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.