What is a 'Duct' and 'Air distribution system'?

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

• 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.

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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.

• CMC § 1.0 High relevance — show source text

  D. The outdoor design temperatures for cooling shall be no greater than the 1.0 percent Cooling Dry Bulb and Mean Coincident Wet Bulb values.

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  MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS

  3. Outdoor condensing units . A. Clearances. Installed air conditioner and heat pump outdoor condensing units shall have a clearance of at least 5 feet (1.5 meters) from the outlet of any dryer vent. B. Liquid line drier. Installed air conditioner and heat pump systems shall be equipped with liquid line filter driers if required, as specified by manufacturer’s instructions.
  4. Central forced-air heating furnaces . A. Temperature rise . Central forced-air heating furnace installations shall be configured to operate in conformance with the furnace manufacturer's maximum inlet-to-outlet temperature rise specifications.
  5. Air-distribution and ventilation system ducts, plenums and fans. A. CMC compliance.

  i. All air-distribution system ducts and plenums, including, but not limited to, mechanical closets and air-handler boxes, shall meet the requirements of the CMC Sections 601.0, 602.0, 603.0, 604.0 and 605.0 and ANSI/SMACNA006-2006 HVAC Duct Construction Standards Metal and Flexible 3rd Edition, incorporated herein by reference. ii. Portions of supply-air and return-air ducts and plenums of a space heating or cooling system shall be insulated in accordance with either Subsection a or b below:

  a. Ducts shall have a minimum installed level of R-6.0, or

  Exception to Section 160.3(b)5Aiia : Portions of the duct system located in conditioned space below the ceiling separating the occupiable space from the attic are not required to be insulated if all of the following conditions are met: i. The noninsulated portion of the duct system is located entirely inside the building’s thermal envelope as confirmed by visual inspection. ii. At all locations where noninsulated portions of the duct system penetrate into unconditioned space, the penetration shall be draft stopped compliant with CFC Sections 703.1 and 704.1 and air-sealed to the construction materials that are penetrated, using materials compliant with CMC Section E502.4.2 to prevent air infiltration into the cavity. All connections in unconditioned space are insulated to a minimum of R-6.0 as confirmed by visual inspection. b. Ducts do not require insulation when the duct system is located entirely in conditioned space. For buildings with three or fewer habitable stories, duct systems located entirely in conditioned space shall be confirmed through field verification and diagnostic testing in accordance with the requirements of Reference Residential Appendix RA3.1.4.3.8. iii. Connections of metal ducts and the inner core of flexible ducts shall be mechanically fastened. iv. Openings shall be sealed with mastic, tape or other duct-closure system that meets the applicable requirements of UL 181, UL 181A or UL 181B or aerosol sealant that meets the requirements of UL 723. If mastic or tape is used to seal openings greater than [1] / 4 inch, the combination of mastic and either mesh or tape shall be used. v. Building cavities, support platforms for air handlers, and plenums designed or constructed with materials other than sealed sheet metal, duct board or flexible duct shall not be used for conveying conditioned air.

• CMC § 160.3 High relevance — show source text

  Exception 2 to Section 160.3(c)1: Piping that conveys fluids with a design operating temperature range between 60°F and 105°F.

  Exception 3 to Section 160.3(c)1: Where the heat gain or heat loss to or from piping without insulation will not increase building source energy use. Exception 4 to Section 160.3(c)1: Piping that penetrates framing members shall not be required to have pipe insulation for the distance of the framing penetration. Metal piping that penetrates metal framing shall use grommets, plugs, wrapping or other insulating material to ensure that no contact is made with the metal framing. 2. Requirements for air distribution system, ducts and plenum. Multifamily common areas shall comply with the applicable requirements of Sections 160.3(c)2A through 160.3(c)2F. A. CMC compliance. All air distribution system ducts and plenums, including, but not limited to, building cavities, mechanical closets, air-handler boxes and support platforms used as ducts or plenums shall meet the requirements of CMC Sections 601.0, 602.0, 603.0, 604.0 and 605.0, and ANSI/SMACNA-006-2006 HVAC Duct Construction Standards Metal and Flexible 3rd Edition, incorporated herein by reference. Connections of metal ducts and the inner core of flexible ducts shall be mechanically fastened. Openings shall be sealed with mastic, tape, aerosol sealant or other duct-closure system that meets the applicable requirements of UL 181, UL 181A or UL 181B. If mastic or tape is used to seal openings greater than [1] / 4 inch, the combination of mastic and either mesh or tape shall be used. B. Portions of supply-air and return-air ducts conveying heated or cooled air located in one or more of the following spaces shall be insulated to a minimum installed level of R-8:

  i. Outdoors; or ii. In a space between the roof and an insulated ceiling; or iii. In a space directly under a roof with fixed vents or openings to the outside or unconditioned spaces; or iv. In an unconditioned crawl space; or v. In other unconditioned spaces. Portions of supply-air ducts that are not in one of these spaces, including ducts buried in concrete slab, shall be insulated to a minimum installed level of R-4.2 or be enclosed in directly conditioned space. C. Duct and plenum materials. i. Factory-fabricated duct systems. a. All factory-fabricated duct systems shall comply with UL 181 for ducts and closure systems, including collars, connections and splices, and be labeled as complying with UL 181. UL 181 testing may be performed by UL laboratories or a laboratory approved by the Executive Director. b. All pressure-sensitive tapes, heat-activated tapes and mastics used in the manufacture of rigid fiberglass ducts shall comply with UL 181 and UL 181A. c. All pressure-sensitive tapes and mastics used with flexible ducts shall comply with UL 181 and UL 181B. d. Ductwork and plenums with pressure class ratings shall be constructed to Seal Class A. Joints and seams of duct systems and their components shall not be sealed with cloth back rubber adhesive duct tapes unless such tape is used in combination with mastic and drawbands.

• CMC § 140.8 High relevance — show source text

  C. An energy management control system (EMCS) or other controls that provides the specified lighting control functionality and complies with all requirements applicable to the specified controls may be used to meet these requirements. 4. Internally illuminated address signs. Internally illuminated address signs shall either: A. Comply with Section 140.8; or B. Consume no more than 5 watts of power. 5. Residential garages for eight or more vehicles. Lighting for residential parking garages for eight or more vehicles shall comply with the applicable requirements for nonresidential garages in Sections 110.9, 130.0, 130.1, 130.4, 140.6 and 141.0.

  (l) Reserved.

  (m) Air-distribution and ventilation system ducts, plenums and fans.

  1. CMC compliance.

  A. All air-distribution system ducts and plenums, including but not limited to, mechanical closets and air-handler boxes, shall meet the requirements of the CMC Sections 601.0, 602.0, 603.0, 604.0, 605.0 and ANSI/SMACNA-006-2006 HVAC Duct Construction Standards Metal and Flexible, 3rd Edition, incorporated herein by reference.

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  SINGLE-FAMILY RESIDENTIAL BUILDINGS— MANDATORY FEATURES AND DEVICES

  B. Portions of supply-air and return-air ducts and plenums of a space heating or cooling system shall be insulated in accordance with either Subsection i or ii below:

  i. Ducts shall have a minimum installed level of R-6.0, or Exception 1 to Section 150.0(m)1Bi: Portions of the duct system located in conditioned space below the ceiling separating the occupiable space from the attic are not required to be insulated if all of the following conditions are met:

  a. The noninsulated portion of the duct system is located entirely inside the building’s thermal envelope as confirmed by visual inspection. b. At all locations where noninsulated portions of the duct system penetrate into unconditioned space, the penetration shall be draft stopped compliant with CFC Sections 703.1 and 704.1 and air-sealed to the construction materials that are penetrated, using materials compliant with CMC Section E502.4.2 to prevent air infiltration into the cavity. All connections in unconditioned space are insulated to a minimum of R-6.0 as confirmed by visual inspection. Exception 2 to Section 150.0(m)1Bi : Ducts located in an unvented attic shall have a minimum insulation value of R-4.2, verified by visual inspection where:

  a. The attic has at least R-30 insulation between the roof rafters in contact with the roof deck.

  b. The gable ends meet the wall insulation requirements of Section 150.1(c)1B. c. The dwelling unit achieves a whole building leakage rate of 3.0 ACH50 or less, as confirmed by field verification and diagnostic testing in accordance with Reference Residential Appendix RA3.8. ii. Ducts do not require insulation when the duct system is located entirely within conditioned space, as confirmed through field verification and diagnostic testing in accordance with the requirements of Reference Residential Appendix RA3.1.4.3.8. For dwelling units with attics, the duct system shall be located below the ceiling separating the occupiable space from the attic.

• CMC § 160.3 High relevance — show source text

  iii. Pipe insulation buried below grade must be installed in a waterproof and noncrushable casing or sleeve.

