75

601.0 Scope.601.1 Ducts and plenums that are portions of aheating, cooling, absorption or evaporative cooling,or product-conveying system shall comply with therequirements of this chapter.601.2 Sizing Requirements. Duct systems usedwith blower-type equipment that are portions of aheating, cooling, absorption, evaporative cooling, oroutdoor-air ventilation system shall be sized inaccordance with Chapter 17, or by other approvedmethods.

602.0 Material.602.1 General. Supply air, return air, and outside airfor heating, cooling, or evaporative cooling systemsshall be conducted through duct systems constructedof metal as set forth in Tables 6-1, 6-2, 6-3, 6-4, 6-7, 6-8, 6-9, and 6-10, or metal ducts complying with UMCStandard No. 6-2 or the referenced HVAC ductconstruction standard in Chapter 17. Rectangularducts in excess of two (2) inches w.g. shall complywith UMC Standard No. 6-2 or the referenced HVACduct construction standard in Chapter 17. Ducts,plenums, and fittings may be constructed ofconcrete, clay, or ceramics when installed in theground or in a concrete slab, provided the joints aretightly sealed.

Corridors shall not be used to convey air to orfrom rooms if the corridor is required to be of fire-resistive construction per the Building Code.

Concealed building spaces or independentconstruction within buildings may be used as ductsor plenums.

When gypsum products are exposed in ducts orplenums, the air temperature shall be restricted to arange from 50ºF (10ºC) to 125ºF (52ºC), and moisturecontent shall be controlled so that the material is notadversely affected. For the purpose of this section,gypsum products shall not be exposed in ductsserving as supply from evaporative coolers, and inother air-handling systems regulated by this chapterwhen the temperature of the gypsum product will bebelow the dew point temperature.

See Chapter 8 for limitations on combustionproducts venting systems extending into or throughducts or plenums.

See Chapter 5 for limitations on environmentalair systems exhaust ducts extending into or throughducts or plenums.

Exhaust ducts under positive pressure andventing systems shall not extend into or passthrough ducts or plenums. For appliance vents andchimneys, see Chapter 8.602.2 Combustibles Within Ducts or Plenums.Materials exposed within ducts or plenums shall benoncombustible or shall have a flame spread indexnot greater than twenty-five (25) and a smoke devel-oped index not greater than fifty (50), when tested asa composite product in accordance with one of thefollowing test methods: NFPA 255, Method of Test ofSurface Burning Characteristics of Building Materials,ASTM E84, Surface Burning Characteristics of BuildingMaterials, or UL 723, Test for Surface Burning Charac-teristics of Building Materials, except as indicatedbelow.

Exceptions:(1) Return-air and outside-air ducts, plenums,

or concealed spaces that serve a dwellingunit shall be permitted to be of combustibleconstruction.

(2) Air filters meeting the requirements ofSections 311.2 and 503.3.

(3) Water evaporation media in an evaporativecooler.

(4) Charcoal filters when protected with anapproved fire suppression system.

(5) Electrical wiring in plenums shall complywith NFPA 70, National Electrical Code. Elec-trical wires and cables and optical fibercables shall be listed and labeled as suitablefor use in plenums and shall have a flamespread distance not greater than five (5) feet(1,524 mm), an average optical density notgreater than 0.15, and a peak optical densitynot greater than 0.5, when tested in accor-dance with NFPA 262, Flame Travel andSmoke of Wires and Cables for Use in Air-Handling Spaces.

(6) Nonmetallic fire sprinkler piping inplenums shall be listed and labeled as suit-able for use in plenums and shall have aflame spread distance not greater than five(5) feet (1,524 mm), an average opticaldensity not greater than 0.15 and, a peakoptical density not greater than 0.5, whentested in accordance with UL 1887, Fire Testof Plastic Sprinkler Pipe for Visible Flame andSmoke Characteristics.

CHAPTER 6DUCT SYSTEMS

(7) Nonmetallic pneumatic tubing in plenumsshall be listed and labeled as suitable for usein plenums and shall have a flame spreaddistance not greater than five (5) feet (1,524mm), an average optical density not greaterthan 0.15, and a peak optical density notgreater than 0.5, when tested in accordancewith UL 1820, Fire Test of Pneumatic Tubingfor Flame and Smoke Characteristics.

(8) Loudspeakers and recessed lighting fixtures,including their assemblies and accessories, inplenums shall be listed and labeled as suit-able for use in plenums and shall have a peakrate of heat release not greater than 100 kilo-watts, an average optical density not greaterthan 0.15, and a peak optical density notgreater than 0.5, when tested in accordancewith UL 2043, Fire Test for Heat and VisibleSmoke Release for Discrete Products and theirAccessories Installed in Air-Handling Spaces.

(9) Smoke detectors.(10) Duct insulation, coverings, and linings and

other supplementary materials complyingwith 605.0.

(11) Materials in a Group H, Division 6, fabrica-tion area including the areas above andbelow the fabrication area sharing acommon air recirculation path with thefabrication area.

