N.Y.C. Admin. Code § MC 603: Section MC 603: Duct Construction and Installation

603.1 General.

An air distribution system shall be designed and installed to supply the required distribution of air. The installation of an air distribution system shall not affect the fire protection requirements specified in the New York City Building Code. Ducts shall be constructed, braced, reinforced and installed to provide structural strength and durability.

603.2 Duct sizing.

Ducts installed within a single dwelling unit shall be sized in accordance with ACCA Manual D, the appliance manufacturer's instructions or other approved methods. Ducts installed within all other buildings shall be sized in accordance with the ASHRAE Handbook of Fundamentals or other equivalent computation procedure.

603.3 Duct classification.

Ducts shall be classified based on the maximum operating pressure of the duct at pressures of positive or negative 0.5, 1.0, 2.0, 3.0, 4.0, 6.0 or 10.0 inches (1 inch w.c. = 248.7 Pa) of water column. The pressure classification of ducts shall equal or exceed the design pressure of the air distribution in which the ducts are utilized.

603.4 Metallic ducts.

Metallic ducts shall be constructed as specified in the SMACNA/ANSI HVAC Duct Construction Standards – Metal and Flexible.

Exception: Ducts installed within single dwelling units shall have a minimum thickness as specified in Table 603.4.

Table 603.4 Duct Construction Minimum Sheet Metal Thickness for Single Dwelling Units

a

Round Duct Diameter (inches)

Static Pressure

1/2-inch water gage Thickness (inches)

1-inch water gage Thickness (inches)

Galvanized

Aluminum

Galvanized

Aluminum

< 12

0.013

0.018

0.013

0.018

12 to14

0.013

0.018

0.016

0.023

15 to 17

0.016

0.023

0.019

0.027

18

0.016

0.023

0.024

0.034

19 to 20

0.019

0.027

0.024

0.034

Rectangular Duct Dimension (inches)

Static Pressure

1/2-inch water gage Thickness (inches)

1-inch water gage Thickness (inches)

Galvanized

Aluminum

Galvanized

Aluminum

£ 8

0.013

0.018

0.013

0.018

9 to10

0.013

0.018

0.016

0.023

11 to 12

0.016

0.023

0.019

0.027

13 to16

0.019

0.027

0.019

0.027

17 to 18

0.019

0.027

0.024

0.034

19 to 20

0.024

0.034

0.024

0.034

For SI: 1 inch = 25.4 mm, 1-inch water gage = 249 Pa.

a. Ductwork that exceeds 20 inches by dimension or exceeds a pressure of 1-inch water gage shall be constructed in accordance with SMACNA/ANSI HVAC Duct Construction Standards – Metal and Flexible.

603.4.1 Minimum fasteners.

Round metallic ducts shall be mechanically fastened by means of not less than three sheet metal screws or rivets spaced equally around the joint.

Exception: Where a duct connection is made that is partially inaccessible, three screws or rivets shall be equally spaced on the exposed portion so as to prevent a hinge effect.

603.4.2 Duct lap.

Crimp joints for round and oval metal ducts shall be lapped not less than 1 inch (25.4 mm) and the male end of the duct shall extend into the adjoining duct in the direction of airflow.

603.5 Nonmetallic ducts.

Nonmetallic ducts shall be constructed with Class 0 or Class 1 duct material and shall comply with UL 181. Fibrous duct construction shall conform to the SMACNA/ANSI Fibrous Glass Duct Construction Standards or NAIMA Fibrous Glass Duct Construction Standards. The air temperature within nonmetallic ducts shall not exceed 250°F (121.1°C).

603.6 Air ducts and air connectors.

Air ducts, both metallic and nonmetallic, shall comply with Section 603.6.1. Air connectors, both metallic and nonmetallic, shall comply with Sections 603.6.2 and 603.6.3.

603.6.1 Air ducts.

Air ducts shall be permitted to be rigid or flexible and shall be constructed of materials that are reinforced and sealed to satisfy the requirements for the use of the air duct system, such as the supply air system, the return or exhaust air system, and the variable volume/pressure air system.