  D. Insulation thickness.

  i. For insulation with a conductivity in the range shown in Table 160.3-D for the applicable fluid temperature range, the insulation shall have the applicable minimum thickness or R- value shown in Table 160.3-D. ii. For insulation with a conductivity outside the range shown in Table 160.3-D for the applicable fluid temperature range, the insulation shall have a minimum R- value shown in Table 160.3-D or thickness as calculated with Equation 160.3-A:

  (Equation 160.3-A)

  T = PR  1 + ------ PRt 

  K

  [-] k [-] = PR  1 + ------ t  – 1

  where:

  T = Minimum insulation thickness for material with conductivity K, inches. PR = Pipe actual outside radius, inches.

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  MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS

  t = Insulation thickness from 160.3-D, inches.

  K = Conductivity of alternate material at the mean rating temperature indicated in Table 160.3-D for the applicable fluid temperature range, in Btu-inch per hour per square foot per °F. k = The lower value of the conductivity range listed in Table 160.3-D for the applicable fluid temperature range, Btu-inch per hour per square foot per °F. Exception 1 to Section 160.3(c)1: Factory-installed piping within space-conditioning equipment certified under Section 110.1 or 110.2.

  Exception 2 to Section 160.3(c)1: Piping that conveys fluids with a design operating temperature range between 60°F and 105°F.

  Exception 3 to Section 160.3(c)1: Where the heat gain or heat loss to or from piping without insulation will not increase building source energy use. Exception 4 to Section 160.3(c)1: Piping that penetrates framing members shall not be required to have pipe insulation for the distance of the framing penetration. Metal piping that penetrates metal framing shall use grommets, plugs, wrapping or other insulating material to ensure that no contact is made with the metal framing. 2. Requirements for air distribution system, ducts and plenum. Multifamily common areas shall comply with the applicable requirements of Sections 160.3(c)2A through 160.3(c)2F. A. CMC compliance. All air distribution system ducts and plenums, including, but not limited to, building cavities, mechanical closets, air-handler boxes and support platforms used as ducts or plenums shall meet the requirements of CMC Sections 601.0, 602.0, 603.0, 604.0 and 605.0, and ANSI/SMACNA-006-2006 HVAC Duct Construction Standards Metal and Flexible 3rd Edition, incorporated herein by reference. Connections of metal ducts and the inner core of flexible ducts shall be mechanically fastened. Openings shall be sealed with mastic, tape, aerosol sealant or other duct-closure system that meets the applicable requirements of UL 181, UL 181A or UL 181B.

• CMC § 3.3.18 High relevance — show source text

  Discharge. The final portion of a duct or pipe where the product being conveyed is emptied or released from confinement; the termination point of the pipe or duct. [NFPA 96:3.3.18]

  Discrete Products in Plenums. Individual, distinct products which are non-continuous such as pipe hangers, duct registers, duct fittings, and duct straps.

  District Heating Plant. A power boiler plant designed to distribute hot water or steam to users located off the premises.

  Draft Hood. A nonadjustable device built into an appliance, or made a part of the vent connector from an appliance, that is designed to:

  (1) Provide for the ready escape of the flue gases from the appliance in the event of no draft, backdraft, or stoppage beyond the draft hood.

  (2) Prevent a backdraft from entering the appliance.

  (3) Neutralize the effect of stack action of the chimney or gas vent upon the operation of the appliance. [NFPA 54:3.3.30]

  Driver Building. One or more building(s) or facility(ies) that determined the upper and lower temperature limits of hot fluid or cold fluid delivery system.

  Dual Purpose Water Heater. An appliance intended to be a heat source for both space heating and domestic hot water applications.

  Duct. A tube or conduit for transmission of air, fumes, vapors, or dust. This definition shall not include:

  (1) A vent, vent connector, or chimney connector.

  (2) A tube or conduit wherein the pressure of the air exceeds 1 psi (7 kPa).

  (3) The air passages of listed self-contained systems.

  Duct, Environmental Air. Ducting used for conveying air at temperatures not exceeding 250°F (121°C) to or from occupied areas of any occupancy through other than heating or air-conditioning systems, such as ventilation for human usage, domestic kitchen range exhaust, bathroom exhaust ducts, locker room exhaust ducts, shower room exhaust ducts, janitor’s closet exhaust ducts, and domestic-type clothes dryer exhaust ducts.

  Duct, Grease. A containment system for the transportation of air and grease vapors that is designed and

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  36 2025 CALIFORNIA MECHANICAL CODE

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  DEFINITIONS

  Electrical Code. The National Electrical Code promulgated by the National Fire Protection Association, as adopted by this jurisdiction. [HCD 1 & HCD 2] Whenever the term “Electrical Code” is used in this code, it shall mean the Cal- ifornia Electrical Code, Title 24, Part 3.

  Emergency Alarm System. A system intended to provide notification and warning of abnormal conditions and summon appropriate aid.

  Emergency Control Station. An approved location on the premises where signals from emergency equipment are received.

  Enforcing Agency. [HCD 1, HCD 2, SFM, OSHPD 1, 1R, 2, 3, 4, 5 & 6] “Enforcing Agency” is the designated department or agency as specified by statute and regulation.

• California Mechanical Code High relevance — show source text

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  ALL OCCUPANCIES—GENERAL PROVISIONS

  DEW POINT TEMPERATURE is the vapor saturation temperature at a specified pressure for a substance undergoing phase change from vapor to liquid.

  DIRECT DIGITAL CONTROL (DDC) is a type of control where controlled and monitored analog or binary data, such as temperature and contact closures, are converted to digital format for manipulation and calculations by a digital computer or microprocessor, then converted back to analog or binary form to control mechanical devices.

  DIRECT-VENT APPLIANCE or “sealed combustion” appliance is an appliance that is constructed and installed so that air from combustion is derived directly from the outdoors and flue gases are discharged to the outdoors.

  DISPLAY PERIMETER is the length of an exterior wall in a Group B; Group F, Division 1; or Group M Occupancy that immediately abuts a public sidewalk, measured at the sidewalk level for each story that abuts a public sidewalk.

  DOMESTIC HOT WATER SYSTEM APPURTENANCE are all elements that are in series in a domestic hot water distribution system, including fittings (elbows, tees, flanges, etc.), pumps, valves (isolation, mixing, balancing, check, etc.), strainers, hose bibs, coil ubends, meters, sensors, heat exchangers and air separators.

  DOMESTIC WATER HEATING SYSTEMS ( see “service water heating”).

  DOOR is an operable opening in the building envelope including swinging and roll-up doors, fire doors, pet doors and access hatches with less than 25 percent glazed area. When that operable opening has 25 percent or more glazed area it is a glazed door. See Fenestration: Glazed Door.

  DOOR AREA is the total rough opening area which includes the door, and when present, the fenestration, and the fenestration frame components in the door frame assembly.

  DRAIN WATER HEAT RECOVERY (DWHR) is a system that recovers heat from effluent in waste piping and uses it to preheat water in a domestic or service water-heating system in order to reduce water-heating energy usage.

  DRY COOLER is a fan-powered heat rejection device that includes a water or glycol circuit connected by a closed circulation loop refrigerant condenser and is air-cooled.

  DUAL-FUEL HEAT PUMP is an electric heat pump with gas furnace supplemental heat that alternates between the two fuel sources.

  DUCT SEALING is a procedure for installing a space-conditioning distribution system that minimizes leakage of air from or to the distribution system. Minimum specifications for installation procedures, materials, diagnostic testing and field verification are contained in the Reference Residential Appendix RA3 and Reference Nonresidential Appendix NA1.

  DUCT SYSTEM is all the ducts, duct fittings, plenums and fans when assembled to form a continuous passageway for the distribution of air.

  DUCT WALL PENETRATIONS are openings to the duct wall made by pipes, holes, conduit, tie rods or wires.

  DUCTED SYSTEM is an air conditioner or heat pump, either a split system or single-packaged unit, that is designed to be permanently installed equipment and delivers conditioned air to an indoor space through a duct.

  DWELLING is a building that contains one or two dwelling units used, intended or designed to be used, rented, leased, let or hired out to be occupied for living purposes.

• California Mechanical Code High relevance — show source text

  DOOR AREA is the total rough opening area which includes the door, and when present, the fenestration, and the fenestration frame components in the door frame assembly.

  DRAIN WATER HEAT RECOVERY (DWHR) is a system that recovers heat from effluent in waste piping and uses it to preheat water in a domestic or service water-heating system in order to reduce water-heating energy usage.

  DRY COOLER is a fan-powered heat rejection device that includes a water or glycol circuit connected by a closed circulation loop refrigerant condenser and is air-cooled.

  DUAL-FUEL HEAT PUMP is an electric heat pump with gas furnace supplemental heat that alternates between the two fuel sources.

  DUCT SEALING is a procedure for installing a space-conditioning distribution system that minimizes leakage of air from or to the distribution system. Minimum specifications for installation procedures, materials, diagnostic testing and field verification are contained in the Reference Residential Appendix RA3 and Reference Nonresidential Appendix NA1.

