CHAPTER 6 DUCT SYSTEMS

CHAPTER 6 DUCT SYSTEMS 601.0 Scope General. 601.1 General Applicability. Ducts and plenums that are portions of a heating, cooling, absorption or evaporative cooling, or product-conveying system shall comply be in accordance with the requirements of this chapter. 601.2 Sizing Requirements. Duct systems used with blower-type equipment that are portions of a heating, cooling, absorption, evaporative cooling, or outdoor-air ventilation system shall be sized in accordance with Chapter 17, or by other approved methods. 602.0 Material. 602.1 General. Supply air, return air, and outside air for heating, cooling, or evaporative cooling systems shall be conducted through duct systems constructed of metal as set forth in accordance with Table 602.1(a) through 602.1(d), Table 602.1(f) through Table 602.1(h), and Table 604.2 or SMACNA HVAC Duct Construction Standards - Metal and Flexible. Rectangular ducts exceeding 2 inches (51 mm) w.g. shall comply with SMACNA HVAC Duct Construction Standards - Metal and Flexible. Ducts, plenums, and fittings shall be permitted to be constructed of concrete, clay, or ceramics when where installed in the ground or in a concrete slab, provided the joints are tightly sealed. Corridors shall not be used to convey air to or from rooms if where the corridor is required to be of fire-resistive construction per in accordance with the building code. Concealed building spaces or independent construction within buildings shall be permitted to be used as ducts or plenums. Where gypsum products are exposed in ducts or plenums, the air temperature shall be restricted to a range from 50ºF (10ºC) to 125ºF (52ºC), and moisture content shall be controlled so that the material is not adversely affected. For the purpose of this section, gypsum products shall not be exposed in ducts serving as supply from evaporative coolers, and in other air-handling systems regulated by this chapter where the temperature of the gypsum product will be below the dew point temperature. See Chapter 8 for limitations on combustion products venting systems extending into or through ducts or plenums. See Chapter 5 for limitations on environmental air systems exhaust ducts extending into or through ducts or plenums. 602.2 Combustibles Within Ducts or Plenums. Materials exposed within ducts or plenums shall be noncombustible or shall have a flame spread index not greater than to exceed twenty-five (25) and a smoke developed index not greater than to exceed fifty (50), when where tested as a composite product in accordance with one of the following test methods: NFPA 255, ASTM E 84 or UL 723, except as indicated below. Exceptions: (1) Return-air and outside-air ducts, plenums, or concealed spaces that serve a dwelling unit shall be permitted to be of combustible construction. (2) Air filters meeting the requirements of Section 314.2 and Section 503.3. (3) Water evaporation media in an evaporative cooler. (4) Charcoal filters where protected with an approved fire suppression system. (5) Electrical wiring in plenums shall comply with NFPA 70. Electrical wires and cables and optical fiber cables shall be listed and labeled for use in plenums and shall have a flame spread distance not greater exceeding 5 feet (1524 mm), an average optical density not greater than exceeding 0.15, and a peak optical density not greater than exceeding 0.5, where tested in accordance with NFPA 262. (6) Nonmetallic fire sprinkler piping in plenums shall be listed and labeled for use in plenums and shall have a flame spread distance not greater than exceeding 5 feet (1524 mm), an average optical density not greater than exceeding 0.15 and, a peak optical density not greater than exceeding 0.5, when where tested in accordance with UL 1887. (7) Nonmetallic pneumatic tubing in plenums shall be listed and labeled for use in plenums and shall have a flame spread distance not greater than exceeding 5 feet (1524 mm), an average optical density not greater than exceeding 0.15, and a peak optical density not greater than exceeding 0.5, when where tested in accordance with UL 1820. (8) Loudspeakers and recessed lighting fixtures, including their assemblies and accessories, in plenums shall be listed and labeled for use in plenums and shall have a peak rate of heat release not greater than exceeding 134 horsepower (hp) (100 