Kikerike 2 Pcs 4 Inch Draft Blocker Backdraft Damper Duct Draft Stopper One-Way Airflow Ducting Insert Backflow Preventer Inline Fan Vent Deflector

Excellent design, construction, and workmanship.The shell is made of rigid sheet metal and the butterfly dampers of aluminum. The dampers are normally held in the closed position against the seal by light springs. The dampers open in one direction by just blowing against it. Both ends of the shell fit perfectly inside 4 inch diameter ducting. The plain ends allow it to be easily installed in an existing ducting that needs a backflow preventer. It even had a sticker noting how to orient the dampers properly when installing it horizontally.I used it to prevent wet exhaust from our clothes drier backflowing to our washroom. Both drier exhaust and washroom vent were tied to a tee that exhaust to the outside. Our washroom vent fan damper was not enough to keep moist air from our drier from backflowing into our washroom.

Put a fan in my garage and need a damper. This one is nice had a good seal and the spring opens and closes easily.

Works great!! would buy again

I have allergies and apparently if I leave my portable Danby AC connected to the Window I wake up wheezing with Asthma or rather a type of bronchitis that fills my lungs with mucus from the allergies. Coughing and wheezing throughout the night. I had no idea that a backdraft damper existed or at least I could imagine that it existed but I had to search for "AC Duct air Blocker" to find that what I was looking for was a backdraft blocker. Measured twice the size of my Duct and it turns out that there are only three sizes 4", 6" and 8". My duct was 6.5". When my Draft Blocker arrived and I fitted it into the duct it was loosely fitted so I added a foam seal around the draft blocker and that made the backdraft blocker a tighter fit. Wasn't sure how far to push it into the duct but on the first try I decided to just have it near the entrance of the duct and that should be good enough. Checked that it was closed when my AC is not on and checked that I had Air flow when I turned on my AC by checking outside whether there was hot air blowing out of the exhaust. Yup works wonderfully. SOOOO theoretically without the outside air flowing through my AC duct I should have a good sleep tonight. I love how that if I have a problem such as a Backdraft on my AC Duct that I could find it on Amazon.

No ussues, pretty good reverse flow prevention. Has a light spring to allow various mounting angles but careful not to deform while attaching hose or the flapper motion can he impeded. I used aluminum duct tape rather than hose clamps.