602.3 Factory-Made Air Ducts. Factory-made airducts shall be approved for the use intended or shallconform to the requirements of the referenced stan-dard for air ducts in Chapter 17. Each portion of afactory-made air duct system shall be identified bythe manufacturer with a label or other suitable iden-tification indicating compliance with the referencedstandard for air ducts in Chapter 17 and its classdesignation. These ducts shall be listed and shall beinstalled in accordance with the terms of their listingand the requirements of UMC Standard No. 6-5.Flexible air connectors are not permitted.602.4 Joints and Seams of Ducts. Joints of ductsystems shall be made substantially air-tight bymeans of tapes, mastics, gasketing, or other means.

Crimp joints for round ducts shall have a contactlap of at least 1-1/2 inch (38 mm) and shall bemechanically fastened by means of at least three (3)sheet-metal screws equally spaced around the joint,or an equivalent fastening method.

Joints and seams for 0.016 inch (0.41 mm) (No. 28gauge) and 0.013 inch (0.33 mm) (No. 30 gauge) resi-dential rectangular ducts shall be as specified in Table6-1 for 0.019 inch (0.48 mm) (No. 26 gauge) material.

Joints and seams for rectangular duct systemsshall be as specified in Table 6-1.

Joints and seams for flat oval ducts and roundducts in other than single-dwelling units shall be asspecified in Table 6-8.

Joints and seams and all reinforcements forfactory-made air ducts and plenums shall meet withthe conditions of prior approval in accordance withthe installation instructions that shall accompany theproduct. Closure systems for rigid air ducts andplenums shall be listed in accordance with UL 181A,Standard for Closure Systems for Use with Rigid AirDucts and Air Connectors. Closure systems for flexibleair ducts shall be listed in accordance with UL 181B,Standard for Closure Systems for Use with Flexible AirDucts and Air Connectors.602.5 Metal. Every duct, plenum, or fitting of metalshall comply with Table 6-1 or 6-8.

Exceptions:(1) Ducts, plenums, and fittings for systems

serving single-dwelling units may complywith Table 6-9.

(2) Duct systems complying with UMC Stan-dard No. 6-2 or the referenced HVAC ductconstruction standard in Chapter 17, withprior approval, or duct systems complyingwith UL 181, Standard for Factory-Made AirDucts and Air Connectors.

(3) Duct systems complying with the UMCStandard No. 6-2 or the referenced HVACduct construction standard in Chapter 17,with prior approval.

602.6 Tin. Existing tin ducts may be used whencooling coils are added to a heating system, providedthe first ten (10) feet (3,048 mm) of the duct orplenum measured from the cooling coil dischargeare constructed of metal of the gauge thickness setforth in Tables 6-1, 6-8, or 6-9 of this chapter or are ofapproved material and construction. Tin ductscompletely enclosed in inaccessible concealed areasneed not be replaced. All accessible ducts shall beinsulated to comply with Table 6-6 of this chapter.For the purpose of this subsection, ducts shall beconsidered accessible where the access space is thirty(30) inches (762 mm) or greater in height.602.7 Vibration Isolators. Vibration isolatorsinstalled between mechanical equipment and metalducts (or casings) shall be made of an approvedmaterial and shall not exceed ten (10) inches (254mm) in length.

603.0 Quality of Material.Galvanized steel shall be of lock-forming qualitywith a minimum coating of 1.25 ounces of zinc persquare foot (0.04 kg/m3) conforming to the require-ments of UMC Standard No. 2-2.

UNIFORM MECHANICAL CODE

76

602.2 – 603.0

604.0 Installation of Ducts.604.1 General Ducts Under Floor or Crawl Space.Air ducts installed under a floor in a crawl spaceshall be installed as follows:(A) Shall not prevent access to any area of the crawl

space.(B) Where it is required to move under ducts for

access to areas of the crawl space a minimumvertical clearance of eighteen (18) inches (457mm) shall be provided.

604.2 Metal Ducts. Ducts shall be securely fastenedin place at each change of direction and as set forthin Table 6-7. Vertical rectangular ducts and verticalround ducts shall be supported as set forth in Table6-7, Part A. Riser ducts shall be held in place bymeans of metal straps or angles and channels tosecure the riser to the structure.

Metal ducts shall be installed with at least four(4) inches (102 mm) separation from earth. Metalducts when installed in or under a concrete slab shallbe encased in at least two (2) inches (51 mm) ofconcrete.

Ducts shall be installed in a building withadequate clearance so as to permit retaining the fullthickness of fireproofing on structural members.

Supports for rectangular ducts as set forth inTable 6-7, when suspended from above, shall beinstalled on two opposite sides of each duct and shallbe riveted, bolted, or metal screwed to each side ofthe duct at not more than the intervals specified.

