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 International Building Code. Ducts shall be constructed, braced, reinforced and installed to provide structural strength and durability.
Ducts installed within a single dwelling unit shall be sized in accordance with ACCA Manual D, the appliance manufacturer's installation 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.
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.
Metallic ducts shall be constructed as specified in the SMACNA HVAC Duct Construction Standards‒Metal and Flexible.
TABLE 603.4 DUCT CONSTRUCTION MINIMUM SHEET METAL THICKNESS FOR SINGLE DWELLING UNITSa
For SI: 1 inch = 25.4 mm, 1-inch water gage = 249 Pa.
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 UNITSa
| ROUND DUCT DIAMETER (inches) |
STATIC PRESSURE | |||
| 1/2-inch water gage | 1-inch water gage | |||
| Thickness (inches) | 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 | 1-inch water gage | |||
| Thickness (inches) | Thickness (inches) | |||
| Galvanized | Aluminum | Galvanized | Aluminum | |
| 8 | 0.013 | 0.018 | 0.013 | 0.018 |
| 9 to 10 | 0.013 | 0.018 | 0.016 | 0.023 |
| 11 to 12 | 0.016 | 0.023 | 0.019 | 0.027 |
| 13 to 16 | 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.
- Ductwork that exceeds 20 inches by dimension or exceeds a pressure of 1-inch water gage shall be constructed in accordance with SMACNA HVAC Duct Construction Standards‒Metal and Flexible.
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.
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.
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 Fibrous Glass Duct Construction Standards or NAIMA Fibrous Glass Duct Construction Standards. The air temperature within nonmetallic ducts shall not exceed 250°F (121°C).
The use of gypsum boards to form air shafts (ducts) shall be limited to return air systems where the air temperatures do not exceed 125°F (52°C) and the gypsum board surface temperature is maintained above the airstream dew-point temperature. Air ducts formed by gypsum boards shall not be incorporated in air-handling systems utilizing evaporative coolers.
Flexible air ducts, both metallic and nonmetallic, shall be tested in accordance with UL 181. Such ducts shall be listed and labeled as Class 0 or Class 1 flexible air ducts and shall be installed in accordance with Section 304.1.
Flexible air ducts shall not be limited in length.
Flexible air connectors, both metallic and nonmetallic, shall be tested in accordance with UL 181. Such connectors shall be listed and labeled as Class 0 or Class 1 flexible air connectors and shall be installed in accordance with Section 304.1.
Flexible air connectors shall be limited in length to 14 feet (4267 mm).
Flexible air connectors shall not pass through any wall, floor or ceiling.
The design temperature of air to be conveyed in flexible air ducts and flexible air connectors shall be less than 250°F (121°C).
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 International Building Code.
Ducts shall be sealed and secured prior to pouring the concrete encasement.
Plastic ducts shall be constructed of PVC having a minimum pipe stiffness of 8 psi (55 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 (66°C).
All longitudinal and transverse joints, seams and connections in metallic and nonmetallic ducts shall be constructed as specified in SMACNA 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 inches of water column (500 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.
Exception: For ducts having a static pressure classification of less than 2 inches of water column (500 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.
Provisions shall be made to prevent the formation of condensation on the exterior of any duct.
For structures in flood hazard areas, ducts shall be located above the elevation required by Section 1612 of the International Building Code for utilities and attendant equipment or shall be designed and constructed to prevent water from entering or accumulating within the ducts during floods up to such elevation. If the ducts are located below the elevation required by Section 1612 of the International Building Code for utilities and attendant equipment, the ducts shall be capable of resisting hydrostatic and hydrodynamic loads and stresses, including the effects of buoyancy, during the occurrence of flooding up to such elevation.
Ducts shall not be installed in or within 4 inches (102 mm) of the earth, except where such ducts comply with Section 603.8.
Ducts installed in locations where they are exposed to mechanical damage by vehicles or from other causes shall be protected by approved barriers.
Ducts including linings, coverings and vibration isolation connectors installed on the exterior of the building shall be protected against the elements.
Air dispersion systems shall:
- Be installed entirely in exposed locations.
- Be utilized in systems under positive pressure.
- Not pass through or penetrate fire-resistant-rated construction.
- Be listed and labeled in compliance with UL 2518.
Duct registers, grilles and diffusers shall be installed in accordance with the manufacturer's instructions. 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.
Floor registers shall resist, without structural failure, a 200-pound (90.8 kg) concentrated load on a 2-inch-diameter (51 mm) disc applied to the most critical area of the exposed face.
Diffusers, registers and grilles shall be prohibited in the floor or its upward extension within toilet and bathing rooms required by the International Building Code to have smooth, hard, nonabsorbent surfaces.
Exception: Dwelling units.
Exception: Dwelling units.