kw), an average optical density not greater than exceeding 0.15, and a peak optical density not greater than exceeding 0.5, when where tested in accordance with UL 2043. (9) Smoke detectors. (10) Duct insulation, coverings, and linings and other supplementary materials complying with Section 6054.0. (11) Materials in a Group H, Division 6, fabrication area including the areas above and below the fabrication area sharing a common air recirculation path with the fabrication area. 602.3 Factory-Made Air Ducts. Factory-made air ducts shall be approved for the use intended or shall be in accordance with the requirements of the referenced standard for air ducts in Chapter 17. Each portion of a factory-made air duct system UNIFORM MECHANICAL CODE 71

shall be identified by the manufacturer with a label or other identification indicating compliance with the referenced standard for air ducts in Chapter 17 and its class designation. These ducts shall be listed and shall be installed in accordance with the terms of their listing. 602.4 Joints and Seams of Ducts. Joints of duct systems shall be made substantially air-tight by means of tapes, mastics, gasketing, or other means. Crimp joints for round ducts shall have a contact lap of not less than 1½ inches (38 mm) and shall be mechanically fastened by means of not less than three sheet-metal screws equally spaced around the joint, or an equivalent fastening method. Joints and seams for 0.016 of an inch (0.41 mm) (No. 28 gauge) and 0.013 of an inch (0.33 mm) (No. 30 gauge) residential rectangular ducts shall be in accordance comply with Table 602.1(a) or SMACNA HVAC Duct Construction Standards - Metal and Flexible for 0.019 of an inch (0.48 mm) (No. 26 gauge) material. Joints and seams for rectangular duct systems shall be in accordance comply with Table 602.1(a) or SMACNA HVAC Duct Construction Standards - Metal and Flexible. Joints and seams for flat oval ducts and round ducts in other than single-dwelling units shall be in accordance comply with Table 602.1(f) or SMACNA HVAC Duct Construction Standards - Metal and Flexible. Joints and seams and all reinforcements for factory-made air ducts and plenums shall meet comply with the conditions of prior approval in accordance with the installation instructions that shall accompany the product. Closure systems for rigid air ducts and plenums shall be listed in accordance with UL 181A. Closure systems for flexible air ducts shall be listed in accordance with UL 181B. 602.5 Metal. Every dducts, plenums, or fittings of metal shall be in accordance comply with Table 602.1(a), Table 602.1(f), or SMACNA HVAC Duct Construction Standards - Metal and Flexible or duct systems in accordance with UL 181. Exception: Ducts, plenums, and fittings for systems serving single-dwelling units shall be permitted to be in accordance with Table 602.1(g). 602.6 Tin. Existing tin ducts may shall be permitted to be used when where cooling coils are added to a heating system, provided the first 10 feet (3048 mm) of the duct or plenum measured from the cooling coil discharge are constructed of metal of the gauge thickness set forth in accordance with Table 602.1(a), Table 602.1(f), Table 602.1(g) or SMACNA HVAC Duct Construction Standards - Metal and Flexible, other approved duct construction standard or are of approved material and construction. Tin ducts completely enclosed in inaccessible concealed areas need not be replaced. All aaccessible ducts shall be insulated to comply in accordance with Table 602.6(a), Table 602.6(b), or SMACNA HVAC Duct Construction Standards - Metal and Flexible. For the purpose of this subsection, ducts shall be considered accessible where the access space is 30 inches (762 mm) or greater in height. 602.7 Vibration Isolators. Vibration isolators installed between mechanical equipment and metal ducts (or casings) shall be made of an approved material and shall not exceed 10 inches (254 mm) in length. 603.0 Quality of Material. Galvanized steel shall be of lock-forming quality with a minimum coating of 1.25 ounces of zinc per square foot (0.04 kg/m 3 ) conforming to the requirements of. 6043.0 Installation of Ducts. 6043.1 General Ducts Under Floor or Crawl Space. Air ducts installed under a floor in a crawl space shall be installed as follows: (1) Shall not prevent access to any an area of the crawl space. (2) Where it is required to move under ducts for access to areas of the crawl space with a vertical clearance of not less than 18 inches (457 mm) shall be provided. 