Horizontal round ducts forty (40) inches (1,016mm) or less in diameter when suspended from aboveshall be supported at intervals not more than as setforth in Table 6-7 with one hanger installed tocomply with the requirements listed below:

604.2.1 Ducts shall be equipped with tight-fitting circular bands extending around theentire perimeter of the duct at each specifiedsupport interval.604.2.2 Circular bands shall be not less than one(1) inch (25 mm) wide nor less than equivalent tothe gauge of the duct material it supports.

Exception: Ducts ten (10) inches (254 mm)and less in diameter may be supported byNo. 18 gauge galvanized steel wire.

604.2.3 Each circular band shall be providedwith a suitable means of connecting to thesuspending support.604.2.4 Ducts shall be braced and guyed toprevent lateral or horizontal swing.

604.3 Factory-Made Air Ducts. Listed Class 0 orClass 1 factory-made air ducts may be installed inany occupancy covered by this code.

Factory-made air ducts shall not be used forvertical risers in air-duct systems serving more thantwo stories. Such ducts shall not penetrate construc-tion where fire dampers are required.

Factory-made air ducts shall be installed with atleast four (4) inches (102 mm) of separation fromearth, except when installed as a liner inside ofconcrete, tile, or metal pipe; they shall be protectedfrom physical damage.

The temperature of the air to be conveyed in anyof these classes of ducts shall not exceed 250ºF(122ºC).604.4 Protection of Ducts. Ducts installed in loca-tions where they are exposed to mechanical damageby vehicles or from other causes shall be protectedby approved barriers.604.5 Support of Ducts. Installers shall provide themanufacturer’s field fabrication and installationinstructions.

In the absence of specific supporting materialsand spacing, approved factory-made air ducts maybe installed as set forth in Table 6-10.604.6 Protection Against Flood Damage. In floodhazard areas, ducts shall be located above the designflood elevation or shall be designed and constructedto prevent water from entering or accumulatingwithin the ducts during floods up to the design floodelevation. If the ducts are located below the designflood elevation, the ducts shall be capable of resistinghydrostatic and hydrodynamic loads and stresses,including the effects of buoyancy, during the occur-rence of flooding to the design flood elevation.

605.0 Insulation of Ducts.Supply-, return-air ducts and plenums of a heatingor cooling system shall be insulated to achieve theminimum thermal (R) value as set forth in Tables 6-6A and B.

Exceptions:(A) Factory-installed plenums, casings, or duct-

work furnished as a part of HVAC equip-ment tested and rated in accordance withapproved energy efficiency standards.

(B) Ducts or plenums located in conditionedspaces.

(C) For runouts less than ten (10) feet (3,048mm) in length to air terminals or air outlets,the rated R value of insulation need notexceed R-3.5 (R-0.6).

(D) Backs of air outlets and outlet plenumsexposed to unconditioned or indirectlyconditioned spaces with face areas exceedingfive (5) square feet (0.5 m2) need not exceed

DUCT SYSTEMS 604.0 – 605.0

77

R-2 (R-0.4); those five (5) square feet (0.5 m2)or smaller need not be insulated.

(E) Ducts and plenums used exclusively forevaporative cooling systems.

Approved materials shall be installed withinducts and plenums for insulating, sound deadening,or other purposes. Materials shall have a mold,humidity, and erosion-resistant surface that meetsthe requirements of the referenced standard for airducts in Chapter 17. Duct liners in systems operatingwith air velocities exceeding 2,000 feet per minute(10.16 m/s) shall be fastened with both adhesive andmechanical fasteners, and exposed edges shall haveadequate treatment to withstand the operatingvelocity.

Insulation applied to the surface of ducts,including duct coverings, linings, tapes, and adhe-sives, located in buildings shall have a flame-spreadindex not greater than twenty-five (25) and a smokedeveloped index not greater than fifty (50), whentested in accordance with NFPA 255,Method of Test ofBurning Characteristics of Building Materials, or inaccordance with ASTM E 84, Surface Burning Charac-teristics of Building Materials, or in accordance withthe provisions of UL 723, Test for Surface BurningCharacteristics of Building Materials. The specimenpreparation and mounting procedures of ASTM E2231, Specimen Preparation and Mounting of Pipe andDuct Insulation Materials to Assess Surface BurningCharacteristics, shall be used. Air duct coverings andlinings shall not flame, glow, smolder, or smokewhen tested in accordance with ASTM C 411, Hot-Surface Performance of High-Temperature Thermal Insu-lation, at the temperature to which they are exposedin service. In no case shall the test temperature bebelow 250ºF (121ºC).

Factory-made air ducts and faced insulationsintended for installation on the exterior of ducts shallbe legibly printed with the name of the manufac-turer, the thermal resistance (R) value at installedthickness, and the flame-spread index and smokedeveloped index of the composite material.

