructed space, allowing free movement of combustion air to the appliances.
[NFPA 54:9.3.8.2]
(3) Ducts shall serve a single space. [NFPA 54:9.3.8.3]
(4) Ducts shall not serve both upper and lower combustion air openings where both such openings are used. The separation between ducts serving upper and lower combustion air openings shall be maintained to the source of combustion air. [NFPA 54:9.3.8.4]
(5) Ducts shall not be screened where terminating in an attic space. [NFPA 54:9.3.8.5]
(6) Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air. [NFPA 54:9.3.8.6]
(7) The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory built chimney shall not be used to supply combustion air.
Exception: Direct vent appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:9.3.8.7]
(8) Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located at least 12 inches (305 mm) vertically from the adjoining finished ground level.
[NFPA 54:9.3.8.8]
701.12 Dampers Prohibited. Combustion air ducts or plenums shall not be installed so as to require openings in or penetrations through construction where fire dampers are required. Manually operated dampers shall not be installed in combustion air openings. With prior approval, power-actuated movable louvers admitting combustion air shall be permitted to be used and, where installed, shall be electrically interlocked with the main burner fuel-supply valve so as to prevent fuel delivery unless the louvers are in the fully open position.
702.0 Extra Device or Attachment.
702.1 General. No device or attachment shall be installed on any appliance that could in any way impair the combustion of gas. [NFPA 54:9.1.15]
150 2025 CALIFORNIA MECHANICAL CODE
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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE
CHAPTER 8 – CHIMNEYS AND VENTS
(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.)
CRC § 140.9 Medium relevance — show source text
9(c)3B Fume Hood Intensive Laboratories 140.9(c)4, Table 140.9-D Function 110.2(a)3, 110.9(b)1D, 110.12(a), 110.12(c)1, 120.8(b)3, 120.8(f)4, 130.1(c)6D, 130.1(f), 141.0(b)2I, 160.5(b)4C, 160.5(b)4F, 180.3(b)4B Function Areas 120.6(g)1, 120.8, 130.1(c)1C, 130.1(c)3B, 130.1(c), 140.6(a)3D, 140.6(c)2AB, 140.6(c)2G, 140.6(c)3A, 140.6(c)3F, 140.6(c)3, 170.2(e)4 Functional Areas 160.5, 130.0(b) Functional Performance Testing 120.8(a)6, 120.8(g) Furnace Installation 150.0(h)4A, 160.3(b)4A Furnace Output 150.0(h)1 Future 240V Use 150.0(n)1, 150.0(t)2, 150.0(u)2, 150.0(v)2, 160.4(a)1B, 160.9(a)2, 160.9(b)2, 160.9(c)
G
Gas Bypass 140.4(e)3B, 170.2(c)4C Cooler efficiency 120.6(a)8H, 120.6(b)5H Cooler pressure 120.6(a)8E-F, 120.6(b)5E-F Fired furnace 110.2(d), Table 110.2-I, Table 110.2-J Furnace 150.0(m)13, 150.1(c)10, 160.3(b)5L, 170.2(c)3B Heater 110.4(b)2 Log 150.0(e), 160.1(f) Or propane 100.2, 150.0(n)1, 150.0(t-v), 150.1(c)8, 150.2(a)1D, 150.2(b)1H, 160.4(a), 160.9, 170.2(d)1C, 170.2(d)3, 180.2(b)3C Service water heating 140.5(c), 141.0(a)2, 170.2(d)3A Supply 160.4(a)4 Water heater 140.5(c), 150.0(n), 170.2(d)3 Gas- and Oil-fired Boilers, Minimum Efficiency Requirements Table 110.2-J Gasket 110.7, 120.1(c)1D, 150.0(a)3, 150.0(k)1C, 150.0(m)12B, 160.1(a)1B, 160.2(b)1B, 160.2(c)1D, 160.5(a)1C Geometry 140.3(a)6E, 141.0(b)3D2, 150.
CRC § 506.8 Medium relevance — show source text
506.8 Louvers, Grilles, and Screens. The required size of openings for combustion, ventilation, and dilution air shall be based on the net free area of each opening. Where the free area through a design of louver, grille, or screen is known, it shall be used in calculating the size opening required to provide the free area specified. Where the louver and grille design and free area are not known, it shall be assumed that wood louvers have 25 percent free area, and metal louvers and grilles have 75 percent free area. Nonmotorized louvers and grilles shall be fixed in the open position. [NFPA 54:9.3.7.1]
506.8.1 Minimum Screen Mesh Size. Screens shall not be smaller than [1] ⁄ 4 of an inch (6.4 mm) mesh. [NFPA 54:9.3.7.2]
506.8.2 Motorized Louvers. Motorized louvers shall be interlocked with the appliance so they are proven in the full open position prior to main burner ignition and during main burner operation. Means shall be provided to prevent the main burner from igniting should the louver fail to open during burner startup and to shut down the main burner if the louvers close during burner operation.
