C403.7.8 Shutoff dampers. Mechanical openings shall be provided with shutoff dampers in accordance with Sections C403.7.8.1 through C403.7.8.4.
C403.7.8.1 Shutoff dampers for building isolation. Outdoor air supply, exhaust openings and relief outlets and stairway and elevator hoistway shaft vents shall be provided with Class I motorized dampers. See Sections C403.10.1 and C403.10.2 for ductwork insulation requirements upstream and downstream of the shutoff damper.
EXCEPTIONS: | 1. Gravity (nonmotorized) dampers shall be permitted in lieu of motorized dampers as follows: |
| 1.1. Relief dampers serving systems less than 5,000 cfm total supply shall be permitted in buildings less than three stories in height. |
| 1.2. Gravity (nonmotorized) dampers where the design outdoor air intake or exhaust capacity does not exceed 400 cfm. |
| 1.3. Systems serving areas which require continuous operation for 24/7 occupancy schedules. |
| 2. Shutoff dampers are not required in: |
| 2.1. Combustion air intakes. |
| 2.2. Systems serving areas which require continuous operation in animal hospitals, kennels and pounds, laboratories, and Group H, I and R occupancies. |
| 2.3. Subduct exhaust systems or other systems that are required to operate continuously by the International Mechanical Code. |
| 2.4. Type I grease exhaust systems or other systems where dampers are prohibited by the International Mechanical Code to be in the airstream. |
| 2.5. Unconditioned stairwells or unconditioned elevator hoistway shafts that are only connected to unconditioned spaces. |
C403.7.8.2 Shutoff dampers for return air. Return air openings used for airside economizer operation shall be equipped with Class I motorized dampers.
C403.7.8.3 Damper leakage rating. Class 1 dampers shall have a maximum leakage rate of 4 cfm/ft2 (20.3 L/s x m2) at 1.0 inch water gauge (w.g.) (249 Pa) when tested in accordance with AMCA 500D and shall be labeled by an approved agency for such purpose. Gravity (nonmotorized) dampers shall have an air leakage rate not greater than 20 cfm/ft2 where not less than 24 inches (610 mm) in either dimension and 40 cfm/ft2 where less than 24 inches in either dimension. The rate of air leakage shall be determined at 1.0 inch w.g. (249 Pa) when tested in accordance with AMCA 500D for such purpose. The dampers shall be labeled by an approved agency. Gravity dampers for ventilation air intakes shall be protected from direct exposure to wind.
EXCEPTIONS: | 1. Gravity (nonmotorized) dampers are not required to be tested to verify the air leakage rating when installed in exhaust systems where the exhaust capacity does not exceed 400 cfm and the gravity damper is provided with a gasketed seal. |
| 2. Motorized dampers on return air openings in unitary packaged equipment that have the minimum leakage rate available from the manufacturer. |
C403.7.8.4 Damper actuation. Outdoor air intake, relief and exhaust shutoff dampers shall be installed with automatic controls configured to close when the systems or spaces served are not in use or during unoccupied period warm-up and setback operation, unless the systems served require outdoor or exhaust air in accordance with the International Mechanical Code or the dampers are opened to provide intentional economizer cooling. Stairway and elevator hoistway shaft vent dampers shall be installed with automatic controls configured to open upon the activation of any fire alarm initiating device of the building's fire alarm system or the interruption of power to the damper.