606.0 Smoke Dampers, Fire Dampers, and CeilingDampers.606.1 Smoke Dampers. Smoke dampers shallcomply with the standards for leakage-rateddampers referenced in Chapter 17, and shall beinstalled in accordance with approved manufac-turer’s installation instructions when required by theBuilding Code. Smoke dampers shall be labeled byan approved agency.606.2 Fire Dampers. Fire dampers shall complywith the standard for fire dampers referenced in

Chapter 17, and shall be installed in accordance withthe approved manufacturer’s installation instruc-tions when required by the Building Code. Firedampers shall have been tested for closure underairflow conditions and shall be labeled for bothmaximum airflow permitted and direction of flow.When more than one damper is installed at a point ina single air path, the entire airflow shall be assumedto be passing through the smallest damper area. Firedampers shall be labeled by an approved agency.

Ductwork shall be connected to damper sleevesor assemblies in accordance with the fire dampermanufacturer’s installation instructions.606.3 Ceiling Radiation Dampers. Ceiling radiationdampers shall comply with the standard for ceilingradiation dampers referenced in Chapter 17, andshall be installed in accordance with the manufac-turer’s approved installation instructions in the fire-resistive ceiling element of floor-ceiling and roof-ceiling assemblies when required by the BuildingCode. Fire dampers not meeting the temperaturelimitation of ceiling radiation dampers shall not beused as a substitute. Ceiling radiation dampers shallbe labeled by an approved agency.606.4 Multiple Arrangements. When size requiresthe use of multiple dampers, the installation shall beframed in an approved manner to ensure that thedampers remain in place.606.5 Access and Identification. Dampers shall beprovided with an approved means of access largeenough to permit inspection and maintenance of thedamper and its operating parts. The access shall notimpair fire-resistive construction. Access shall notrequire the use of tools, keys, or special knowledge.Access points shall be permanently identified on theexterior by a label with letters not less than 1/2 inch(12.7 mm) in height reading: SMOKE DAMPER orFIRE DAMPER. Access doors in ducts shall be tightfitting and suitable for the required duct construction.606.6 Freedom from Interference. Dampers shall beinstalled in a manner to ensure positive closing oropening as required by function. Interior liners orinsulation shall be held back from portions of adamper, its sleeve, or adjoining duct that wouldinterfere with the damper’s proper operation. Exte-rior materials shall be installed so as to avoid interfer-ence with the operation or maintenance of externaloperating devices needed for proper function.606.7 Temperature Classification of OperatingElements. Fusible links, thermal sensors, and pneu-matic or electric operators shall have a temperaturerating or classification as required by the BuildingCode.

UNIFORM MECHANICAL CODE

78

605.0 – 606.7

607.0 Ventilating Ceilings.607.1 General. Perforated ceilings may be used forair supply within the limitations of this section. Exitcorridors, when required to be of fire-resistiveconstruction by the Building Code, shall not haveventilating ceilings.607.2 Requirements. Ventilating ceilings shallcomply with the following provisions:

607.2.1 Suspended ventilating ceiling materialshall have a Class I flame-spread classificationon both sides, determined in accordance withthe Building Code. Suspended ventilatingceiling supports shall be of noncombustiblematerials.607.2.2 Lighting fixtures recessed into venti-lating ceilings shall be of a type approved forthat purpose.

608.0 Use of Under-Floor Space as SupplyPlenum for Dwelling Units.An under-floor space may be used as a supplyplenum, provided:608.1 The use of under-floor space shall be limited todwelling units not more than two stories in height.Except for the floor immediately above the under-floor plenum, supply ducts shall be providedextending from the plenum to registers on otherfloor levels.

Exception: In flood hazard areas, under-floorspaces shall not be used as supply plenumsunless the flood opening requirements in theBuilding Code are satisfied.

608.2 Such spaces shall be cleaned of all loosecombustible scrap material and shall be tightly andsubstantially enclosed.608.3 The enclosing material of the under-floorspace, including the sidewall insulation, shall be notmore flammable than one (1) inch (25 mm) (nominal)wood boards (flame-spread index of 200). Installa-tion of foam plastics is regulated by the BuildingCode.608.4 Access shall be through an opening in the floorand shall be not less than twenty-four (24) inches bytwenty-four (24) inches (610 mm x 610 mm).608.5 A furnace supplying warm air to under-floorspace shall be equipped with an automatic controlthat will start the air-circulating fan when the air inthe furnace bonnet reaches a temperature not higherthan 150ºF (66ºC). Such control shall be one thatcannot be set higher than 150ºF (66ºC).608.6 A furnace supplying warm air to such spaceshall be equipped with an approved temperaturelimit control that will limit outlet air temperature to200ºF (93ºC).

608.7 A noncombustible receptacle shall be placedbelow each floor opening into the air chamber, andsuch receptacle shall conform to the following:

608.7.1 The receptacle shall be securelysuspended from the floor members and shall benot more than eighteen (18) inches (457 mm)below the floor opening.608.7.2 The area of the receptacle shall extendthree (3) inches (76 mm) beyond the opening onall sides.608.7.3 The perimeter of the receptacle shallhave a vertical lip at least one (1) inch (25.4 mm)high at the open sides if it is at the level of thebottom of the joists, or three (3) inches (76 mm)high if the receptacle is suspended.

