Photo 1 of Therwen Backdraft Damper Duct Manual Volume Damper with Sleeve Stove Pipe Galvanized Sheet Adjustment Airflow Ducting Branch HVAC Air Balancing for Range Hoods, Fans(4 Inch, 2 Pcs)

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Photo 1 of Therwen Backdraft Damper Duct Manual Volume Damper with Sleeve Stove Pipe Galvanized Sheet Adjustment Airflow Ducting Branch HVAC Air Balancing for Range Hoods, Fans(4 Inch, 2 Pcs)Photo 2 of Therwen Backdraft Damper Duct Manual Volume Damper with Sleeve Stove Pipe Galvanized Sheet Adjustment Airflow Ducting Branch HVAC Air Balancing for Range Hoods, Fans(4 Inch, 2 Pcs)