[NFPA 54:9.3.7.3]
506.9 Combustion Air Ducts. Combustion air ducts shall comply with the following [NFPA 54:9.3.8]:
(1) Ducts shall be constructed of galvanized steel or a material having equivalent corrosion resistance, strength, and rigidity.
Exception: Within dwellings units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than one fireblock is removed. [NFPA 54:9.3.8.1]
2025 CALIFORNIA PLUMBING CODE 87
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WATER HEATERS
(2) Ducts shall terminate in an unobstructed space, allowing free movement of combustion air to the appliances.
[NFPA 54:9.3.8.2]
(3) Ducts shall serve a single space. [NFPA 54:9.3.8.3]
(4) Ducts shall not serve both upper and lower combustion air openings where both such openings are used. The separation between ducts serving upper and lower combustion air openings shall be maintained to the source of combustion air. [NFPA 54:9.3.8.4]
(5) Ducts shall not be screened where terminating in an attic space. [NFPA 54:9.3.8.5]
(6) Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located at least 12 inches (305 mm) vertically from the adjoining finished ground level.
[NFPA 54:9.3.8.8]
(7) Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air. [NFPA 54:9.3.8.6]
CRC § 7-1 Medium relevance — show source text
d.: Replace Table 7-1, 8-1, 8-2, or 9-1 with Table 4-A.
(5) ASHRAE 170. Section 6.9 -- See also Section 605.2 and 605.3.
(6) ASHRAE 170. Section 7.1a -- Modify as follows:
Replace reference to Table 7-1 with reference to Table 4-A.
(7) ASHRAE 170. Section 7.2.1 c -- Not adopted.
(8) ASHRAE 170. Section 7.2.2 Also see Section 415.0.
(9) ASHRAE 170. Section 7.2.3 -- Not adopted.
(10)ASHRAE 170. Section 7.3.1 -- Modify as follows:
Replace reference to Table 7-1 with reference to Table 4-A.
(11) ASHRAE 170. Section 7.4.1 -- Modify as follows:
Delete the Exception that allows for high return grilles.
(12)ASHRAE 170. Section 8.1a -- Modify as follows: Replace reference to Table 8-1 with reference to Table 4-A.
(13)ASHRAE 170. Section 8.2 -- Modify as follows: Replace reference to Table 8-2 with reference to Table 4-A.
(14)ASHRAE 170. Section 9.1a -- Modify as follows: Replace reference to Table 9-1 with reference to Table 4-A.
2025 CALIFORNIA MECHANICAL CODE 69
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VENTILATION AIR
«
«
402.2.1.5 Corner Openings. For zones with operable openings on two adjacent sides of a zone, the distance from the operable openings shall be not more than 5 H along a line drawn between the two openings that are farthest apart. Floor area outside that line shall comply with Section 402.2.1.1 as a zone having openings on only one side of the zone.
[ASHRAE 62.1:6.4.1.5]
402.2.1.6 Location and Size of Openings. Zones or portions of zones to be naturally ventilated shall have a permanently open airflow path to openings directly connected to the outdoors. The minimum flow rate to the zone shall be determined in accordance with
Section 403.2.1. This flow rate shall be used to deter mine the required openable area of openings, accounting only for buoyancy-driven flow. Wind-driven flow shall be used only where it can be demonstrated that the minimum flow rate is provided during all occupied hours. Openings shall be sized in accordance with Section 402.2.1.6(A). Permanently open airflow path shall include, but not be limited to, pathways that would allow airflow unimpeded by partitions, walls, and furnishings. {ASHRAE 62.1:6.4.1.6}
CRC § 25.4 Medium relevance — show source text
WOOD MANTEL
MASONRY
COMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
2″ CLEAR
TO COMB
FRAME WCOMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
2″ CLEAR
TO COMBCol3 COMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
MASONRY
2″ CLEAR
TO COMB
FRAME WFor SI: 1 inch = 25.4 mm
2111 A .13 Fireplace fireblocking. All spaces between fireplaces and floors and ceilings through which fireplaces pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be to a depth of 1 inch (25 mm) and shall only be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.