6043.2 Metal Ducts. Ducts shall be securely fastened in place at each change of direction in accordance with Table 604.2, or SMACNA HVAC Duct Construction Standards - Metal and Flexible. Vertical rectangular ducts and vertical round ducts shall be supported in accordance with Part A of Table 604.2, or SMACNA HVAC Duct Construction Standards - Metal and Flexible. Riser ducts shall be held in place by means of metal straps or angles and channels to secure the riser to the structure. Metal ducts shall be installed with not less than 4 inches (102 mm) separation from earth. Metal ducts when where installed in or under a concrete slab shall be encased in not less than 2 inches (51 mm) of concrete. Ducts shall be installed in a building with clearances to permit that will retain retaining the full thickness of fireproofing on structural members. Supports for rectangular ducts shall be in accordance comply with Table 604.2, or SMACNA HVAC Duct Construction Standards - Metal and Flexible, when where suspended from above, shall be installed on two opposite sides of each duct and shall be riveted, bolted, or metal screwed to each side of the duct at intervals specified. 6043.2.1 Horizontal Round Ducts. Horizontal round ducts not more than 40 inches (1016 mm) or less in diameter when where suspended from above shall be supported in accordance with Table 604.2 or SMACNA HVAC Duct Construction Standards - Metal and Flexible with one hanger per interval, installed, in accordance with Section 603.2.2 through Section 603.2.5. 6043.2.2 Tight-Fitting Around the Perimeter. Ducts shall be equipped with tight-fitting circular bands extending around the entire perimeter of the duct at each specified support interval. 6043.2.3 Size of Circular Bands. Circular bands shall be not less than 1 inch (25.4 mm) wide nor less than equivalent to the gauge of the duct material it supports. 72 UNIFORM MECHANICAL CODE

Exception: Ducts not more than 10 inches (254 mm) and less in diameter shall be permitted to be supported by No. 18 gauge galvanized steel wire. 6043.2.4 Connection. Each circular band shall be provided with means of connecting to the suspending support. 6043.2.5 Lateral Load. Ducts shall be braced and guyed to prevent lateral or horizontal swing. 6043.3 Factory-Made Air Ducts. Listed Class 0 or Class 1 factory-made air ducts shall be permitted to be installed in any an occupancy covered by this code. Factory-made air ducts shall not be used for vertical risers in air-duct systems serving more than two stories. Such ducts shall not penetrate construction where fire dampers are required. Factory-made air ducts shall be installed with not less than 4 inches (102 mm) of separation from earth, except where installed as a liner inside of concrete, tile, or metal pipe; they shall be protected from physical damage. TABLE 604.2 DUCT SUPPORT The temperature of the air to be conveyed in any of these classes of a ducts shall not exceed 250ºF (1221ºC). 6043.4 Protection of Ducts. Ducts installed in locations where they are exposed to mechanical damage by vehicles or from other causes shall be protected by approved barriers. 6043.5 Support of Ducts. Installers shall provide the manufacturer s field fabrication and installation instructions. In the absence of specific supporting materials and spacing, approved factory-made air ducts shall be permitted to be installed in accordance with Table 602.1(h), or SMACNA HVAC Duct Construction Standards - Metal and Flexible. 6043.6 Protection Against Flood Damage. In flood hazard areas, ducts shall be located above the elevation required by the building code for utilities and attendant equipment or the elevation of the lowest floor, whichever is higher, or shall be designed and constructed to prevent water from entering or accumulating within the ducts during floods up to A. VERTICAL DUCTS MAxIMUM SIDE OF RECTAN- METAL STRAP OR ANGLE MAxIMUM DIAMETER OF STRAP GULAR DUCT BRACKET ROUND DUCTS 24 1 x 1 8 strap 1 10 0.047 (No. 18 gauge) galvanized steel 36 1 x 1 x 1 8 angle 1 20 wide 1 0.058 (No. 16 gauge) galvanized steel 48 1 1 8 x 1 1 8 x 1 8 angle 1 40 1 8 steel x 1 1 2 1 60 1 1 2 x 1 1 2 x 1 8 angle 1 60 1 8 steel x 2 1 Over 60 2 x 2 x 1 8 angle 1 Over 60 3 16 steel x 2 1 B. HORIzONTAL DUCTS 18 1 x 18 gauge 2 10 30 1 x 18 gauge 2 48 1 x 1 8 2 20 60 1 x 1 8 2 40 80 1 x 1 8 2 60 Over 60 C. HORIzONTAL DUCTS TRAPEzE-TYPE SUPPORTS MAxIMUM DIAMETER OF ROUND DUCT OR SIDE OF RECTANGULAR DUCT HORIzONTAL SUPPORT ANGLE 3 36 1 1 2 x 1 1 2 x 1 8 48 2 x 2 x 1 8 60 2 x 2 x 1 8 84 2 x 2 x 1 8 For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm 1 Spaced vertically not more than 12 feet (3658 mm) on centers. 