The following factors are to be considered to avoid affecting airflow.  

1. Obstructions. Obstructions near the fan inlet or outlet, such as dampers, elbows, duct transitions, guards, etc. Usually, 2.5 duct diameters (about 2.5 wheel diameters) are allowed to be kept away from the two ends of the fan.

2. If the damper is too close to the inlet or outlet, it will result in uneven air flow.

3. Additional guards. Adding additional guards limits the airflow through the fan. Avoid using expanded metal guards; use thin wire guards whenever possible.

4. Avoid using elbows and transitions directly after inline fans. Instead, use the side discharge option for commercial inline fans, which is a good solution. The fan acts as an elbow - air is discharged from the side of the fan to prevent poor outlet conditions.

5. If the damper is placed too near the impeller of the sidewall fan, vibration will be caused. A common practice is that the distance between the damper and the impeller should be made at least one half of the impeller diameter.

6. Make sure that the wheel is running in the right direction. For a backward inclined centrifugal fan, air can still be exhausted even when the wheel is rotating backwards. Keep in mind that the direction of rotation of a 3-phase motor can be changed by reversing two of its stator leads.  

7. As you wire the fan motor and damper actuator, make sure that the wiring is operating correctly to prevent it from getting stuck in the damper, which prevents normal operation.

8. To ensure proper performance, a distance of at least one inlet diameter shall be made between inlet and a wall or housing for fans with no inlet duct.