608.8 Floor registers shall be designed for easyremoval in order to give access for cleaning thereceptacles.608.9 Exterior walls and interior stud partitions shallbe fire-stopped at the floor.608.10 Each wall register shall be connected to theair chamber by a register box or boot.608.11 A duct conforming with Section 602.0 shallextend from the furnace supply outlet at least six (6)inches (152 mm) below combustible framing.608.12 The entire ground surface of the under-floorspace shall be covered with a vapor barrier having aminimum thickness of four (4) mils (0.1016 mm) anda flame-spread index of 200 or less.608.13 Fuel-gas lines and plumbing waste cleanoutsare not located within the space.

609.0 Automatic Shutoffs.Air-moving systems supplying air in excess of 2,000cubic feet per minute (944 L/s) to enclosed spaceswithin buildings shall be equipped with an auto-matic shutoff. Automatic shutoff shall be accom-plished by interrupting the power source of the air-moving equipment upon detection of smoke in themain supply-air duct served by such equipment.Smoke detectors shall be labeled by an approvedagency for air duct installation and shall be installedin accordance with the manufacturer’s approvedinstructions. Such devices shall be compatible withthe operating velocities, pressures, temperatures,and humidities of the system. Where fire-detectionor alarm systems are provided for the building, thesmoke detectors required by this section shall besupervised by such systems.

Exceptions:(1) When the space supplied by the air-moving

equipment is served by a total coveragesmoke-detection system complying with the

DUCT SYSTEMS 607.0 – 609.0

79

Fire Code, interconnection to such systemmay be used to accomplish the requiredshutoff.

(2) Automatic shutoff is not required when alloccupied rooms served by the air-handlingequipment have direct exit to the exteriorand the travel distance does not exceed 100feet (30,480 mm).

(3) Automatic shutoff is not required for GroupR, Division 3 and Group U Occupancies.

(4) Automatic shutoff is not required forapproved smoke-control systems or whereanalysis demonstrates shutoff would createa greater hazard, such as may be encoun-tered in air-moving equipment supplyingspecialized portions of Group H Occupan-cies. Such equipment shall be required tohave smoke detection with remote indica-tion and manual shutoff capability at anapproved location.

(5) Smoke detectors that are factory installed inlisted air-moving equipment may be used inlieu of smoke detectors installed in the mainsupply-air duct served by such equipment.

UNIFORM MECHANICAL CODE

80

609.0

TABL

E6-1Du

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ctionfor4

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DUCT SYSTEMS Table 6-1

81

2”w.g

STAT

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S.ORNE

G.

INTE

RMED

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UNIFORM MECHANICAL CODE

82

Table 6-2TA

BLE6-2Du

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ctionfor5

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Duct

Leng

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ition

-1995]

2”w.g

STAT

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S.ORNE

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DUCT SYSTEMS Table 6-3 – Table 6-5

83

TABLE 6-3THICKNESS ADJUSTMENTS

Galv. Steel Ga (mm) 28 (0.48) 26 (0.55) 24 (0.70) 22 (0.78) 20 (1.00) 18 (1.31) 16 (1.61)nominalMin. Alum. equivalent1 (mm) 0.023 0.027 0.034 0.043 0.052 0.067 0.083

(0.58) (0.69) (0.86) (1.09) (1.32) (1.70) (2.11)Commercial size (mm) 0.025 0.032 0.04 0.05 0.063 0.071 0.09

(0.60) (0.80) (1.00) (1.27) (1.60) (1.80) (2.29)Lbs wt/Sf. Alum. Consult Appendix-5 for Weights

RECTANGULAR ALUMINUM DUCTADAPTED FROM 3” W.G. (750 Pa) or LOWER

Note:1Alloy 3003-H-14.

TABLE 6-4DIMENSION ADJUSTMENTS

Galv. Rigidity Class A B C D E F G H I J K LAlum. dim. per Galv. Class C E E F H I I K 1 1 1 1

Note:1Calculate an effective Ix= 3x that used for steel.

Notes:1Alloy 6061-T6 Strength normally.Any aluminum shape substitute must have a moment of inertia three times that of steel and have 30,000 psi minimum yieldstrength.