2 Spaced horizontally not more than 10 feet (3048 mm) on centers. 3 Spaced not more than 8 feet (2438 mm) on centers. Same gauge as galvanized steel duct, 1 inch wide or (No. 18 gauge galvanized steel wire) on 10 feet centers Same gauge as galvanized steel duct, 1 inch wide or (No. 8 gauge galvanized steel wire) tied to 1 inch galvanized steel band around duct on 10 feet centers Same gauge as galvanized steel duct, 1 1 2 inch wide on 6 feet centers Same gauge as galvanized steel duct, 1 1 2 inch wide on 4 feet centers HANGER 1 4 round rod or 1 x 1 x 1 8 angle 1 4 round rod or 1 x 1 x 1 8 angle 5 16 round rod or 1 x 1 x 1 8 angle 3 8" round rod or 1" x 1" x 1 8" angle UNIFORM MECHANICAL CODE 73

such elevation. Where the ducts are located below that elevation, the ducts shall be capable of resisting hydrostatic and hydrodynamic loads and stresses, including the effects of buoyancy, during the occurrence of flooding to such elevation. 6054.0 Insulation of Ducts. 6054.1 General. Supply-air ducts, return-air ducts, and plenums of a heating or cooling system shall be insulated to achieve the minimum thermal (R) value as set forth in accordance with Table 602.6(a), Table 602.6(b), or SMACNA HVAC Duct Construction Standards - Metal and Flexible. Exceptions: (1) Factory-installed plenums, casings, or ductwork furnished as a part of HVAC equipment tested and rated in accordance with approved energy efficiency standards. (2) Ducts or plenums located in conditioned spaces where heat gain or heat loss will not increase energy use. (3) For runouts less than 10 feet (3048 mm) in length to air terminals or air outlets, the rated R value of insulation need not exceed R-3.5 (R-0.6). (4) Backs of air outlets and outlet plenums exposed to unconditioned or indirectly conditioned spaces with face areas exceeding 5 square feet (0.5 m 2 ) need not exceed R-2 (R-0.4); those 5 square feet (0.5 m 2 ) or smaller need not be insulated. (5) Ducts and plenums used exclusively for evaporative cooling systems. Approved materials shall be installed within ducts and plenums for insulating, sound deadening, or other purposes. Materials shall have a mold, humidity, and erosion-resistant surface that meets the requirements of the referenced standard for air ducts in Chapter 17. Duct liners in systems operating with air velocities exceeding 2000 feet per minute (10.2 m/s) shall be fastened with both adhesive and mechanical fasteners, and exposed edges shall have adequate approved treatment to withstand the operating velocity. Insulation applied to the surface of ducts, including duct coverings, linings, tapes, and adhesives, located in buildings shall have a flame-spread index not greater than to exceed 25 and a smoke developed index not greater than to exceed 50, where tested in accordance with NFPA 255, or in accordance with ASTM E 84, or in accordance with the provisions of UL 723. The specimen preparation and mounting procedures of ASTM E 2231 shall be used. Air duct coverings and linings shall not flame, glow, smolder, or smoke when where tested in accordance with ASTM C 411 at the temperature to which they are exposed in service. In no case shall the test temperature be less than 250ºF (121ºC). Factory-made air ducts and faced insulations intended for installation on the exterior of ducts shall be legibly printed with the name of the manufacturer, the thermal resistance (R) value at installed thickness, and the flame-spread index and smoke developed index of the composite material. 6065.0 Smoke Dampers, Fire Dampers, and Ceiling Dampers. 6065.1 Smoke Dampers. Smoke dampers shall comply with the standards for leakage-rated dampers referenced in Chapter 17, and shall be installed in accordance with the approved manufacturer s installation instructions where required by the building code. Smoke dampers shall be labeled by an approved agency. 