  DUCT SYSTEM is all the ducts, duct fittings, plenums and fans when assembled to form a continuous passageway for the distribution of air.

  DUCT WALL PENETRATIONS are openings to the duct wall made by pipes, holes, conduit, tie rods or wires.

  DUCTED SYSTEM is an air conditioner or heat pump, either a split system or single-packaged unit, that is designed to be permanently installed equipment and delivers conditioned air to an indoor space through a duct.

  DWELLING is a building that contains one or two dwelling units used, intended or designed to be used, rented, leased, let or hired out to be occupied for living purposes.

  DWELLING UNIT is a single unit providing complete, independent living facilities for one or more persons including access, permanent provisions for living, sleeping, eating, cooking and sanitation.

  DWELLING UNIT, ATTACHED is a dwelling unit that shares a common wall or common floor/ceiling with another dwelling unit.

  DWELLING UNIT, JUNIOR ACCESSORY, or JADU is a dwelling unit that is no more than 500 square feet in size and contained entirely within a newly constructed or existing single-family building. A JADU includes a kitchen, a separate entrance from the main entrance to the building, and an interior entry to the main living area. A JADU may include separate sanitation facilities, or may share sanitation facilities within the newly constructed or existing single-family building.

  DX-DEDICATED OUTDOOR AIR SYSTEM UNIT (DX-DOAS) is a type of air-cooled, water-cooled or water-source DOAS unit that dehumidifies 100-percent outdoor air and includes reheat that is capable of controlling the supply dry-bulb temperature of the dehumidified air to the designed supply air temperature. This conditioned outdoor air is then delivered directly or indirectly to the conditioned spaces. It may precondition outdoor air by containing an enthalpy wheel, sensible wheel, desiccant wheel, plate heat exchanger, heat pipes, or other heat or mass transfer apparatus.

  EAST-FACING (See “orientation.”)

  ECONOMIZER, AIR, is a ducting arrangement, including dampers, linkages and an automatic control system that allows a cooling supply fan system to supply outside air to reduce or eliminate the need for mechanical cooling.

  ECONOMIZER, PUMPED REFRIGERANT, is a system by which the supply air of a cooling system is cooled directly by refrigerant pumped between indoor and outdoor units during cooler ambient temperatures in order to reduce or eliminate the need for mechanical cooling.

• CMC § 3.3.22.2.1 Medium relevance — show source text

  processes.

  Factory-Built Grease Duct Enclosures. A listed factory-built grease duct system evaluated as an enclosure system for reduced clearances to combustibles and as an alternative to a duct with its fire-rated enclosure. [NFPA 96:3.3.22.2.1]

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  installed to reduce the possibility of the accumulation of combustible condensation and the occurrence of damage if a fire occurs within the system. [NFPA 96:3.3.20.2] Duct, Product-Conveying. Ducting used for conveying solid particulates, such as refuse, dust, fumes, and smoke; liquid particulate matter, such as spray residue, mists, and fogs; vapors, such as vapors from flammable or corrosive liquids; noxious and toxic gases; and air at temperatures exceeding 250°F (121°C).

  Duct Furnace. A furnace normally installed in distribution ducts of air-conditioning systems to supply warm air for heating. This definition applies only to an appliance that, for air circulation, depends on a blower not furnished as part of the furnace. [NFPA 54:3.3.45.3] Duct Sealing. The use of approved adhesives, gaskets, tape, mastics, or combination thereof to close openings in the surface of the ductwork, field erected plenums, equipment, and casings through which air leakage would occur, or the use of continuous welds.

  Duct Sealing Classes. Seal Class A. All transverse joints, longitudinal seams, and duct wall penetrations. Seal Class B. All transverse joints and longitudinal

  seams.

  Seal Class C. Transverse joints. Duct System. A continuous passageway for the transmission of air and vapors that, in addition to the containment components themselves, might include duct fittings, dampers, plenums, other items, and air-handling equipment. [NFPA 96:3.3.20]

  Ductless Mini-Split System. A heating and cooling equipment that includes one or multiple indoor evaporator, air handler, or both units, an outdoor condensing unit that is connected by refrigerant piping, and electrical wiring. A ductless mini-split system is capable of cooling or heating one or more rooms without the use of traditional ductwork.

  Dwelling. A building or portion thereof that contains not more than two dwelling units.

  Dwelling Unit. A building or portion thereof that contains living facilities, including provisions for sleeping, eating, cooking, and sanitation, as required by this code, for not more than one family.

  207.0 – E –

  Easily Accessible. See Accessible, Readily . Effective Ground-Fault Current Path. An intentionally constructed, low impedance electrically conductive path designed and intended to carry current under ground-fault conditions from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground-fault detectors. [NFPA 54:3.3.33]

  Electric Duct Heaters. A heater located in the airstream of a forced-air system where the air-moving unit is not provided as an integral part of the equipment.

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• CMC § 8.5 Medium relevance — show source text

  21_–0.27|75|0.75 inch|0.75 inch|1.0 inch|1.0 inch|1.0 inch| |Residential
  40–60|0.21–0.27|75|R-6|R-5|R-7|R-6|R-5| |Nonresidential
  40–60|0.21–0.27|75|0.5 inch|0.5 inch|1.0 inch|1.0 inch|1.0 inch| |Nonresidential
  40–60|0.21–0.27|75|R-3|R-3|R-7|R-6|R-5| |Below 40|0.20–0.26|50|1.0 inch|1.5 inches|1.5 inches|1.5 inches|1.5 inches| |Below 40|0.20–0.26|50|R 8.5|R 14|R 12|R 10|R 9|

  Footnote to Table 120.3-A-1 and Table 120.3-A-2: These thicknesses are based on energy efficiency considerations only. Issues such as water vapor permeability or surface condensation sometimes require vapor retarders or additional insulation.

  SECTION 120.4—REQUIREMENTS FOR AIR DISTRIBUTION SYSTEM DUCTS AND PLENUMS

  Nonresidential and hotel/motel buildings shall comply with the applicable requirements of Sections 120.4(a) through 120.4(g).

  Exception to Section 120.4: Systems serving healthcare facilities shall comply with the applicable requirements of the California Mechanical Code.

  (a) CMC compliance. All air distribution system ducts and plenums, including but not limited to building cavities, mechanical closets, air-handler boxes and support platforms used as ducts or plenums, shall meet the requirements of the CMC Sections 601.0, 602.0, 603.0, 604.0, and 605.0, and ANSI/SMACNA-006-2006 HVAC Duct Construction Standards Metal and Flexible, 3rd Edition incorporated herein by reference. Connections of metal ducts and the inner core of flexible ducts shall be mechanically fastened. Openings shall be sealed with mastic, tape, aerosol sealant or other duct-closure system that meets the applicable requirements of UL 181, UL 181A, or UL 181B. If mastic or tape is used to seal openings greater than [1] / 4 inch, the combination of mastic and either mesh or tape shall be used.

  Portions of supply-air and return-air ducts conveying heated or cooled air located in one or more of the following spaces shall be insulated to a minimum installed level of R-8:

  1. Outdoors; or

  2. In a space between the roof and an insulated ceiling; or

  3. In a space directly under a roof with fixed vents or openings to the outside or unconditioned spaces; or

  4. In an unconditioned crawlspace; or

  5. In other unconditioned spaces.

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• CMC § 120.4 Medium relevance — show source text

  Nonresidential and hotel/motel buildings shall comply with the applicable requirements of Sections 120.4(a) through 120.4(g).

  Exception to Section 120.4: Systems serving healthcare facilities shall comply with the applicable requirements of the California Mechanical Code.

  (a) CMC compliance. All air distribution system ducts and plenums, including but not limited to building cavities, mechanical closets, air-handler boxes and support platforms used as ducts or plenums, shall meet the requirements of the CMC Sections 601.0, 602.0, 603.0, 604.0, and 605.0, and ANSI/SMACNA-006-2006 HVAC Duct Construction Standards Metal and Flexible, 3rd Edition incorporated herein by reference. Connections of metal ducts and the inner core of flexible ducts shall be mechanically fastened. Openings shall be sealed with mastic, tape, aerosol sealant or other duct-closure system that meets the applicable requirements of UL 181, UL 181A, or UL 181B. If mastic or tape is used to seal openings greater than [1] / 4 inch, the combination of mastic and either mesh or tape shall be used.

  Portions of supply-air and return-air ducts conveying heated or cooled air located in one or more of the following spaces shall be insulated to a minimum installed level of R-8:

  1. Outdoors; or

  2. In a space between the roof and an insulated ceiling; or

  3. In a space directly under a roof with fixed vents or openings to the outside or unconditioned spaces; or

  4. In an unconditioned crawlspace; or

  5. In other unconditioned spaces.

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  NONRESIDENTIAL, HOTEL/MOTEL OCCUPANCIES, AND COVERED PROCESSES—MANDATORY REQUIREMENTS

  Portions of supply-air ducts that are not in one of these spaces, including ducts buried in concrete slab, shall be insulated to a minimum installed level of R-4.2 or be enclosed in directly conditioned space.