603.6.1.1 Materials.

All air duct materials shall be suitable for continuous exposure to the temperature and humidity conditions of the environmental air in the air duct. Air ducts shall be constructed of any of the following materials:

1. Iron, steel, aluminum, copper, concrete, masonry or clay tile.

2. Class 0 or Class 1 rigid or flexible air ducts tested in accordance with UL 181 and installed in conformance with the conditions of the listing.

Exceptions:

1. Class 0 or Class 1 rigid or flexible air duct shall not be used as a vertical air duct that is more than two stories in height.

2. Class 0 or Class 1 rigid or flexible air ducts shall not be used for air ducts containing air at temperatures in excess of 250°F (121.1°C).

3. Where the temperature of the conveyed air does not exceed 125°F (51.7°C) in normal service, negative pressure exhaust or return air ducts shall be permitted to be constructed of gypsum board having a maximum flame spread index/rating of 25 without evidence of continued progressive combustion and a maximum smoke-developed index/rating of 50. Air ducts formed by gypsum boards shall have a surface temperature maintained above the airstream dew-point temperature, and shall not be used in air-handling systems utilizing evaporative coolers.

Exception: The maximum conveyed air temperature of 125°F (52°C) shall not apply to gypsum board material used for post-fire smoke purge.

603.6.1.2 Installation.

The materials, thickness, construction, and installation of ducts shall provide structural strength and durability in conformance with recognized good practice. Air ducts shall be considered to be in compliance with this requirement where constructed and installed in accordance with the New York City Building Code. Where no standard exists for the construction of air ducts, they shall be constructed to withstand both the positive and negative pressures of the system.

603.6.2 Air connectors.

Air connectors are limited-use, flexible air ducts that are required to conform to other provisions applicable to air ducts and shall meet the following requirements:

1. Air connectors shall conform to the requirements for Class 0 or Class 1 connectors when tested and approved in accordance with UL 181.

2. Class 0 or Class 1 air connectors shall not be used for ducts containing air at temperatures in excess of 250°F (121.1°C).

3. Air connector runs shall not exceed 14 feet (4267.2 mm) in length.

4. Air connectors shall not penetrate any rated wall, partition, or shaft that is required to have a fire-resistance rating of 1 hour or more.

5. Air connectors shall not pass through floors.

603.6.3 Flexible air duct and air connector clearance.

Flexible air ducts and air connectors shall be installed with a minimum clearance to an appliance as specified in the appliance manufacturer's instructions.

603.7 Rigid duct penetrations.

Duct system penetrations of walls, floors, ceilings and roofs and air transfer openings in such building components shall be protected as required by Section 607. Ducts in a private garage that penetrate a wall or ceiling that separates a dwelling from a private garage shall be continuous, shall be constructed of sheet steel having a thickness of not less than 0.0187 inch (0.4712 mm) (No. 26 gage) and shall not have openings into the garage. Fire and smoke dampers are not required in such ducts passing through the wall or ceiling separating a dwelling from a private garage except where required by Chapter 7 of the New York City Building Code.

603.8 Underground ducts.

Ducts shall be approved for underground installation. Metallic ducts not having an approved protective coating shall be completely encased in not less than 2 inches (50.8 mm) of concrete.

603.8.1 Slope.

Ducts shall have a minimum slope of 1/8 inch per foot (10.4 mm/m) to allow drainage to a point provided with access.

603.8.2 Sealing.

Ducts shall be sealed and secured prior to pouring the concrete encasement.

603.8.3 Plastic ducts and fittings.

Plastic ducts shall be constructed of PVC having a minimum pipe stiffness of 8 psi (55.1 kPa) at 5-percent deflection when tested in accordance with ASTM D 2412. Plastic duct fittings shall be constructed of either PVC or high-density polyethylene. Plastic duct and fittings shall be utilized in underground installations only. The maximum design temperature for systems utilizing plastic duct and fittings shall be 150°F (65.6°C).

