MIVIDE 2Pack 4 inch Backdraft Damper Duct, One Way Airflow Ducting Insert for Ducting in Range Hoods, Bathrooms Fans and kitchen Fan

Great quality and works perfect

These worked great. The gasket keeps any flow from backdraft Just note that they only fit over female end.

I elected to vent two bathroom exhaust fans through a single roof vent. I installed these backdraft dampers to ensure exhaust from each bathroom traveled out the roof vent and didn't travel into the other bathroom. These dampers appear to meet my objective. I didn't venture onto the roof to see how much air volume is exiting the roof vent, but I ran each fan individually and checked the non-running fan opening for an signs of air movement from the fan into the room and didn't detect any. You need to install these dampers in a horizontal position and that took a few minutes to get right in my situation. Other than that , they installed easily with some clamps and foil tape.

Perfect solution to this type of problem. High quality, simple, affordable.

They work perfectly

I used these to prevent back flow when I joined 2 seldom used 4” vents together with a “Y” fitting. Nice quality and works well.

It initially worked as intended but after I turn the vent off the weak spring wasn't strong to push the dampers back in place fully. I would look elsewhere, as it kind of defeats the whole point of having a one way airflow if it don't stop the air flow from coming back.

Easy to install perfect for a 2dryer home. Keeps them from steaming up when one or the other isnt running