2111 A .14 Exterior air. Factory-built or masonry fireplaces covered in this section shall be equipped with an exterior air supply to ensure proper fuel combustion unless the room is mechanically ventilated and controlled so that the indoor pressure is neutral or positive.
2111 A .14.1 Factory-built fireplaces. Exterior combustion air ducts for factory-built fireplaces shall be listed components of the fireplace, and installed according to the fireplace manufacturer’s instructions.
21A-12 2025 CALIFORNIA BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MASONRY
2111 A .14.2 Masonry fireplaces. Listed combustion air ducts for masonry fireplaces shall be installed according to the terms of their listing and manufacturer’s instructions.
2111 A .14.3 Exterior air intake. The exterior air intake shall be capable of providing all combustion air from the exterior of the dwelling. The exterior air intake shall not be located within a garage, attic, basement or crawl space of the dwelling nor shall the air intake be located at an elevation higher than the firebox. The exterior air intake shall be covered with a corrosion-resistant screen of [1] / 4 -inch (6.4 mm) mesh.
2111 A .14.4 Clearance. Unlisted combustion air ducts shall be installed with a minimum 1-inch (25 mm) clearance to combustibles for all parts of the duct within 5 feet (1524 mm) of the duct outlet. 2111 A .14.5 Passageway. The combustion air passageway shall be not less than 6 square inches (3870 mm [2] ) and not more than 55 square inches (0.035 m [2] ), except that combustion air systems for listed fireplaces or for fireplaces tested for emissions shall be constructed according to the fireplace manufacturer’s instructions.
2111 A .14.6 Outlet. The exterior air outlet is permitted to be located in the back or sides of the firebox chamber or within 24 inches (610 mm) of the firebox opening on or near the floor. The outlet shall be closable and designed to prevent burning material from dropping into concealed combustible spaces.
SECTION 2112 A —MASONRY HEATERS
CRC § 25.4 Medium relevance — show source text
2 ″ CLEARANCE (AIRSPACE) TO COMBUSTIBLE FRAMING
For SI: 1 inch = 25.4 mm
2111.13 Fireplace fireblocking. All spaces between fireplaces and floors and ceilings through which fireplaces pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be to a depth of 1 inch (25 mm) and shall only be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.
2111.14 Exterior air. Factory-built or masonry fireplaces covered in this section shall be equipped with an exterior air supply to ensure proper fuel combustion unless the room is mechanically ventilated and controlled so that the indoor pressure is neutral or positive.
2111.14.1 Factory-built fireplaces. Exterior combustion air ducts for factory-built fireplaces shall be listed components of the fireplace, and installed according to the fireplace manufacturer’s instructions.
MASONRY
COMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
2″ CLEAR
TO COMB
FRAME W
WOOD MANT
spaces between fireplaces and floors and
al securely fastened in place. The fireblock
nd shall only be placed on strips of metal
r masonry fireplaces covered in this sect
s the room is mechanically ventilated an
es. Exterior combustion air ducts for fact
o the fireplace manufacturer’s instructionCOMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
2″ CLEAR
TO COMBCol3 spaces between fireplaces and floors and
al securely fastened in place. The fireblock
nd shall only be placed on strips of metal
r masonry fireplaces covered in this sect
s the room is mechanically ventilated an
es. Exterior combustion air ducts for fact
o the fireplace manufacturer’s instruction
COMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
MASONRY
2″ CLEAR
TO COMB
FRAME W
WOOD MANT2111.14.2 Masonry fireplaces. Listed combustion air ducts for masonry fireplaces shall be installed according to the terms of their listing and manufacturer’s instructions.
2111.14.3 Exterior air intake. The exterior air intake shall be capable of providing all combustion air from the exterior of the dwelling. The exterior air intake shall not be located within a garage, attic, basement or crawl space of the dwelling nor shall the air intake be located at an elevation higher than the firebox. The exterior air intake shall be covered with a corrosion-resistant screen of [1] / 4 -inch (6.4 mm) mesh.
2111.14.4 Clearance. Unlisted combustion air ducts shall be installed with a minimum 1-inch (25 mm) clearance to combustibles for all parts of the duct within 5 feet (1524 mm) of the duct outlet. 2111.14.5 Passageway. The combustion air passageway shall be not less than 6 square inches (3870 mm [2] ) and not more than 55 square inches (0.035 m [2] ), except that combustion air systems for listed fireplaces or for fireplaces tested for emissions shall be constructed according to the fireplace manufacturer’s instructions.
CRC § 9.3.8.8 Medium relevance — show source text
(6) Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located at least 12 inches (305 mm) vertically from the adjoining finished ground level.