TABLE 6-5REINFORCEMENTS

Steel Angle Size,Inches (mm) Cod

Equivalent Alumn,1Angle Size, Inches Steel Bar Aluminum Bar1

1 x 1 x16 Ga.(25 x 25 x 1.61)

C 1-1/4 x 1-1/4 x 1/8(31.8 x 31.8 x 3.2)

1 x 1/8(25 x 3.2)

1-1/2 x 1/8 or 1-1/4 x 3/16(38.1 x 3.2 or 31.8 x 4.8)

1 x 1 x 1/8(25 x 25 x 3.2)

D 1-1/2 x 1-1/2 x 1/8(38.1 x 38.1 x 3.2)

1-1/2 x 1/8(38.1 x 3.2)

1-1/2 x 1/8 x or 1-1/4 x 3/16(38.1 x 3.2 or 38.1 x 4.8)

1-1/4 x 1-1/4 x 1/8(31.8 x 31.8 x 3.2)

F 1-3/4 x 1-3/4 x 1/8(44.5 x 44.5 x 3.2)

1-1/2 x 1-1/2 x 1/8(38.1 x 38.1 x 3.2)

G 2-1/2 x 2-1/2 x 1/8(63.5 x 63.5 x 3.2)

2 x 2 x 1/8(51 x 51 x 3.2)

H 2-1/2 x 2-1/2 x 3/16(63.5 x 63.5 x 4.8)

2 x 2 x 3/16(51 x 51 x 4.8)

I 2-1/2 x 2-1/2 x 3/8 or 3 x 3 x 1/4(63.5 x 63.5 x 9.5 or 76.2 x 76.2 x 6.4)

2 x 2 x 1/4(51 x 51 x 6.4)

J 2-1/2 x 2-1/2 x 3/8 or 3 x 3 x 1/4(63.5 x 63.5 x 7.9 or 76.2 x 76.2 x 6.4)

2-1/2 x 2-1/2 x 3/16(63.5 x 63.5 x 4.8)

K 3 x 3 x 3/8 or 3-1/2 x 3-1/2 x 1/4(76.2 x 76.2 x 9.5 or 88.9 x 88.9 x 6.4)

UNIFORM MECHANICAL CODE

84

Table 6-6 A

TABLE 6-6 A (I-P Units)Minimum Duct Insulation R Valuea Cooling and Heating Only Supply Ducts and Return Ductsd, e

Climate Zone Duct Location

Envelope HDD65 CDD50 Exterior Ventilated Unvented Unvented Uncon- Indirectly BuriedCriteria Table Attic Attic w/ Attic w/ ditioned Con-

Backloaded Roof Spaceb ditionedCeiling Insulationa Spacec

Heating-Only Ducts

5-1 to 5-7 0–1,800 all none none none none none none none5-8 to 5-12 1,801–3,600 all R-3.5 none none none none none none5-13 to 5-15 3,601–5,400 all R-3.5 none none none none none none5-16 to 5-18 5,401–7,200 all R-6 R-3.5 none none none none R-3.55-19 to 5-20 7,201–9,000 all R-6 R-6 R-3.5 none none none R-3.55-21 to 5-22 9,001–10,800 all R-8 R-6 R-6 none R-3.5 none R-3.55-23 10,801–12,600 all R-8 R-6 R-6 none R-6 none R-65-24 12,601–16,200 all R-8 R-8 R-6 none R-6 none R-65-25 16,201–19,800 all R-10 R-8 R-8 none R-6 none R-65-26 19,801+ all R-10 R-10 R-8 none R-8 none R-6

Cooling-Only Ducts

5-15, 18, 20, all 0–1,800 R-1.9 R-1.9 R-1.9 R-1.9 R-1.9 none none22 to 26

5-12, 14, 17, all 1,801–3,600 R-3.5 R-1.9 R-3.5 R-1.9 R-1.9 none none19, 21

5-7, 9, 11, 13, all 3,601–5,400 R-3.5 R-3.5 R-6 R-1.9 R-1.9 none none16

5-4, 6, 8, 10 all 5,401–7,200 R-6 R-6 R-6 R-3.5 R-1.9 none none5-3, 5-5 all 7,201–9,000 R-6 R-6 R-6 R-3.5 R-3.5 none R-3.55-2 all 9,001–10,800 R-6 R-6 R-8 R-3.5 R-3.5 none R-3.55-1 all 10,801+ R-8 R-8 R-8 R-3.5 R-3.5 none R-3.5

Return Ducts

5-15 to 5-26 all climates R-3.5 R-3.5 R-3.5 none none none none none

Notes:a Insulation R-values, measured in (h·ft2·ºF)/Btu, are for the insulation as installed and do not include film resistance. Therequired minimum thicknesses do not consider water vapor transmission and possible surface condensation. Where exteriorwalls are used as plenum walls, wall insulation shall be as required by the most restrictive condition. Insulation resistancemeasured on a horizontal plane in accordance with ASTM C518 at a mean temperature of 75ºF (24ºC) at the installed thickness.

b Includes crawl spaces, both ventilated and nonventilated.c Includes return-air plenums with or without exposed roofs above.d Vapor retarders shall be installed on supply ducts in spaces vented to the outside in geographic areas where the averagesummer dewpoint temperature based on the 2-1/2 percent column of dry-bulb and mean coincident wet-bulb temperatureexceeds 60ºF (16ºC).

e Insulation shall have an approved weatherproof barrier.