6065.2 Fire Dampers. Fire dampers shall comply with the standard for fire dampers referenced in Chapter 17, and shall be installed in accordance with the approved manufacturer s installation instructions where required by the building code. Fire dampers shall have been tested for closure under airflow conditions and shall be labeled for both maximum airflow permitted and direction of flow. Where more than one damper is installed at a point in a single air path, the entire airflow shall be assumed to be passing through the smallest damper area. Fire dampers shall be labeled by an approved agency. Ductwork shall be connected to damper sleeves or assemblies in accordance with the fire damper manufacturer s installation instructions. 6065.3 Ceiling Radiation Dampers. Ceiling radiation dampers shall comply with the standard for ceiling radiation dampers referenced in Chapter 17, and shall be installed in accordance with the manufacturer s approved installation instructions in the fire-resistive ceiling element of floor-ceiling and roof-ceiling assemblies where required by the building code. Fire dampers not meeting the temperature limitation of ceiling radiation dampers shall not be used as a substitute. Ceiling radiation dampers shall be labeled by an approved agency. 6065.4 Multiple Arrangements. Where size requires the use of multiple dampers, the installation shall be framed in an approved manner to ensure that the dampers remain in place. 6065.5 Access and Identification. Dampers shall be provided with an approved means of access large enough to permit inspection and maintenance of the damper and its operating parts. The access shall not impair fire-resistive construction. Access shall not require the use of tools, keys, or special knowledge. Access points shall be permanently identified on the exterior by a label with letters not less than 1 2 of an inch (12.7 mm) in height reading: SMOKE DAMPER or FIRE DAMPER. Access doors in ducts shall be tight fitting and approved for the required duct construction. 6065.6 Freedom from Interference. Dampers shall be installed in a manner to ensure positive closing or opening as required by function. Interior liners or insulation shall be held back from portions of a damper, its sleeve, or adjoining duct that would interfere with the damper s proper operation. Exterior materials shall be installed so as to not interfere with the operation or maintenance of external operating devices needed for the function of the damper. 6065.7 Temperature Classification of Operating Elements. Fusible links, thermal sensors, and pneumatic or electric operators shall have a temperature rating or classification as required by in accordance with the building code. 74 UNIFORM MECHANICAL CODE

6076.0 Ventilating Ceilings. 6076.1 General. Perforated ceilings shall be permitted to be used for air supply within the limitations of this section. Exit corridors, where required to be of fire-resistive construction by the building code, shall not have ventilating ceilings. 6076.2 Requirements. Ventilating ceilings shall be in accordance comply with the following provisions:. (1) Suspended ventilating ceiling material shall have a Class I flame-spread classification on both sides, determined in accordance with the Building Code. Suspended ventilating ceiling supports shall be of noncombustible materials. (2) Lighting fixtures recessed into ventilating ceilings shall be of a type approved for that purpose. 6087.0 Use of Under-Floor Space as Supply Plenum for Dwelling Units. 607.1 General. An under-floor space may shall be permitted to be used as a supply plenum, provided:. 6087.12 Dwelling Units. The use of under-floor space shall be limited to dwelling units not more than two stories in height. Except for the floor immediately above the underfloor plenum, supply ducts shall be provided extending from the plenum to registers on other floor levels. Exception: In flood hazard areas, under-floor spaces shall not be used as supply plenums unless the flood opening requirements in the building code are met. 6087.23 Enclosed. Such spaces shall be cleaned of all loose combustible scrap material and shall be tightly enclosed. 