[NFPA 54:9.3.8.8]
(7) Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air. [NFPA 54:9.3.8.6]
(8) The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory built chimney shall not be used to supply combustion air.
Exception: Direct-vent appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:9.3.8.7]
507.0 Appliance and Equipment Installation Require- ments.
507.1 Dielectric Insulator. The Authority Having Jurisdiction shall have the authority to require the use of an approved dielectric insulator on the water piping connections of water heaters and related water heating appliances.
507.2 Seismic Provisions. Water heaters shall be anchored or strapped to resist horizontal displacement due to earthquake motion. Strapping shall be at points within the upper one-third ( [1] ∕ 3 ) and lower one-third ( [1] ∕ 3 ) of its vertical dimensions. At the lower point, minimum a distance of not less than four ( 4 ) inches (102 mm) shall be maintained above the controls with the strapping. Note: [HCD 1 & HCD 2] Reference Health and Safety Code Section 19211(a) which addresses new, replacement, and existing water heaters. Note: The applicable subsection of Health and Safety Code Sec- tion 19211(a) which addresses new, replacement, and existing water heaters is repeated here for clarity and reads as follows: Section 19211(a) Notwithstanding Section 19100, all new and replacement water heaters, and all existing residential water heaters shall be braced, anchored, or strapped to resist falling or horizontal displacement due to earthquake motion. At a minimum, any water heater shall be secured in accor- dance with the California Plumbing Code, or modifications made thereto by a city, county, or city and county pursuant to Section 17958.5.
507.3 Appliance Support. Appliances and equipment shall be furnished either with load distributing bases or with a suf
ficient number of supports to prevent damage to either the building structure or the appliance and the equipment. [NFPA 54:9.1.8.1] 507.3.1 Structural Capacity. At the locations selected for installation of appliances and equipment, the dynamic and static load carrying capacities of the building structure shall be checked to determine whether they are adequate to carry the additional loads. The appliances and equipment shall be supported and shall be connected to the piping so as not to exert undue stress on the connections. [NFPA 54:9.1.8.2] 507.4 Ground Support. A water heater supported from the earth shall rest on level concrete or other approved base extending not less than 3 inches (76 mm) above the adjoining ground level. **507.5 Drainage Pan.
CRC § 1901.2.1 Medium relevance — show source text
1901.2.1
D8223—19: Standard Practice for Evaluation of Fire-Retardant Treated Laminated Veneer Lumber
2303.2.6.3
D8257/D8257M—20: Standard Specification for Mechanically Attached Polymeric Roof Underlayment Used in Steep Slope Roofing 1507.1.1, Table 1507.1.1(1)
E84—21a: Standard Test Methods for Surface Burning Characteristics of Building Materials
202, 402.6.4.4, 406.7.2, 424.2, 602.4.1.1, 602.4.2.1, 602.4.3.1, 720.1, 720.4, 803.1.2, 803.5.2, 803.10, 803.11, 803.12, 803.13, 806.6, 1402.6, 1403.11.1, 1406.9, 1406.10.1, 1408.9, 1408.10.1, 1511.6.2, 1511.6.3, 2303.2, 2603.3, 2603.4.1.13, 2603.5.4, 2603.5.5, 2603.7, 2604.2.4, 2606.4, 2612.3, 2614.3, 3105.3
E90—2009(2016): Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements
1206.2, 1206.2.1
E96/E96M—21: Standard Test Methods for Gravimetric Determination of Water Vapor Transmission Rate of Materials
202, 1202.3, 1404.3
E108—20a: Standard Test Methods for Fire Tests of Roof Coverings
1505.1, 2603.6, 2610.2, 2610.3
E119—20: Standard Test Methods for Fire Tests of Building Construction and Materials
705.8.5, 703.2.1.1, 703.2.1.3, 703.2.1.4, 703.2.1.5, 703.2.2, 703.4, 703.6, 704.11, 705.8, 707.6, 712.1.13.2, 714.4.1, 714.5.1, 715.3, 715.4, 715.4.1, Table 716.1(1), Table 716.1(2), Table 716.1(3), 716.1.2.3, 716.2.5.1.1, 716.2.5.4, 716.3.2.1.1, 717.3.1, 717.5.2, 717.5.3, 717.6.1, 717.6.2, Table 721.1(1), 2103.1, 2603.5.1
E136—2022: Standard Test Method for Assessing Combustibility of Materials Using a Vertical Tube Furnace at 750 Degrees C
703.3.1
CRC § 1003.2.1 Medium relevance — show source text