DUCT SYSTEMS Table 6-6 B

85

TABLE 6-6 B (I-P Units)Minimum Duct Insulation R Valuea Combined Heating and Cooling Ductsd, e

Climate Zone Duct Location

Envelope HDD65 CDD50 Exterior Ventilated Unvented Unvented Uncon- Indirectly BuriedCriteria Attic Attic w/ Attic w/ Roof ditioned ConditionedTable Backloaded Insulationa Spaceb Spacec

Ceiling5-1 0–900 10,801+ R-8 R-6 R-8 R-3.5 R-3.5 none R-3.55-2 0–900 9,001–10,800 R-6 R-6 R-8 R-3.5 R-3.5 none R-3.55-3 0–900 7,201–9,000 R-6 R-6 R-6 R-3.5 R-3.5 none R-3.55-4 0–900 0–7,200 R-6 R-3.5 R-6 R-3.5 R-1.9 none R-3.55-5 901–1,800 7,201+ R-6 R-6 R-6 R-3.5 R-3.5 none R-3.55-6 901–1,800 5,401–7,200 R-6 R-6 R-6 R-3.5 R-3.5 none R-3.55-7 901–1,800 0–5,400 R-3.5 R-3.5 R-6 R-1.9 R-1.9 none R-1.95-8 1,801–2,700 5,401+ R-6 R-6 R-6 R-3.5 R-3.5 none R-3.55-9 1,801–2,700 0–5,400 R-6 R-3.5 R-6 R-1.9 R-1.9 none R-1.95-10 2,701–3,600 5,401+ R-6 R-6 R-6 R-3.5 R-3.5 none R-3.55-11 2,701–3,600 3,601–5,400 R-6 R-6 R-6 R-3.5 R-3.5 none R-1.95-12 2,701–3,600 0–3,600 R-3.5 R-3.5 R-3.5 R-1.9 R-1.9 none R-1.95-13 3,601–5,400 3,601+ R-6 R-6 R-6 R-3.5 R-3.5 none R-3.55-14 3,601–5,400 1,801–3,600 R-6 R-3.5 R-6 R-1.9 R-3.5 none R-1.95-15 3,601–5,400 0-1,800 R-3.5 R-3.5 R-3.5 R-1.9 R-1.9 none R-1.95-16 5,401–7,200 3,601+ R-6 R-6 R-6 R-3.5 R-3.5 none R-3.55-17 5,401–7,200 1,801–3,600 R-6 R-6 R-6 R-1.9 R-3.5 none R-3.55-18 5,401–7,200 0–1,800 R-6 R-3.5 R-3.5 R-1.9 R-3.5 none R-3.55-19 7,201–9,000 1,801+ R-8 R-6 R-6 R-1.9 R-3.5 none R-3.55-20 7,201–9,000 0–1,800 R-6 R-6 R-6 R-1.9 R-3.5 none R-3.55-21 9,001–10,800 1,801+ R-8 R-6 R-6 R-1.9 R-6 none R-3.55-22 9,001–10,800 0–1,800 R-8 R-6 R-6 R-1.9 R-3.5 none R-3.55-23 10,801–12,600 all R-8 R-6 R-6 R-1.9 R-6 none R-65-24 12,601–16,200 all R-8 R-8 R-8 R-1.9 R-6 none R-65-25 16,201–19,800 all R-10 R-8 R-8 R-3.5 R-6 none R-65-26 19,801+ all R-10 R-10 R-8 R-3.5 R-8 R-3.5 R-6

Notes:a Insulation R-values, measured in (h·ft2·˚F)/Btu, are for the insulation as installed and do not include film resistance. The requiredminimum thicknesses do not consider water vapor transmission and possible surface condensation. Where exterior walls areused as plenum walls, wall insulation shall be as required by the most restrictive condition. Insulation resistance measured on ahorizontal plane in accordance with ASTM C518 at a mean temperature of 75˚F (24ºC) at the installed thickness.

b Includes crawl spaces, both ventilated and nonventilated.c Includes return air plenums with or without exposed roofs above.d Vapor retarders shall be installed on cooling supply ducts in spaces vented to the outside in geographic areas where the averagesummer dewpoint temperature based on the 2-1/2 percent column of dry-bulb and mean coincident wet-bulb temperatureexceeds 60°F (16°C).

e Insulation shall have an approved weatherproof barrier.

UNIFORM MECHANICAL CODE

86

Table 6-7

TABLE 6-7Duct Support

A. Vertical Ducts

Maximum MaximumSide of Diameter

Rectangular Metal Strap or of Round StrapDuct Angle Bracket Ducts

24" 1" x 1/8" strap1 10" 0.047" (No. 18 gauge)galvanized steel 2" wide1

36" 1" x 1" x 1/8" angle1 20" 0.058" (No. 16 gauge)galvanized steel 2" wide1

48" 1-1/8" x 1-1/8" x 1/8" angle1 40" 1/8" steel x 1-1/2"1

60" 1-1/2" x 1-1/2" x 1/8" angle1 60" 1/8" steel x 2"1

Over 60" 2" x 2" x 1/8" angle1 Over 60" 3/16" steel x 2"1

B. Horizontal Ducts

18" 1" x 18 gauge2 Same gauge as galvanized steel duct,10" 1" wide or (No. 18 gauge galvanized