  (b) Duct and plenum materials.

  1. Factory-fabricated duct systems. A. All factory-fabricated duct systems shall comply with UL 181 for ducts and closure systems, including collars, connections and splices, and be labeled as complying with UL 181. UL 181 testing may be performed by UL laboratories or a laboratory approved by the Executive Director. B. All pressure-sensitive tapes, heat-activated tapes, and mastics used in the manufacture of rigid fiberglass ducts shall comply with UL 181 and UL 181A. C. All pressure-sensitive tapes and mastics used with flexible ducts shall comply with UL 181 and UL 181B. D. All ductwork and plenums with pressure class ratings shall be constructed to Seal Class A. Joints and seams of duct systems and their components shall not be sealed with cloth-back rubber adhesive duct tapes unless such tape is used in combination with mastic and drawbands.

  Exception to Section 120.4(b)1D: Ductwork located in occupied space and exposed to view is not required to meet Seal Class A.

• CMC § 503.0. Medium relevance — show source text

  The heating, ventilation, and air-conditioning system of other buildings shall be in accordance with Section E 503.0. E 502.2 Heating, Ventilating, and Air-Conditioning Systems and Equipment. This section shall regulate only equipment using single-phase electric power, air conditioners, and heat pumps with rated cooling capacities less than 65 000 British thermal units per hour (Btu/h) (19 kW), warm air furnaces with rated heating capacities less than 225 000 Btu/h (66 kW), boilers less than 300 000 Btu/h (88 kW) input, and heating-only heat pumps with rated heating capacities less than 65 000 Btu/h (19 kW). [ASHRAE 90.2:6.2] E 502.2.1 Nonresidential Type Systems and Equipment. Heating, ventilating, and air-conditioning systems and equipment that do not fall under the requirements of Section E 502.0 shall be in accordance with the applicable requirements of Section E 503.0. E 502.3 Balancing. The air distribution system design, including outlet grilles, shall provide a means for balancing the air distribution system unless the design procedure provides a system intended to operate within plus or minus 10 percent of design air quantities. [ASHRAE 90.2:6.3] E 502.3.1 Balancing Dampers. Balancing dampers shall be installed in branch ducts, and the axis of the damper shall be installed parallel to the direction of airflow in the main duct.

  E 502.4 Ducts. Ducts shall be sized, installed, and tested in accordance with Section E 502.4.1 through Section E 502.4.4.

  E 502.4.1 Insulation for Ducts. Portions of the air distribution system installed in or on buildings for heating and cooling shall be R-8. Where the mean outdoor dewpoint temperature in a month exceeds 60°F (16°C), vapor retarders shall be installed on conditioned-air supply ducts. Vapor retarders shall have a water vapor permeance not exceeding 0.5 perm [2.87 E-11 kg/(Pa•s•m [2] )] where tested in accordance with Procedure A in ASTM E96.

  Insulation shall not be required where the ducts are within the conditioned space. [ASHRAE 90.2:6.4] E 502.4.2 Ducts and Register Penetrations. Joints, seams, and penetrations of duct systems shall be made airtight by means of mastics, gasketing, or other means in accordance with this code. Register penetrations shall be sealed to the wall or floor assemblies. Where HVAC duct penetrates a conditioned space, the duct penetration shall be sealed to the wall or floor assembly to prevent leakage into an unconditioned space.

  2025 CALIFORNIA MECHANICAL CODE 415

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  APPENDIX E

  E 502.4.3 Duct Leakage Test. For systems with a duct or air handler outside of the conditioned space, a duct leakage test shall be performed in accordance with Section E 502.4.3.1.

• CMC § 160.3 High relevance — show source text

  Mass radiant floor slab systems shall incorporate floor temperature onto the optimum start algorithm. Exception to Section 160.3(a)2J: Systems that must operate continuously.

  (b) Dwelling unit space-conditioning and air distribution systems.

  1. Building cooling and heating loads. Building heating and cooling loads shall be determined using a method based on any one of the following, using cooling and heating loads as two of the criteria for equipment sizing and selection: A. The ASHRAE Handbook, Equipment Volume, Applications Volume and Fundamentals Volume; or B. The SMACNA Residential Comfort System Installation Standards Manual; or

  C. The ACCA Manual J.

  Exception to Section 160.3(b)1: Block loads, the total load for all rooms combined that are served by the central equipment, may be used for the purpose of system sizing for additions. NOTE: Heating systems are required to have a minimum heating capacity adequate to meet the minimum requirements of the CBC.

  2. Design conditions . Design conditions shall be determined in accordance with the following: A. For the purpose of sizing the space-conditioning (HVAC) system, the indoor design temperatures shall be 68°F for heating and 75°F for cooling. B. Outdoor design conditions shall be selected from one of the following: i. Reference Joint Appendix JA2, which is based on data from the ASHRAE Climatic Data for Region X; or ii. The ASHRAE Handbook Fundamentals Volume; or

  iii. The ACCA Manual J.

  C. The outdoor design temperatures for heating shall be no lower than the 99.0 percent Heating Dry Bulb or the Heating Winter Median of Extremes values.

  D. The outdoor design temperatures for cooling shall be no greater than the 1.0 percent Cooling Dry Bulb and Mean Coincident Wet Bulb values.

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  MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS

  3. Outdoor condensing units . A. Clearances. Installed air conditioner and heat pump outdoor condensing units shall have a clearance of at least 5 feet (1.5 meters) from the outlet of any dryer vent. B. Liquid line drier. Installed air conditioner and heat pump systems shall be equipped with liquid line filter driers if required, as specified by manufacturer’s instructions.
  4. Central forced-air heating furnaces . A. Temperature rise . Central forced-air heating furnace installations shall be configured to operate in conformance with the furnace manufacturer's maximum inlet-to-outlet temperature rise specifications.
  5. Air-distribution and ventilation system ducts, plenums and fans. A. CMC compliance.

  i. All air-distribution system ducts and plenums, including, but not limited to, mechanical closets and air-handler boxes, shall meet the requirements of the CMC Sections 601.0, 602.0, 603.0, 604.0 and 605.0 and ANSI/SMACNA006-2006 HVAC Duct Construction Standards Metal and Flexible 3rd Edition, incorporated herein by reference. ii. Portions of supply-air and return-air ducts and plenums of a space heating or cooling system shall be insulated in accordance with either Subsection a or b below:

  a. Ducts shall have a minimum installed level of R-6.0, or

• CMC § 150.0 High relevance — show source text

  Forward phase cut dimmers controlling LED light sources in these spaces shall comply with NEMA SSL 7A. Exception 1 to Section 150.0(k)2F: Ceiling fans may provide control of integrated lighting via a remote control. Lighting integral to kitchen range hoods and bathroom exhaust fans. Exception 2 to Section 150.0(k)2F: Luminaires connected to a circuit with controlled lighting power less than 20 watts or controlled by an occupancy or vacancy sensor providing automatic-off functionality. Exception 3 to Section 150.0(k)2F: Navigation lighting rated less than 5 watts, such as night lights, step lights, and path lights. Lighting controlled by automatic-off controls and located internal to drawers, cabinetry with opaque fronts, or cabinetry with doors. G. Independent controls. Lighting integrated with the exhaust fans shall be controlled independently from the fans. The following shall be controlled separately from ceiling-installed lighting such that one can be turned on without turning on the other: i. Undercabinet lighting. ii. Undershelf lighting. iii. Interior lighting of display cabinets.

  iv. Switched outlets.

  3. Residential outdoor lighting. In addition to meeting the requirements of Section 150.0(k)1A, luminaires providing residential outdoor lighting shall meet the following requirements, as applicable: A. Outdoor lighting permanently mounted to a residential building or to other buildings on the same lot shall meet the following requirements: i. Controlled by a manual ON and OFF control switch that permits the automatic actions of Item ii below; and ii. Controlled by one of the following controls: a. A photocell and a motion sensor; or b. A photocell and an automatic time switch control; or c. Controlled by an astronomical time clock control. B. Controls that override to ON shall not be allowed unless the override automatically returns the automatic control to its normal operation within 6 hours. C. An energy management control system (EMCS) or other controls that provides the specified lighting control functionality and complies with all requirements applicable to the specified controls may be used to meet these requirements.
  4. Internally illuminated address signs. Internally illuminated address signs shall either: A. Comply with Section 140.8; or B. Consume no more than 5 watts of power.
  5. Residential garages for eight or more vehicles. Lighting for residential parking garages for eight or more vehicles shall comply with the applicable requirements for nonresidential garages in Sections 110.9, 130.0, 130.1, 130.4, 140.6 and 141.0.

  (l) Reserved.

  (m) Air-distribution and ventilation system ducts, plenums and fans.

