Section 603 Duct Construction and Installation
ROUND DUCT DIAMETER (inches) |
STATIC PRESSURE | |||
1/2-inch water gauge | 1-inch water gauge | |||
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 gauge | 1-inch water gauge | |||
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 |
- Ductwork that exceeds 20 inches by dimension or exceeds a pressure of 1-inch water gauge 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.
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. 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. This exception shall not apply to snaplock and button-lock type joints and seams located outside of conditioned spaces.
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.
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.