30" 1" x 18 gauge2 steel wire) on 10’ centers

48" 1" x 1/8"2 20" Same gauge as galvanized steelduct, 1" wide or (No. 8 gauge

60" 1" x 1/8"2 galvanized steel wire) tied to40" 1" galvanized steel band

80" 1" x 1/8"2 around duct on 10’ centers

60" Same gauge as galvanized steelduct, 1-1/2" wide on 6' centers

Over 60" Same gauge as galvanized steelduct, 1-1/2" wide on 4' centers

C. Horizontal Ducts –– Trapeze-Type Supports

MaximumDiameter of Round HorizontalDuct or Side of Support Hanger

Rectangular Duct Angle3

36" 1-1/2" x 1-1/2" x 1/8" 1/4" round rod or 1" x 1" x 1/8" angle

48" 2" x 2" x 1/8" 1/4" round rod or 1" x 1" x 1/8" angle

60" 2" x 2" x 1/8" 5/16" round rod or 1" x 1" x 1/8" angle

84" 2" x 2" x 1/8" 3/8" round rod or 1" x 1" x 1/8" angle

Notes:1 Spaced vertically not more than 12 feet on centers.2 Spaced horizontally not more than 10 feet on centers.3 Spaced not more than 8 feet on centers.1 in. = 25.4 mm, 1 ft. = 0.305 m

DUCT SYSTEMS Table 6-8 – Table 6-9

87

Aluminum STEEL –– THICKNESS IN INCHESB. & S. Gage (STEEL –– GALVANIZED SHEET GAUGE) GIRTH JOINTS1

Duct Diameter Pressure < 2" W.C. Pressure < 2" W.C.2 Pressure > 2" < 10" W.C. Minimum GirthMax. Width Spiral Longitudinal Welded Reinforcing, Maximum(In Inches) Round Round Flat-Oval Seam Seam Fittings Pressure > 2" < 10" W.C. Spacing and Angle Size

Up to 9 24 0.019 0.024 0.019 0.024 0.030 2" Slip None(26) (24) (26) (24) (22)

Over 9 24 0.019 0.024 0.024 0.030 0.036 4" Slip NoneUp to 14 (26) (24) (24) (22) (20)

Over 14 22 0.024 0.030 0.024 0.030 0.036 4" Slip NoneUp to 23 (24) (22) (24) (22) (20)

Over 23 20 0.030 0.036 0.030 0.036 0.036 4" Slip NoneUp to 37 (22) (20) (22) (20) (20)

Over 37 18 0.036 0.047 0.036 0.036 0.047 1-1/4" x 1-1/4" x 1/8" 1-1/4" x 1-1/4" x 1/8"Up to 51 (20) (18) (20) (20) (18) Flange on 72"Over 51 16 0.047 0.058 X 0.047 0.047 1-1/4" x 1-1/4" x 1/8" 1-1/4" x 1-1/4" x 1/8"Up to 61 (18) (16) (18) (18) Flange on 72"

Over 61 14 0.058 0.070 X 0.058 0.058 1-1/2" x 1-1/2" x 1/8" 1-1/2" x 1-1/2" x 1/8"Up to 84 (16) (14) (16) (16) Flange on 48"

Notes:1 For pressure < 2 inches W.C., any of the following joints are acceptable: butt slip; pipe slip; pipe lock; roll slip; snap slip; plenumlock; and companion flange.

2 Acceptable longitudinal seams for pressure < 2 inches W.C.: Acme (grooved); snap lock; standing; and spiral.1 in. = 25.4 mm, 1 in. W.C. = 0.249 kPa

TABLE 6-8Construction Details for Round and Flat-Oval Ducts

TABLE 6-9Thickness of Metal Ducts and Plenums Used for Heating or Cooling for a Single-Dwelling Unit

GALVANIZED STEEL

Minimum Equivalent ApproximateThickness, Galvanized Sheet AluminumInches (mm) Gauge No. B.&S. Gauge

Round ducts and enclosedrectangular ducts14" (356 mm) or less 0.013 (0.33) 30 26Over 14" (356 mm) 0.016 (0.41) 28 24

Exposed rectangular ducts14" (356 mm) or less 0.016 (0.41) 28 24Over 14" (356 mm) 0.019 (0.48) 26 22

UNIFORM MECHANICAL CODE

88

Table 6-10

TABLE 6-10Alternate Supports for Factory-Made Air Ducts

Maximum SupportClass 1 Duct Material Minimum Support Material Spacing, Feet

Rigid round fibrous No. 26 gauge x 5/8" 6wide galvanized iron strap

Corrugated metal No. 18 gauge galvanized 6iron wire

Flexible No. 26 gauge x 1-1/2" 4wide galvanized iron strap

Note: 1 in. = 25.4 mm, 1 ft. = 0.305 m