  1. CMC compliance.

  A. All air-distribution system ducts and plenums, including but not limited to, mechanical closets and air-handler boxes, shall meet the requirements of the CMC Sections 601.0, 602.0, 603.0, 604.0, 605.0 and ANSI/SMACNA-006-2006 HVAC Duct Construction Standards Metal and Flexible, 3rd Edition, incorporated herein by reference.

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  SINGLE-FAMILY RESIDENTIAL BUILDINGS— MANDATORY FEATURES AND DEVICES

  B. Portions of supply-air and return-air ducts and plenums of a space heating or cooling system shall be insulated in accordance with either Subsection i or ii below:

• CMC § 1.4.3.2 High relevance — show source text

  B. For single-family dwellings and townhouses at the rough-in stage of construction prior to installation of the dwelling’s interior finishing: i. Air-handling unit installed. If the air-handling unit is installed and the ducts are connected directly to the air handler, the total leakage of the duct system shall not exceed 5 percent of the air handler airflow as determined utilizing the procedures in Reference Residential Appendix Sections RA3.1.4.3.2, RA3.1.4.3.2.1 and RA3.1.4.3.3. ii. Air-handling unit not yet installed. If the air-handling unit is not yet installed, the total leakage of the duct system shall not exceed 4 percent of the air handler airflow as determined utilizing the procedures in Reference Residential Appendix Sections RA3.1.4.3.2, RA3.1.4.3.2.2 and RA3.1.4.3.3.

  12. Air filtration.

  A. System types specified in Subsections i, ii, and iii shall be provided with air filters in accordance with Sections 150.0(m)12B, 150.0(m)12C, and 150.0(m)12D. System types specified in Subsection i shall also comply with Section 150.0(m)12E.

  i. Mechanical space-conditioning systems that supply air to an occupiable space through ductwork exceeding 10 feet (3 m) in length. ii. Mechanical supply-only ventilation systems and makeup air systems that provide outside air to an occupiable

  space.

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  SINGLE-FAMILY RESIDENTIAL BUILDINGS— MANDATORY FEATURES AND DEVICES

  iii. The supply side of mechanical balanced ventilation systems, including heat recovery ventilation systems, and energy recovery ventilation systems that provide outside air to an occupiable space. Exception 1 to Section 150.0(m)12A: Evaporative coolers are not required to comply with the air filtration requirements in Section 150.0(m)12.

  B. System design and installation. i. The system shall be designed to ensure that all recirculated air and all outdoor air supplied to the occupiable space is filtered before passing through any system’s thermal conditioning components. Exception 1 to Section 150.0(m)12Bi: For heat recovery ventilators and energy recovery ventilators the location of the filters required by Section 150.0(m)12 may be downstream of a system thermal conditioning component, provided the system is equipped with ancillary filtration upstream of the system’s thermal conditioning component. ii. All systems shall be designed to accommodate the clean-filter pressure drop imposed by the system air filter(s). The design airflow rate and maximum allowable clean-filter pressure drop at the design airflow rate applicable to each air filter shall be determined and reported on labels according to Subsection iv below. Systems specified in Section 150.0(m)12Ai shall be equipped with air filters that meet either Subsection a or b below. a. Nominal two-inch minimum depth filter(s) shall be sized by the system designer, or b. Nominal one-inch minimum depth filter(s) shall be allowed if the filter(s) are sized according to Equation 150.0-A, based on a maximum face velocity of 150 ft per minute, and according to the maximum allowable clean-filter pressure drop specified in Section 150.0(m)12Dii.

• CMC § 0.0929 High relevance — show source text

  (1) 60 CFM/person for cultivation, production, and processing facilities or factories.

  (2) 15 CFM/person for centers and dispensaries.

  Ra = outdoor airflow rate required per unit area, 1 CFM/ft [2]

  For SI Units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute =

  0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per

  minute per square foot = 5.08 [(L/s)/m [2] ]

  Sample Calculation: Determine the outdoor airflow required in the breathing zone ( Vbz ) of an indoor space used for horticultural cultivation with an occupiable floor area of 800 square feet and a maximum of 5 people expected to occupy the zone.

  Sample Solution: Vbz = Rp - Pz + Ra - Az Vbz = (60 CFM/person • 5 people) + (1 CFM • 800 SF) Vbz = 1100 CFM. The ventilation system shall be capable of providing not less than 1100 CFM of outdoor air.

  I 801.1.2 Ventilation System Requirements. When activated by the gas detection system required by Section I 601.1, the mechanical purge ventilation system shall remain on until manually reset. The purge ventilation system ducting shall terminate outdoors in an approved location. The ventilation system shall be designed to operate at a negative pressure of 0.01 inches water column (0.002 kPa) in relation to the exhausted indoor space.

  I 801.1.3 Ventilation for Indoor Cultivation and Storage Spaces. Indoor spaces used for horticultural cultivation and processing and storage shall be provided with ventilation in accordance with Section 402.2. Where

  mechanical ventilation is provided, the systems shall be operational when the indoor space(s) are occupied. Air in indoor cultivation and storage spaces shall be classified as Class 2 Air in accordance with Section 403.9.2.

  I 801.1.4 Exhaust Ventilation Rate. The exhaust and ventilation system required in this section shall not create a lesser standard of installation than prescribed by the

  minimum safety standards adopted by the Authority Having Jurisdiction. Exhaust airflow shall be provided at not less than 0.2 CFM/ft [2] [1.02 (L/s)/m [2] ] of floor area. Exhaust air shall not be used as makeup air, recirculated air, or transfer air. Makeup air shall be provided for more than 150 CFM (70.8 L/s) exhaust. I 801.1.5 Exhaust System Requirements. An exhaust system shall be installed in accordance with Section 505.0 and the following requirements:

  (1) Exhaust outlet location(s) in accordance with Section 502.2.3 for product conveying ducts as classified in Section 505.8.

  (2) Exhaust air shall terminate directly to the outdoors and shall not be directed onto a public way.

  (3) The exhaust inlet shall be not less than 12 inches (305 mm) above the finished floor.

  (4) Chemical fume hoods shall be required for flammable solvent processing, shall be listed, and shall be installed in accordance with the manufacturer’s

  installation instructions.

  (5) Exhaust ducts shall be independent of all other exhaust systems.

  (6) The exhaust rate shall be in accordance with the appliable occupancy category as shown in Table 403.7.

• CMC § 510.1.2 Medium relevance — show source text

  510.1.2 Interconnection. Duct systems shall not be interconnected with any other building ventilation or exhaust system. [NFPA 96:7.1.3]

  510.1.3 Duct Installation. All ducts shall be installed with a minimum slope of ¼ inch per linear foot (20.8 mm/m) on horizontal runs up to 75 feet (22 860 mm) and a minimum slope of 1 inch per linear foot (83.2 mm/m) on horizontal runs greater than 75 feet (22 860 mm). Factory-built grease ducts shall be permitted to be installed at a lesser slope in accordance with the listing and the manufacturer’s instructions. All horizontal ducts shall be provided with access in accordance with Section 510.3.3.

  Drains shall be provided at low points in horizontal ducts. Where provided, drains shall be continuously welded to the exhaust duct or in accordance with the terms of the listing and the manufacturer’s installation manual.

  All ducts shall be installed without forming dips or traps. In manifold (common duct) systems, the lowest end of the main duct shall be connected flush on the bottom with the branch duct. [NFPA 96:7.1.5 – 7.1.5.5]

  510.1.4 Accessibility. Openings required for accessibility shall comply with Section 510.3 through Section 510.3.2. [NFPA 96:7.1.6]

  510.1.5 Sign. A sign stating the following shall be placed on all access panels:

  ACCESS PANEL – DO NOT OBSTRUCT [NFPA 96:7.1.7]

  510.1.6 Bracing and Supports. Duct bracing and supports shall be of noncombustible material, securely attached to the structure and designed to carry gravity and lateral loads within the stress limitations of the building code. Bolts, screws, rivets, and other mechanical fasteners shall not penetrate duct walls.

  510.1.7 Type I Exhaust Duct Systems. Listed grease ducts shall be installed in accordance with the terms of their listing and the manufacturer’s instructions. [NFPA 96:7.1.8]

  510.1.8 Independent Grease Duct System. Single or combined Type I exhaust systems shall be independent of other exhaust systems.

  510.2 Clearance. Clearance between ducts and combustible materials shall be provided in accordance with the requirements of Section 507.4 through Section 507.4.3.3. [NFPA 96:7.2] 510.3 Openings. Openings shall be provided at the sides or at the top of the duct, whichever is more accessible, and at changes of direction. Openings shall be protected by approved access constructed and installed in accordance with the requirements of Section 510.3.7. [NFPA 96:7.3.1, 7.3.2]

  Exception: Openings shall not be required in portions of the duct that are accessible from the duct entry or discharge.

  [NFPA 96:7.3.3]

  510.3.1 Access Panel. For hoods with dampers in the exhaust or supply collar, an access panel for cleaning and inspection shall be provided in the duct or the hood within 18 inches (457 mm) of the damper. [NFPA 96:7.3.4]

  Exception: Dampers that are accessible from under the hood.

