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M1601.1 Duct Design
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Duct systems serving heating, cooling and ventilation equipment shall be installed in accordance with the provisions of this section and ACCA Manual D, the appliance manufacturer's installation instructions or other approved methods.
Above-ground duct systems shall conform to the following:
- Equipment connected to duct systems shall be designed to limit discharge air temperature to not greater than 250°F (121°C).
- Factory-made ducts shall be listed and labeled in accordance with UL 181 and installed in accordance with the manufacturer's instructions.
- Fibrous glass duct construction shall conform to the SMACNA Fibrous Glass Duct Construction Standards or NAIMA Fibrous Glass Duct Construction Standards.
- Field-fabricated and shop-fabricated metal and flexible duct constructions shall conform to the SMACNA HVAC Duct Construction Standards—Metal and Flexible except as allowed by Table M1601.1.1. Galvanized steel shall conform to ASTM A653.
- The use of gypsum products to construct return air ducts or plenums is permitted, provided that the air temperature does not exceed 125°F (52°C) and exposed surfaces are not subject to condensation.
- Duct systems shall be constructed of materials having a flame spread index of not greater than 200.
Stud wall cavities and the spaces between solid floor joists to be used as air plenums shall comply with the following conditions:
- 7.1. These cavities or spaces shall not be used as a plenum for supply air.
- 7.2. These cavities or spaces shall not be part of a required fire-resistance-rated assembly.
- 7.3. Stud wall cavities shall not convey air from more than one floor level.
- 7.4. Stud wall cavities and joist-space plenums shall be isolated from adjacent concealed spaces by tight-fitting fireblocking in accordance with Section R602.8.
- 7.5. Stud wall cavities in the outside walls of building envelope assemblies shall not be utilized as air plenums.
- Volume dampers, equipment and other means of supply, return and exhaust air adjustment used in system balancing shall be provided with access.
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 to 14 | 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.
Underground duct systems shall be constructed of approved concrete, clay, metal or plastic. The maximum design temperature for systems utilizing plastic duct and fittings shall be 150°F (66°C). Metal ducts shall be protected from corrosion in an approved manner or shall be completely encased in concrete not less than 2 inches (51 mm) thick. Nonmetallic ducts shall be installed in accordance with the manufacturer's instructions. Plastic pipe and fitting materials shall conform to cell classification 12454-B of ASTM D1248 or ASTM D1784 and external loading properties of ASTM D2412. Ducts shall slope to a drainage point that has access. Ducts shall be sealed, secured and tested prior to encasing the ducts in concrete or direct burial. Duct tightness shall be verified as required by Section N1103.3. Metallic ducts having an approved protective coating and nonmetallic ducts shall be installed in accordance with the manufacturer's instructions.
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