6087.34 Flammable Materials. The enclosing material of the under-floor space, including the sidewall insulation, shall be not more flammable than 1 inch (25 mm) (nominal) wood boards (flame-spread index of 200). Installation of foam plastics is regulated by the building code. 6087.45 Access. Access shall be through an opening in the floor and shall be not less than 24 inches by 24 inches (610 mm x by 610 mm). 6087.56 Automatic Control. A furnace supplying warm air to under-floor space shall be equipped with an automatic control that will start the air-circulating fan where the air in the furnace bonnet reaches a temperature not higher than exceeding 150ºF (66ºC). Such control shall be one that cannot be set higher than to exceed 150ºF (66ºC). 6087.67 Temperature Limit. A furnace supplying warm air to such space shall be equipped with an approved temperature limit control that will limit outlet air temperature to 200ºF (93ºC). 6087.78 Noncombustible Receptacle. A noncombustible receptacle shall be placed below each floor opening into the air chamber, and such receptacle shall comply with to the following sections. 6087.78.1 Location. The receptacle shall be securely suspended from the floor members and shall be not more than 18 inches (457 mm) below the floor opening. 6087.78.2 Area. The area of the receptacle shall extend 3 inches (76 mm) beyond the opening on all sides. 6087.78.3 Perimeter. The perimeter of the receptacle shall have a vertical lip not less than 1 inch (25.4 mm) high at the open sides where it is at the level of the bottom of the joists, or 3 inches (76 mm) high if where the receptacle is suspended. 6087.89 Floor Registers. Floor registers shall be designed for easy removal in order to give access for cleaning the receptacles. 6087.910 Exterior Wall and Interior Stud Partitions. Exterior walls and interior stud partitions shall be fire-stopped at the floor. 6087.101 Wall Register. Each wall register shall be connected to the air chamber by a register box or boot. 6087.112 Distance from Combustible. A duct conforming complying with Section 602.0 shall extend from the furnace supply outlet not less than 6 inches (152 mm) below combustible framing. 6087.123 Vapor Barrier. The entire ground surface of the under-floor space shall be covered with a vapor barrier having a minimum thickness of not less than 4 mils (0.1 mm) and a flame-spread index of not more than 200 or less. 6087.134 Prohibition. Fuel-gas lines and plumbing waste cleanouts are not located within the space. 6098.0 Automatic Shutoffs. 608.1 General. Air-moving systems supplying air in excess of 2000 cubic feet per minute (ft 3 /min) (944 L/s 0.9439 m 3 /s) to enclosed spaces within buildings shall be equipped with an automatic shutoff. Automatic shutoff shall be accomplished by interrupting the power source of the air-moving equipment upon detection of smoke in the main supply-air duct served by such equipment. Smoke detectors shall be labeled by an approved agency for air duct installation and shall be installed in accordance with the manufacturer s approved installation instructions. Such devices shall be compatible with the operating velocities, pressures, temperatures, and humidities of the system. Where fire-detection or alarm systems are provided for the building, the smoke detectors required by this section shall be supervised by such systems. Exceptions: (1) Where the space supplied by the air-moving equipment is served by a total coverage smoke-detection system in accordance with the fire code, interconnection to such system shall be permitted to be used to accomplish the required shutoff. (2) Automatic shutoff is not required where all occupied rooms served by the air-handling equipment have direct exit to the exterior and the travel distance does not exceed 100 feet (30 480 mm). (3) Automatic shutoff is not required for Group R, Division 3 and Group U Occupancies. (4) Automatic shutoff is not required for approved smokecontrol systems or where analysis demonstrates shutoff UNIFORM MECHANICAL CODE 75

would create a greater hazard, such as shall be permitted to be encountered in air-moving equipment supplying specialized portions of Group H Occupancies. Such equipment shall be required to have smoke detection with remote indication and manual shutoff capability at an approved location. (5) Smoke detectors that are factory installed in listed airmoving equipment shall be permitted to be used in lieu of smoke detectors installed in the main supply-air duct served by such equipment. 76 UNIFORM MECHANICAL CODE