603.9 Joints, seams and connections.

All longitudinal and transverse joints, seams and connections in metallic and nonmetallic ducts shall be constructed as specified in SMACNA/ANSI HVAC Duct Construction Standards – Metal and Flexible and NAIMA Fibrous Glass Duct Construction Standards. All joints, longitudinal and transverse seams and connections in ductwork shall be securely fastened and sealed with welds, gaskets, mastics (adhesives), mastic-plus-embedded-fabric systems, liquid sealants or tapes. Tapes and mastics used to seal fibrous glass ductwork shall be listed and labeled in accordance with UL 181A and shall be marked "181 A-P" for pressure-sensitive tape, "181 A-M" for mastic or "181 A-H" for heat-sensitive tape. Tapes and mastics used to seal metallic and flexible air ducts and flexible air connectors shall comply with UL 181B and shall be marked "181 B-FX" for pressure-sensitive tape or "181 B-M" for mastic. Duct connections to flanges of air distribution system equipment shall be sealed and mechanically fastened. Mechanical fasteners for use with flexible nonmetallic air ducts shall comply with UL 181B and shall be marked "181 B-C." Closure systems used to seal all ductwork shall be installed in accordance with the manufacturer's instructions.

Exception: For ducts having a static pressure classification of less than 2 inch w.c. (497.7 Pa), additional closure systems shall not be required for continuously welded joints and seams and locking-type joints and seams of other than the snap-lock and buttonlock types.

603.10 Supports.

Ducts shall be supported in accordance with SMACNA/ANSI HVAC Duct Construction Standards – Metal and Flexible. Flexible and other factory-made ducts shall be supported in accordance with the manufacturer's instructions. Ducts shall not be hung from or supported by suspended ceilings.

603.11 Furnace connections.

Ducts connecting to a furnace shall have a clearance to combustibles in accordance with the furnace manufacturer's instructions.

603.11.1 Air duct at heat sources.

Where heat sources from electrical equipment, fossil fuel-burning equipment, or solar energy collection equipment are installed in air ducts, the installation shall avoid the creation of a fire hazard. Air ducts rated as Class 1 in accordance with UL 181, air duct coverings, and linings shall be interrupted at the immediate area of operation of such heat sources in order to meet the clearances specified in the equipment listing.

Exceptions:

1. Appliances listed for zero clearance from combustibles where installed with the conditions of their listings.

2. Insulation specifically suitable for the maximum temperature that reasonably can be anticipated on the duct surface shall be permitted to be installed at the immediate area of operation of such appliances.

603.12 Condensation.

Provisions shall be made to prevent the formation of condensation on the exterior of any duct.

603.13 Flood hazard areas.

For structures in flood hazard areas, ducts shall comply with the additional requirements of Appendix G of the New York City Building Code.

603.14 Location.

Ducts shall not be installed in or within 4 inches (101.6 mm) of the earth, except where such ducts comply with Section 603.8.

603.15 Mechanical protection.

Ducts installed in locations where they are exposed to mechanical damage by vehicles or from other causes shall be protected by approved vehicle barriers as required by the New York City Building Code.

603.16 Weather protection.

Ducts including linings, coverings and vibration isolation connectors installed on the exterior of the building shall be protected against the elements.

603.17 Air dispersion systems.

Air dispersion systems shall:

1. Be installed entirely in exposed locations or in underfloor air supply plenums.

2. Be utilized in systems under positive pressure.

3. Not pass through or penetrate fire-resistant-rated construction.

4. Be listed and labeled in compliance with UL 2518.

603.18 Registers, grilles and diffusers.

Duct registers, grilles and diffusers shall be installed in accordance with the manufacturer's instructions and securely fastened to the ductwork. Volume dampers or other means of supply air adjustment shall be provided in the branch ducts or at each individual duct register, grille or diffuser. Each volume damper or other means of supply air adjustment used in balancing shall be provided with access.

603.18.1 Floor registers.

Floor registers shall resist, without structural failure, a 200-pound (90.8 kg) concentrated load on a 2-inch-diameter (50.8 mm) disc applied to the most critical area of the exposed face.

603.18.2 Prohibited locations.

Diffusers, registers and grilles shall be prohibited in the floor or its upward extension within toilet and bathing rooms required by the New York City Building Code to have smooth, hard, nonabsorbent surfaces.

Exception: In R-3 occupancies.

603.19 Vibration isolation connectors.

Vibration isolation connectors in duct systems shall be made of an approved flame-retardant fabric or shall consist of sleeve joints with packing of approved material, each having a maximum flame spread index/rating of 25 and a maximum smoke-developed rating of 50. The fabric shall have a maximum length of 10 inches (254 mm) in the direction of airflow.