• CMC § 203.0 Medium relevance — show source text

  Nonvoting

  Alexander Ing, National Fire Protection Association (NFPA) [R/S/T] Matthew Barker, National Fire Protection Association (NFPA) [R/S/T] Taylor Duran, IAPMO Staff Liaison David Gans, Ex-Officio IAPMO [E]

  COMMITTEE MEMBERSHIP CLASSIFICATION ABBREVIATIONS

  These classifications apply to Technical Committee members and represent their principal interest in the activity of a committee. M Manufacturer : A representative of a maker or marketer of a product, assembly or system, or portion thereof, that is affected by the standard. U User : A representative of an entity that is subject to the provisions of the standard or that voluntarily uses the standard. I/M Installer/Maintainer : A representative of an entity that is in the business of installing or maintaining a product, assembly or system affected by

  the standard.

  L Labor : A labor representative or employee concerned with safety in the workplace. R/S/T Research/Standards/Testing Laboratory : A representative of an independent research organization; an organization that develops codes, standards or other similar documents; or an independent testing laboratory. E Enforcing Authority : A representative or an agency or an organization that promulgates and/or enforces standards. C Consumer : A person who is, or represents, the ultimate purchaser of a product, system, or service affected by the standard, but who is not

  included in the User classification.

  SE Special Expert : A person not representing any of the previous classifications, but who has special expertise in the scope of the standard or portion

  thereof.

  xx 2025 CALIFORNIA MECHANICAL CODE

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

  SECTION RELOCATION

  2024 Location	2021 Location
  203.0 Closed Combustion Solid-Fuel-Burning Appliance	205.0 Closed Combustion Solid-Fuel-Burning Appliance
  203.0 Direct Vent Appliance	206.0 Direct Vent Appliances
  203.0 Electric Heating Appliance	207.0 Electric Heating Appliance
  203.0 Portable Heating Appliance	218.0 Portable Heating Appliance
  204.0 Hot-Water-Heating Boiler	210.0 Hot-Water-Heating Boiler
  204.0 Low-Pressure Hot-Water- Heating Boiler	214.0 Low-Pressure Hot-Water- Heating Boiler
  204.0 Low-Pressure Steam- Heating Boiler	214.0 Low-Pressure Steam- Heating Boiler
  204.0 Miniature Boiler	215.0 Miniature Boiler
  204.0 Package Boiler	218.0 Package Boiler
  204.0 Power Boiler	218.0 Power Boiler
  204.0 Power Hot Water Boiler (High Temperature Water Boiler)	218.0 Power Hot Water Boiler (High Temperature Water Boiler)
  204.0 Steam-Heating Boiler	221.0 Steam-Heating Boiler
  204.0 Water Heater or Hot- Water-Heating Boiler	225.0 Water Heater or Hot- Water-Heating Boiler
  206.0 Environmental Air Duct	207.0 Environmental Air Duct
  206.0 Grease Duct	209.0 Grease Ducts
  206.

• CMC § 13.5.7 Medium relevance — show source text

  [OSHPD 1 & 4]**_ Modify ASCE 7, Section 13.5.7, by the following:

  All access floors shall be special access floors in accordance with Section 13.5.7.2, except for raised roof or exterior floor paver systems.

  1617A.1.23 ASCE 7, Section 13.6.2.1. [OSHPD 1 & 4] Modify ASCE 7 Section 13.6.2.1 by adding the following to the end of the section:

  Use of this section shall be considered as an alternative system. Alternatively, HVACR systems shall require special seismic certifica- tion in accordance with Section 1705A.14.3 of this code.

  1617A.1.24 ASCE 7, Section 13.6.5. Replace ASCE 7, Section 13.6.5 as follows:

  13.6.5 Distribution Systems: Conduit, Cable Tray and Raceways. Cable trays and raceways shall be designed for seismic forces and seismic relative displacements as required in Section 13.3. Conduit equal to or greater than 2.5 inches (64 mm) trade size and attached to panels, cabinets or other equipment subject to seismic relative displacement, D pI, shall be provided with flexible connections or designed for seismic forces and seismic relative displacements as required in Section 13.3.

  Exceptions:

  1. Design for the seismic forces and relative displacements of Section 13.3 shall not be required for raceways where flexible connections or other assemblies are provided between the cable tray or raceway and associated components to accommodate the relative displacement, where the cable tray or raceway is positively attached to the structure, and one of the following apply: a. Trapeze assemblies with [3] / 8 inch (10 mm) or [1] / 2 inch (13-mm) in diameter rod hangers not exceeding 12 inches (305 mm) in length from the conduit, cable tray or raceway support point to the connection at the supporting structure are used to support the cable tray or raceway, and the total weight supported by any single trapeze is 100 pounds (445 N) or less; or b . The conduit, cable tray or raceway is supported by individual rod hangers [3] / 8 inch (10 mm) or [1] / 2 inch (13 mm) in diameter, and each hanger in the raceway run is 12 inches (305 mm) or less in length from the conduit, cable tray or raceway support point connection to the supporting structure, and the total weight supported by any single rod is 50 pounds (220 N) or less.
  2. Design for the seismic forces and relative displacements of Section 13.3 shall not be required for conduit, regardless of the value of I p, where the conduit is less than 2.5 inches (64 mm) trade size. Design for the displacements across seismic joints shall be required for conduit, cable trays and raceways with I p = 1.5 without consideration of conduit size.

  1617A.1.25 ASCE 7, Section 13.6.6. Replace ASCE 7, Section 13.6.6 with the following:

  13.6.6 Distribution Systems: Duct Systems . HVACR and other duct systems shall be designed for seismic forces and seismic relative displacements as required in Section 13.3.

• CMC § 905.8 Medium relevance — show source text

  905.8 Installation in Commercial

  Garages and Aircraft Hangars . . . 203

  905.9 Electric Duct Heaters . . . . . . . . . . 203

  906.0 Floor Furnaces . . . . . . . . . . . . . . . 203

  906.1 Application . . . . . . . . . . . . . . . . . . 203

  906.2 Installation . . . . . . . . . . . . . . . . . . 204

  906.3 Temperature Limit Controls . . . . . 204

  906.4 Combustion and Circulating Air. . . 204

  906.5 Placement. . . . . . . . . . . . . . . . . . . 204

  906.6 Bracing . . . . . . . . . . . . . . . . . . . . . 204

  906.7 Support . . . . . . . . . . . . . . . . . . . . . 204

  906.8 Clearance . . . . . . . . . . . . . . . . . . . 204

  906.9 Access . . . . . . . . . . . . . . . . . . . . . 204

  906.10 Seepage Pan . . . . . . . . . . . . . . . . 204

  906.11 Wind Protection . . . . . . . . . . . . . . 204

  906.12 Upper Floor Installations. . . . . . . . 204

  906.13 First Floor Installation . . . . . . . . . . 204

  906.14 Oil-Fired Floor Furnaces. . . . . . . . 204

  xxxv

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

  TABLE OF CONTENTS

  907.0 Wall Furnaces. . . . . . . . . . . . . . . . 204

  907.1 Application . . . . . . . . . . . . . . . . . . 204

  907.2 Installation . . . . . . . . . . . . . . . . . . 204

  907.3 Location . . . . . . . . . . . . . . . . . . . . 205

  907.4 Combustion and Circulating Air . . 205

  907.5 Oil-Fired Wall Furnaces . . . . . . . . 205

  908.0 Clothes Dryers . . . . . . . . . . . . . . . 205

  908.1 Application . . . . . . . . . . . . . . . . . . 205

  908.2 Electric Clothes Dryers . . . . . . . . . 205

  908.3 Gas-Fired Clothes Dryers. . . . . . . 205

  909.0 Conversion Burners . . . . . . . . . . . 205

  909.1 General. . . . . . . . . . . . . . . . . . . . . 205

  910.0 Burner Assemblies . . . . . . . . . . . . 206

  910.1 Oil Burners . . . . . . . . . . . . . . . . . . 206

  910.2 Gas Burners . . . . . . . . . . . . . . . . . 206

  911.0 Decorative Appliances for Installation in Vented Fireplaces. . . 206

• CMC § 503.5 Medium relevance — show source text

  (1) DX and chilled-water cooling units that control the capacity of the mechanical cooling directly based on space temperature shall have a minimum of two stages of fan control. Low or minimum speed shall not exceed 66 percent of full speed. At low or minimum speed, the fan system shall draw no more than 40 percent of the fan power at full fan speed. Low or minimum speed shall be used during periods of low cooling load and ventilation-only operation.

  (2) All other units, including DX cooling units and chilled-water units that control the space temperature by modulating the airflow to the space, shall have modulating fan control. Minimum speed shall not exceed 50 percent of full speed. At minimum speed, the fan system shall draw no more than 30 percent of the power at full fan speed. Low or minimum speed shall be used during periods of low cooling load and ventilation-only operation.