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78 UNIFORM MECHANICAL CODE

Galvanized Steel (Gauge) nominal Minimum Aluminum. equivalent* inches TABLE 602.1(c) THICKNESS ADJUSTMENTS RECTANGULAR ALUMINUM DUCT ADAPTED FROM 3 INCH WATER COLUMN (750 Pa) OR LOWER 28 26 24 22 20 18 16 0.023 0.027 0.034 0.043 0.052 0.067 0.083 Commercial size inches 0.025 0.032 0.04 0.05 0.063 0.071 0.09 Pounds of weight/square feet aluminum For SI units: 1 inch = 25.4 mm * Alloy 3003-H-14. * Calculate an effective Ix= 3x that used for steel. TABLE 602.1(d) DIMENSION ADJUSTMENTS Consult Appendix-5 for Weights RECTANGULAR ALUMINUM DUCT ADAPTED FROM 3 INCH WATER COLUMN (750 Pa) OR LOWER Galv. Rigidity Class A B C D E F G H I J K L Alum. dim. per Galv. Class C E E F H I I K 1* 1* 1* 1* STEEL ANGLE SIzE, 1 x 1 x 16 Ga. 1 x 1 x 1 8 1 1 4 x 1 1 4 x 1 8 RECTANGULAR ALUMINUM DUCT ADAPTED FROM 3 INCH WATER COLUMN (750 Pa) OR LOWER COD C D F TABLE 602.1(e) REINFORCEMENTS EQUIVALENT ALUMN, * ANGLE SIzE, STEEL BAR ALUMINUM BAR 1 1 1 4 x 1 1 4 x 1 8 1 x 1 8 1 1 2 x 1 8 or 1 1 4 x 3 16 1 1 2 x 1 1 2 x 1 8 1 1 2 x 1 8 1 1 2 x 1 8 x or 1 1 4 x 3 16 1 3 4 x 1 3 4 x 1 8 1 1 2 x 1 1 2 x 1 8 G 2 1 2 x 2 1 2 x 1 8 2 x 2 x 1 8 H 2 1 2 x 2 1 2 x 3 16 2 x 2 x 3 16 I 2 1 2 x 2 1 2 x 3 8 or 3 x 3 x 1 4 2 x 2 x 1 4 J 2 1 2 x 2 1 2 x 3 8 or 3 x 3 x 1 4 2 1 2 x 2 1 2 x 3 16 K 3 x 3 x 3 8 or 3 1 2 x 3 1 2 x 1 4 For SI units: 1 inch = 25.4 mm * Alloy 6061-T6 Strength normally. Any aluminum shape substitute shall have a moment of inertia three times that of steel and have 30 000 psi minimum yield strength. UNIFORM MECHANICAL CODE 79

DUCT DIAMETER MAx. WIDTH ( inches) Aluminum B. & S. Gage PRESSURE < 2 INCH WATER COLUMN Up to 9 24 Over 9 Up to 14 Over 14 Up to 23 Over 23 Up to 37 Over 37 Up to 51 Over 51 Up to 61 Over 61 Up to 84 TABLE 602.1(f) CONSTRUCTION DETAILS FOR ROUND AND FLAT-OVAL DUCTS STEEL THICKNESS IN INCHES (STEEL GALVANIzED SHEET GAUGE) PRESSURE < 2 INCH WATER COLUMN 2 ROUND ROUND FLAT- OVAL 24 22 20 18 16 14 0.019 (26) 0.019 (26) 0.024 (24) 0.030 (22) 0.047 (18) 0.058 (16) 0.024 (24) 0.024 (24) 0.030 (22) 0.047 (18) PRESSURE > 2 < 10 INCH WATER SPIRAL SEAM 0.019 (26) 0.024 (24) 0.024 (24) 0.030 (22) 0.058 X 0.070 X COLUMN LONGITUDINAL SEAM 0.024 (24) 0.030 (22) 0.047 (18) 0.058 (16) WELDED FITTINGS 0.030 (22) 0.047 (18) 0.047 (18) 0.058 (16) PRESSURE > 2 < 10 INCH WATER COLUMN GIRTH JOINTS 1 MINIMUM GIRTH REINFORCING, MAxIMUM SPACING AND ANGLE SIzE 2 Slip None 4 Slip None 4 Slip None 4 Slip None 1 1 4 x 1 1 4 x 1 8 Flange 1 1 4 x 1 1 4 x 1 8 on 72 1 1 2 x 1 1 2 x 1 8 Flange 1 1 4 x 1 1 4 x 1 8 on 72 1 1 4 x 1 1 4 x 1 8 1 1 2 x 1 1 2 x 1 8 on 48 For SI units: 1 inch = 25.4 mm, 1 inch water column = 0.249 kpa 1 For pressure <2 inches water column (50 kpa), any of the following joints are acceptable: butt slip; pipe slip; pipe lock; roll slip; snap slip; plenum lock; and companion flange. 2 Acceptable longitudinal seams for pressure < 2 inches water column (50 kpa): Acme (grooved); snap lock; standing; and spiral. TABLE 602.1(g) THICKNESS OF METAL DUCTS AND PLENUMS USED FOR HEATING OR COOLING FOR A SINGLE-DWELLING UNIT MINIMUM THICKNESS, INCHES GALVANIzED STEEL EQUIVALENT GALVANIzED SHEET GAUGE NO. APPROxIMATE ALUMINUM B. & S. Round ducts and enclosed rectangular ducts 14 or less 0.013 30 26 Over 14 0.016 28 24 Exposed rectangular ducts xx 14 or less 0.016 28 24 Over 14 0.019 26 22 For SI units: 1 inch = 25.4 mm CLASS 1 DUCT MATERIAL TABLE 602.1(h) ALTERNATE SUPPORTS FOR FACTORY-MADE AIR DUCTS MINIMUM SUPPORT MATERIAL MAxIMUM SUPPORT SPACING (feet) Rigid round fibrous No. 26 gauge x 5 8 wide galvanized iron strap 6 Corrugated metal No. 18 gauge galvanized iron wire 6 Flexible No. 26 gauge x 1 1 2 wide galvanized iron strap 4 For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm 80 UNIFORM MECHANICAL CODE

