Fantech PBV4 damper box with 7 Inch ceiling grill for 4 inch duct

As an air distribution device it appears it will work. The integral backdraft damper is another story. Why bother. I have to tilt the unit 30 degrees to get the damper to close under its own weight. I expect a backdraft damper to CLOSE when the fan is off and not rely on back pressure (cold outdoor air) to do the job. Poor design/assembly of this unit and now I have to purchase a separate backdraft damper to do the job I expected this unit to do.