  (3) Units that include an air economizer to meet the requirements of Section E 503.5 through Section E 503.5.4.1 shall have a minimum of two speeds of fan control during economizer operation.

  Exceptions:

  (1) Modulating fan control shall not be required for chilled-water and evaporative cooling units with less than 1 hp (0.7 kW) fan motors where the units are not used to provide ventilation air and where the indoor fan cycles with the load.

  (2) Where the volume of outdoor air required to meet the ventilation requirements of Chapter 4 or ASHRAE 62.1 at low speed exceeds the air that would be delivered at the speed defined in Section E 503.5.6.2(1), or Section E 503.5.6.2(2), then the minimum speed shall be selected to provide the required ventilation air.

  [ASHRAE 90.1:6.5.3.2.1]

  TABLE E 503.5.6.2

  FAN AIRFLOW CONTROL

  [ASHRAE 90.1: TABLE 6.5.3.2.1]

  COOLING SYSTEM TYPE	FAN MOTOR SIZE, (hp)	MECHANICAL COOLING CAPACITY, (Btu/h)
  DX cooling	Any	≥65 000
  Chilled-water and evapo- rative cooling	≥1⁄4	Any

  For SI units: 1000 British thermal units per hour = 0.293 kW, 1 horsepower = 0.746 kW, 1 cubic foot per minute = 0.00047 m [3] /s

  E 503.5.6.2.1 VAV Static Pressure Sensor Location. Static pressure sensors used to control VAV fans shall be located such that the controller setpoint is not more than 1.2 inches water column (0.30 kPa). Where this results in the sensor being located downstream of major duct splits, sensors shall be installed in each major branch to ensure that static pressure is maintained in each.

  Exception: Systems that are in accordance with Section E 503.5.6.2.2. [ASHRAE 90.1:6.5.3.2.2]

• CMC § 911.2 Medium relevance — show source text

  911.2 Prohibited Installations . . . . . . . . . 206

  911.3 Installation . . . . . . . . . . . . . . . . . . 206

  911.4 Fireplace Screens. . . . . . . . . . . . . 206

  912.0 Gas Fireplaces, Vented . . . . . . . . 206

  912.1 Application . . . . . . . . . . . . . . . . . . 206

  912.2 Reserved . . . . . . . . . . . . . . . . . . . 206

  912.3 Installation . . . . . . . . . . . . . . . . . . 206

  912.4 Combustion and Circulating Air . . . 206

  913.0 Factory-Built Fireplaces and Fireplace Stoves. . . . . . . . . . . . . . 206

  913.1 Factory-Built Fireplaces . . . . . . . . 206

  913.2 Fireplace Stoves. . . . . . . . . . . . . . 206

  913.3 Fireplace Accessories . . . . . . . . . 206

  914.0 Non-Recirculating Direct Gas-Fired Industrial Air Heaters. . . 206

  914.1 Application . . . . . . . . . . . . . . . . . . 206

  914.2 Prohibited Installations . . . . . . . . . 206

  914.3 Installation . . . . . . . . . . . . . . . . . . 206

  914.4 Clearance from Combustible

  Materials . . . . . . . . . . . . . . . . . . . . 207

  914.5 Air Supply . . . . . . . . . . . . . . . . . . . 207

  914.6 Atmospheric Vents, Gas Reliefs, or Bleeds . . . . . . . . . . . . . 207

  914.7 Relief Openings . . . . . . . . . . . . . . 207

  914.8 Purging . . . . . . . . . . . . . . . . . . . . . 207

  915.0 Room Heaters . . . . . . . . . . . . . . . 207

  915.1 Application . . . . . . . . . . . . . . . . . . 207

  915.2 Electric Room Heaters . . . . . . . . . 207

  915.3 Gas-Fired Room Heaters . . . . . . . 207

  xxxvi

  915.4 Solid-Fuel Type Room Heaters . . 208

  916.0 Unit Heaters . . . . . . . . . . . . . . . . . 208

  916.1 Application . . . . . . . . . . . . . . . . . . 208

  916.2 Support . . . . . . . . . . . . . . . . . . . . 208

  916.3 Clearance for Suspended-Type Unit Heaters . . . . . . . . . . . . . . . . . 208

  916.4 Combustion and Circulating Air. . . 208

  916.5 Ductwork. . . . . . . . . . . . . . . . . . . . 208

  916.6 Installation in Commercial

  Garages and Aircraft Hangars . . . 208

• CMC § 4.15 Medium relevance — show source text

  91|AHRI 1250|July 10, 2020| |Unit cooler, low temperature,
  net capacity (qnet) ≥ 15 500 Btu/h|UC.L,
  ≥15 500 Btu/h|4.15|AHRI 1250|July 10, 2020|

  For SI units: 1000 British thermal units per hour = 0.293 kW

  • qnet is net capacity (Btu/h) as determined in accordance with AHRI 1250.

  2025 CALIFORNIA MECHANICAL CODE 473

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  APPENDIX E

  Col1	TABLE E 503.7.2 MINIMUM DUCT INSULATION R-VALUE1 [ASHRAE 90.1: TABLE 6.8.2]	Col3	Col4
  CLIMATE ZONE	DUCT LOCATION	DUCT LOCATION	DUCT LOCATION
  CLIMATE ZONE	EXTERIOR2	UNCONDITIONED SPACE AND BURIED DUCTS	INDIRECTLY CONDITIONED SPACE3, 4
  SUPPLY AND RETURN DUCTS FOR HEATING AND COOLING	SUPPLY AND RETURN DUCTS FOR HEATING AND COOLING	SUPPLY AND RETURN DUCTS FOR HEATING AND COOLING	SUPPLY AND RETURN DUCTS FOR HEATING AND COOLING
  0 to 4	R-8	R-6	R-1.9
  5 to 8	R-12	R-6	R-1.9
  SUPPLY AND RETURN DUCTS FOR HEATING ONLY	SUPPLY AND RETURN DUCTS FOR HEATING ONLY	SUPPLY AND RETURN DUCTS FOR HEATING ONLY	SUPPLY AND RETURN DUCTS FOR HEATING ONLY
  0 to 1	none	none	none
  2 to 4	R-6	R-6	R-1.9
  5 to 8	R-12	R-6	R-1.9
  SUPPLY AND RETURN DUCTS FOR COOLING ONLY	SUPPLY AND RETURN DUCTS FOR COOLING ONLY	SUPPLY AND RETURN DUCTS FOR COOLING ONLY	SUPPLY AND RETURN DUCTS FOR COOLING ONLY
  0 to 6	R-8	R-6	R-1.9
  7 to 8	R-1.9	R-1.9	R-1.9

  Notes: 1 Insulation R-values, measured in [°F•h•ft 2 /(Btu•in)] [(m•K)/W], are for the insulation as installed and do not include film resistance. The required minimum thicknesses do not consider water vapor transmission and possible surface condensation. Where portions of the building envelope are used as a plenum enclosure, building envelope insulation shall be as required by the most restrictive condition of Section E 503.4.7.1 or ASHRAE 90.1, depending on whether the plenum is located in the roof, wall, or floor. Insulation resistance measured on a horizontal plane in accordance with ASTM C518 at a mean temperature of 75°F (24°C) at the installed thickness. 2 Includes attics above insulated ceilings, parking garages and crawl spaces. 3 Includes return air plenums, with or without exposed roofs above.

• CMC § 909.21.1.1 Medium relevance — show source text

  909.21.1.1 Use of ventilation systems. Ventilation systems, other than hoistway supply air systems, are permitted to be used to exhaust air from adjacent spaces on the fire floor, two floors immediately below and one floor immediately above the fire floor to the building’s exterior where necessary to maintain positive pressure relationships as required in Section 909.21.1 during operation of the elevator shaft pressurization system.

  909.21.2 Rational analysis. A rational analysis complying with Section 909.4 shall be submitted with the construction documents.

  909.21.3 Ducts for system. Any duct system that is part of the pressurization system shall be protected with the same fire-resistance rating as required for the elevator shaft enclosure.

  909.21.4 Fan system. The fan system provided for the pressurization system shall be as required by Sections 909.21.4.1 through 909.21.4.4.

  909.21.4.1 Fire resistance. Where located within the building, the fan system that provides the pressurization shall be protected with the same fire-resistance rating required for the elevator shaft enclosure.

  909.21.4.2 Smoke detection. The fan system shall be equipped with a smoke detector that will automatically shut down the fan system when smoke is detected within the system.

  909.21.4.3 Separate systems. A separate fan system shall be used for each elevator hoistway.

  909.21.4.4 Fan capacity. The supply fan shall be either adjustable with a capacity of not less than 1,000 cubic feet per minute (0.4719 m [3] /s) per door, or that specified by a registered design professional to meet the requirements of a designed pressurization system.

  909.21.5 Standby power. The pressurization system shall be provided with standby power in accordance with Section 2702.

  909.21.6 Activation of pressurization system. The elevator pressurization system shall be activated upon activation of the elevator lobby smoke detectors.