Required|Per
NFPA
85|Per
NFPA 85| |SAFETY CONTROL TIMING
(NOMINAL MAXIMUM TIME IN SECONDS)|TRIAL FOR MAIN
BURNER FRAME|DIRECT
ELECTRIC
IGNITION|Not
Required|15|15|15|90|30|15|15|Not
Required|Per
NFPA 85|Per
NFPA 85| |SAFETY CONTROL TIMING
(NOMINAL MAXIMUM TIME IN SECONDS)|TRIAL FOR
PILOT|TRIAL FOR
PILOT|90|15|15|15|Not
Required|Not
Required|Not
Required|15|Not
Required|10 sec
Per
NFPA 85|Per
NFPA 85| |TYPE OF
PILOT2|TYPE OF
PILOT2|TYPE OF
PILOT2|Any type|Interrupted
or
Intermittent|Interrupted
or
Intermittent|Interrupted|Any type|Interrupted|Interrupted|Interrupted|Not required|Any|None| |FUEL INPUT
RANGE1
(INCLUSIVE),
BTU/H|FUEL INPUT
RANGE1
(INCLUSIVE),
BTU/H|FUEL INPUT
RANGE1
(INCLUSIVE),
BTU/H|0 - 400 000|400 001 -
2 500 000|2 500 001 -
5 000 000|Over
5 000 000|0 - 400 000|400 001 -
1 000 000|1 000 001 -
3 000 000|Over
3 000 000|All|12 500 000
or more|Any| |FUEL|FUEL|FUEL|Gas|Gas|Gas|Gas|Oil|Oil|Oil|Oil|Electric|Gas, Oil
and/or
Coal|Heat
Recovery
Steam
Generator| |BOILER
GROUP|BOILER
GROUP|BOILER
GROUP|A|B|C|D|E|F|G|H|K|L|M|222 2025 CALIFORNIA MECHANICAL CODE
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BOILERS AND PRESSURE VESSELS
FOOTNOTES FOR TABLE 1003.2.1 (continued)
1 Fuel input shall be determined by one of the following:
The burner input shall not exceed the input shown on the burner nameplate or as otherwise identified by the manufacturer.
The nominal boiler rating, as determined by the building official, plus 25 percent.
2 Automatic boilers shall have one flame failure device on each burner, which shall prove the presence of an ignition source at the point where it will ignite
CRC § 36-3 Medium relevance — show source text
CHAPTER 36 MARINAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-3
3601 Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-3 3602 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-3
3603 General Precautions. . . . . . . . . . . . . . . . . . . . . . . . . . . 36-3
3604 Fire Protection Equipment . . . . . . . . . . . . . . . . . . . . . 36-3 3605 Marine Motor Fuel-Dispensing Facilities . . . . . . . . . 36-4
CHAPTER 37 COMBUSTIBLE FIBERS . . . . . . . . . . . . . . . . .37-3
3701 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-3
3702 Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-3
3703 General Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-3
3704 Loose Fiber Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-3 3705 Baled Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-4
CHAPTER 38 RESERVED . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-1
CHAPTER 39 PROCESSING AND EXTRACTION
FACILITIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39-3
3901 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-3
3902 Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-3
3903 Processing and Extraction. . . . . . . . . . . . . . . . . . . . . . 39-3 3904 Systems and Equipment . . . . . . . . . . . . . . . . . . . . . . . 39-4 3905 Safety Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-4
CHAPTER 40 STORAGE OF DISTILLED SPIRITS
Frequently asked questions
When do I follow the CRC vs. the CMC for combustion air and vents?
For general appliance combustion‑air and venting use CMC Chapter 7 and 8 — CRC Chapters 17 and 18 are not adopted in California. Use the CRC § R1006 only for the residential fireplace exterior‑air rules.
Can I install a manually operated damper on a combustion‑air opening?
No. Manually operated dampers are prohibited in combustion‑air openings; motorized louvers may be permitted only if interlocked per § 701.12.
How high must my chimney extend above the roof?
A residential chimney must extend at least 3 ft above the highest point where it passes through the roof and at least 2 ft above any portion of the building within 10 ft horizontal — see § 802.5.4.
What mesh size is required for combustion‑air screens?
Screens shall be no smaller than 1/4‑inch (6.4 mm) mesh per § 701.10.1.
Where do I find the vent sizing tables and engineering rules?
Consult CMC Chapter 8 (tables in § 803.0 and related sections) for vent and chimney sizing; the chapter includes tables and specific rules (and reductions) and indicates when engineering methods are required.
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