TABLE 602.6(a) (I-P UNITS) MINIMUM DUCT INSULATION R VALUE A COOLING AND HEATING ONLY SUPPLY DUCTS AND RETURN DUCTS 4, 5 CLIMATE zone DUCT LOCATION ENVELOPE CRITERIA TABLE HDD65 CDD50 ExTERIOR VENTILATED ATTIC UNVENTED ATTIC W/ ROOF INSULA- TION UNCONDI- TIONED SPACE 1 UNCONDI- TIONED SPACE 2 INDIRECTLY CONDI- TIONED SPACE 3 BURIED HEATING-ONLY DUCTS 5-1 to 5-7 0 1800 all none none none none none none none 5-8 to 5-12 1801 3600 all R-3.5 none none none none none none 5-13 to 5-15 3601 5400 all R-3.5 none none none none none none 5-16 to 5-18 5401 7200 all R-6 R-3.5 none none none none R-3.5 5-19 to 5-20 7201 9000 all R-6 R-6 R-3.5 none none none R-3.5 5-21 to 5-22 9001 10 800 all R-8 R-6 R-6 none R-3.5 none R-3.5 5-23 10 801 12 600 all R-8 R-6 R-6 none R-6 none R-6 5-24 12 601 16 200 all R-8 R-8 R-6 none R-6 none R-6 5-25 16 201 19 800 all R-10 R-8 R-8 none R-6 none R-6 5-26 19 801+ all R-10 R-10 R-8 none R-8 none R-6 COOLING-ONLY DUCTS 5-15, 18, 20, 22 to 26 all 0 1800 R-1.9 R-1.9 R-1.9 R-1.9 R-1.9 none none 5-12, 14, 17, 19, 21 all 1801 3600 R-3.5 R-1.9 R-3.5 R-1.9 R-1.9 none none 5-7, 9, 11, 13, 16 all 3601 5400 R-3.5 R-3.5 R-6 R-1.9 R-1.9 none none 5-4, 6, 8, 10 all 5401 7200 R-6 R-6 R-6 R-3.5 R-1.9 none none 5-3, 5-5 all 7201 9000 R-6 R-6 R-6 R-3.5 R-3.5 none R-3.5 5-2 all 9001 10 800 R-6 R-6 R-8 R-3.5 R-3.5 none R-3.5 5-1 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 1 Insulation R-values, measured in (h ft 2 ºF)/Btu, 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 exterior walls are used as plenum walls, wall insulation shall be as required by the most restrictive condition. Insulation resistance measured on a horizontal plane in accordance with ASTM C518 at a mean temperature of 75ºF (24ºC) at the installed thickness. 2 Includes crawl spaces, both ventilated and nonventilated. 3 Includes return-air plenums with or without exposed roofs above. 4 Vapor retarders shall be installed on supply ducts in spaces vented to the outside in geographic areas where the average summer dewpoint temperature based on the 2 1 2 percent column of dry-bulb and mean coincident wet-bulb temperature exceeds 60ºF (16ºC). 5 Insulation shall have an approved weatherproof barrier. UNIFORM MECHANICAL CODE 81

TABLE 602.6(b) (I-P UNITS) MINIMUM DUCT INSULATION R VALUE A COMBINED HEATING AND COOLING DUCTS 4, 5 CLIMATE zone DUCT LOCATION ENVELOPE CRITERIA TABLE HDD65 CDD50 ExTERIOR VENTILATED ATTIC UNVENTED ATTIC W/ ROOF INSULA- TION UNCONDI- TIONED SPACE 1 UNCONDI- TIONED SPACE 2 INDIRECTLY CONDI- TIONED SPACE 3 BURIED 5-1 0 900 10 801+ R-8 R-6 R-8 R-3.5 R-3.5 none R-3.5 5-2 0 900 9001 10 800 R-6 R-6 R-8 R-3.5 R-3.5 none R-3.5 5-3 0 900 7201 9000 R-6 R-6 R-6 R-3.5 R-3.5 none R-3.5 5-4 0 900 0 7200 R-6 R-3.5 R-6 R-3.5 R-1.9 none R-3.5 5-5 901 1800 7201+ R-6 R-6 R-6 R-3.5 R-3.5 none R-3.5 5-6 901 1800 5401 7200 R-6 R-6 R-6 R-3.5 R-3.5 none R-3.5 5-7 901 1800 0 5400 R-3.5 R-3.5 R-6 R-1.9 R-1.9 none R-1.9 5-8 1801 2700 5401+ R-6 R-6 R-6 R-3.5 R-3.5 none R-3.5 5-9 1801 2700 0 5400 R-6 R-3.5 R-6 R-1.9 R-1.9 none R-1.9 5-10 2701 3600 5401+ R-6 R-6 R-6 R-3.5 R-3.5 none R-3.5 5-11 2701 3600 3601 5400 R-6 R-6 R-6 R-3.5 R-3.5 none R-1.9 5-12 2701 3600 0 3600 R-3.5 R-3.5 R-3.5 R-1.9 R-1.9 none R-1.9 5-13 3601 5400 3601+ R-6 R-6 R-6 R-3.5 R-3.5 none R-3.5 5-14 3601 5400 1801 3600 R-6 R-3.5 R-6 R-1.9 R-3.5 none R-1.9 5-15 3601 5400 0-1800 R-3.5 R-3.5 R-3.5 R-1.9 R-1.9 none R-1.9 5-16 5401 7200 3601+ R-6 R-6 R-6 R-3.5 R-3.5 none R-3.5 5-17 5401 7200 1801 3600 R-6 R-6 R-6 R-1.9 R-3.5 none R-3.5 5-18 5401 7200 0 1800 R-6 R-3.5 R-3.5 R-1.9 R-3.5 none R-3.5 5-19 7201 9000 1801+ R-8 R-6 R-6 R-1.9 R-3.5 none R-3.5 5-20 7201 9000 0 1800 R-6 R-6 R-6 R-1.9 R-3.5 none R-3.5 5-21 9001 10 800 1801+ R-8 R-6 R-6 R-1.9 R-6 none R-3.5 5-22 9001 10 800 0 1800 R-8 R-6 R-6 R-1.9 R-3.5 none R-3.5 5-23 10 801 12 600 all R-8 R-6 R-6 R-1.9 R-6 none R-6 5-24 12 601 16 200 all R-8 R-8 R-8 R-1.9 R-6 none R-6 5-25 16 201 19 800 all R-10 R-8 R-8 R-3.5 R-6 none R-6 5-26 19 801+ all R-10 R-10 R-8 R-3.5 R-8 R-3.5 R-6 1 Insulation R-values, measured in (h ft 2 F)/Btu, 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 exterior walls are used as plenum walls, wall insulation shall be as required by the most restrictive condition. Insulation resistance measured on a horizontal plane in accordance with ASTM C518 at a mean temperature of 75 F (24ºC) at the installed thickness. 2 Includes crawl spaces, both ventilated and nonventilated. 3 Includes return air plenums with or without exposed roofs above. 4 Vapor retarders shall be installed on cooling supply ducts in spaces vented to the outside in geographic areas where the average summer dewpoint temperature based on the 2 1 2 percent column of dry-bulb and mean coincident wet-bulb temperature exceeds 60 F (16 C). 5 Insulation shall have an approved weatherproof barrier. 82 UNIFORM MECHANICAL CODE