  909.21.7 Testing. Testing for performance shall be required in accordance with Section 909.18.8. System acceptance shall be in accordance with Section 909.19.

  909.21.8 Marking and identification. Detection and control systems shall be marked in accordance with Section 909.14.

  909.21.9 Control diagrams. Control diagrams shall be provided in accordance with Section 909.15.

  909.21.10 Control panel. A control panel complying with Section 909.16 shall be provided.

  909.21.11 System response time. Hoistway pressurization systems shall comply with the requirements for smoke control system response time in Section 909.17.

  SECTION 910—SMOKE AND HEAT REMOVAL

  [F] 910.1 General. Where required by this code, smoke and heat vents or mechanical smoke removal systems shall conform to the requirements of this section.

  2025 CALIFORNIA BUILDING CODE 9-51

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

  FIRE PROTECTION AND LIFE SAFETY SYSTEMS

  [F] 910.2 Where required. Smoke and heat vents or a mechanical smoke removal system shall be installed as required by Sections 910.2.1 and 910.2.2.

• CMC § 204.0 Medium relevance — show source text

  0
  204.0
  206.0
  207.0
  208.0
  209.0
  210.0
  214.0
  215.0
  216.0
  217.0
  222.0
  223.0
  228.0
  |||X|X|X|||||X|X|X|X|X|X|X||||||||| |Adopting Agency
  Adopt Entire Chapter
  Adopt Entire Chapter as
  amended (amended sections
  listed below)
  Adopt only those sections
  that are listed below
  Chapter/Section
  203.0
  204.0
  206.0
  207.0
  208.0
  209.0
  210.0
  214.0
  215.0
  216.0
  217.0
  222.0
  223.0
  228.0
  ||||||||||X||X|X|X|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.

  2025 CALIFORNIA MECHANICAL CODE 29

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  30 2025 CALIFORNIA MECHANICAL CODE

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  CHAPTER 2

  DEFINITIONS

  201.0 General.

  201.1 Applicability. For the purpose of this code, the following terms have the meanings indicated in this chapter.

  No attempt is made to define ordinary words, which are used in accordance with their established dictionary meanings, except where a word has been used loosely, and it is necessary to define its meaning as used in this code to avoid misunderstanding.

  202.0 Definition of Terms.

  202.1 General. The definitions of terms are arranged alphabetically according to the first word of the term.

  203.0 – A –

  Absorption Unit. An absorption refrigeration system that has been factory-assembled and tested prior to its installation.

  Accepted Engineering Practice. That which conforms to technical or scientific-based principles, test, or standards that are accepted by the engineering profession.

  Access Panel. A closure device used to cover an opening into a duct, an enclosure, equipment, or an appurtenance.

  [NFPA 96:3.3.1]

  Accessible. Where applied to a device, appliance, or equipment, “accessible” means having access thereto, but which first may require the removal of an access panel, door, or similar obstruction.

  Accessible, Readily. Having a direct access without the necessity of removing a panel, door, or similar obstruction.

• CMC § 907.0 Medium relevance — show source text

  TABLE OF CONTENTS

  907.0 Wall Furnaces. . . . . . . . . . . . . . . . 204

  907.1 Application . . . . . . . . . . . . . . . . . . 204

  907.2 Installation . . . . . . . . . . . . . . . . . . 204

  907.3 Location . . . . . . . . . . . . . . . . . . . . 205

  907.4 Combustion and Circulating Air . . 205

  907.5 Oil-Fired Wall Furnaces . . . . . . . . 205

  908.0 Clothes Dryers . . . . . . . . . . . . . . . 205

  908.1 Application . . . . . . . . . . . . . . . . . . 205

  908.2 Electric Clothes Dryers . . . . . . . . . 205

  908.3 Gas-Fired Clothes Dryers. . . . . . . 205

  909.0 Conversion Burners . . . . . . . . . . . 205

  909.1 General. . . . . . . . . . . . . . . . . . . . . 205

  910.0 Burner Assemblies . . . . . . . . . . . . 206

  910.1 Oil Burners . . . . . . . . . . . . . . . . . . 206

  910.2 Gas Burners . . . . . . . . . . . . . . . . . 206

  911.0 Decorative Appliances for Installation in Vented Fireplaces. . . 206

  911.1 Application . . . . . . . . . . . . . . . . . . 206

  911.2 Prohibited Installations . . . . . . . . . 206

  911.3 Installation . . . . . . . . . . . . . . . . . . 206

  911.4 Fireplace Screens. . . . . . . . . . . . . 206

  912.0 Gas Fireplaces, Vented . . . . . . . . 206

  912.1 Application . . . . . . . . . . . . . . . . . . 206

  912.2 Reserved . . . . . . . . . . . . . . . . . . . 206

  912.3 Installation . . . . . . . . . . . . . . . . . . 206

  912.4 Combustion and Circulating Air . . . 206

  913.0 Factory-Built Fireplaces and Fireplace Stoves. . . . . . . . . . . . . . 206

  913.1 Factory-Built Fireplaces . . . . . . . . 206

  913.2 Fireplace Stoves. . . . . . . . . . . . . . 206

  913.3 Fireplace Accessories . . . . . . . . . 206

  914.0 Non-Recirculating Direct Gas-Fired Industrial Air Heaters. . . 206

  914.1 Application . . . . . . . . . . . . . . . . . . 206

  914.2 Prohibited Installations . . . . . . . . . 206

  914.3 Installation . . . . . . . . . . . . . . . . . . 206

  914.4 Clearance from Combustible

  Materials . . . . . . . . . . . . . . . . . . . . 207

• CMC § 25.4 Medium relevance — show source text

  
  86
  151
  196
  222
  244
  287|4934
  3409
  3380
  3332
  3285
  3239
  3150|2550
  2125
  2102
  2064
  2026
  1987
  1910| |100|0
  2
  5
  10
  15
  20
  30
  50|0
  21
  60
  80
  93
  105
  131
  197|1411
  1155
  1141
  1118
  1095
  1073
  1029
  944|770
  700
  692
  679
  666
  653
  627
  575|0
  25
  71
  94
  109
  122
  149
  217|1908
  1536
  1519
  1492
  1465
  1438
  1387
  1288|1040
  935
  926
  910
  895
  880
  849
  787|0
  30
  82
  108
  126
  141
  170
  241|2491
  1975
  1955
  1923
  1892
  1861
  1802
  1688|1310
  1170
  1159
  1142
  1124
  1107
  1071
  1000|0
  44
  107
  142
  163
  181
  215
  292|3925
  3027
  3002
  2961
  2920
  2880
  2803
  2657|2050
  1820
  1803
  1775
  1747
  1719
  1663
  1550|0
  72
  136
  180
  206
  226
  265
  350|5729
  4313
  4282
  4231
  4182
  4133
  4037
  3856|2950
  2550
  2531
  2500
  2469
  2438
  2375
  2250|

  For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m [2]

  2025 CALIFORNIA MECHANICAL CODE 173

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  CHIMNEYS AND VENTS

  TABLE 803.1.2(1) TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(a)] (continued)

  Col1	Col2	Col3	Col4	Col5	NUMBER OF APPLIANCES:	Col7	Col8	Col9	Col10	Col11	SINGLE	Col13	Col14	Col15	Col16	Col17
  					APPLIANCE TYPE:	APPLIANCE TYPE:	APPLIANCE TYPE:	APPLIANCE TYPE:	**APPLIANCE

• CMC § 1220.4.2 Medium relevance — show source text

  8|1220.4.2 – 1220.4.6| |1221.7|1221.6| |1308.2 – 1308.4.1|1308.3 – 1308.5.1| |Table 1308.3.1|Table 1308.4.1| |1308.4.2|1308.5.2| |1308.4.2.2 – 1308.6.4|1308.5.2.1 – 1308.7.3| |Table 1308.4.6.2|Table 1308.5.6.2| |1308.6.5 – 1308.13.1|1308.7.7 – 1308.14.1| |1312.1.2 – 1312.1.3|1312.1.1 – 1312.1.2| |Chapter 17|Appendix F| |Chapter 18|Chapter 17| |D 103.2|D 103.1| |E 503.5.6.7|E 503.5.6.6| |E 503.5.7.2 – E 503.5.7.6|E 503.5.7.1 – E 503.5.7.5| |Table E 503.5.7.2|Table E 503.5.7.1| |Table E 503.5.7.6|Table E 503.5.7.5| |Table E 503.5.10.1.2(1)|Table E 503.5.10(1)| |Table E 503.5.10.1.2(2)|Table E 503.5.10(2)| |E 503.5.10.1.2|E 503.5.10| |E 503.5.10.2 – E 503.5.10.2.2|E 503.5.10.1 – E 503.5.10.1.2| |E 503.5.12.1|E 503.5.12| |E 503.5.12.2|E 503.5.12.1| |E 503.6.5.4|E 503.6.5.4.1|

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