calimaero® 4 Inch Backdraft Exhaust Damper Seal One Size Fits All Duct Backdraft Damper Gravity Powered Made in Germany HVAC Damper Dryer Vent Valve Keep Cold Air Out

I needed a one-way valve for the air vent on a project of mine and this fit the bill. It fits nicely into a 4” duct pipe and obstructs backwards flow nicely. This works perfectly.

I did not like the fact that the hard plastic is undersized about 1/8 inch and once I installed it correctly at 90 degrees to 4 “ duct that it had about 1/8 gaps left and right with duct seam at top. They need to enlarge plastic 1/8” and then with the two outer diameter gaskets you will have to jam the damper into the duct for a nice tight fit. Which means minimal cold air leakage back into my bathroom!Also the skinny black plastic bar that holds the rubber flapper in place has no integrity to me( I am a longstanding mechanical metal and wood guy with BSME degree ). I seriously doubt this will last thru several winters up north in WI.By a metal backdraft damper assembly instead of this el cheap attempt of a damper. I simply do not believe the damper material, nor skinny plastic holding it in place will survive for years in deep north or south.

I was looking for a back flow preventer with minimal pressure drop that would seal tightly. I live in a condo with an ducted exhaust that sometimes has reversals that can bring smoke or odors into out unit. Out of the box the flapper was puckered but I was able to cut small notches to allow it to lay flat.life is compromise an I could not mount vertical because the weight of the flapper made it open and I was afraid it would not close for minor reversals. I was able to install it horizontal which appears to work pretty good.

I needed this at the end of a 20 foot run of flexible duct. It fit perfectly in the 4 inch plastic flange I installed in the wall. I agree with other reviews that the plastic bar holding the rubber flap in place is pretty flimsy. I used some Loctite Fun-Tak Mounting Tabs to secure it. The manufacturer should have used a stainless steel spring instead of the plastic bar. The damper works great for me. 105 CFM bathroom fan pushes the rubber flaps open easily and absolutely no backdraft when the fan is off. I will buy this again.

Really cheap. Maybe it could be modified to work, but on its own, it is pretty useless. I like that it is slim, but that's about it.

Update: went from 5 stars to 1 star. The flexible plastic that’s designed to seal has warped after one year. It needs a new flap, but I have no way to get one.I originally bought this because the exhaust from the microwave had a metal exhaust trim with a flapper that would make noise nonstop on windy days.I removed the metal flap and placed this in its place. It works perfect for that. I’ve had it installed for about 1.5 years at this point.Although it is thin and doesn’t feel commercial, it does what it’s designed to do. I’d pay a little extra for something stronger, but then again it isn’t exerted to any extreme wind speeds from the house. They are made from a plastic (PVC?) skeleton and it has a thin rubber flap.I since purchased another 2 to place on the other exhausts from bathrooms. They work perfect for this application.

Excellent product If you can’t fit a typical damper in old construction, flexible duct work (or dont have full access). This was exactly what I needed! It’s only 1/2 thick so you can wedge it right into the exposed duct without having to tear everything out.

I was a little skeptical of the mechanism but was lured by the thin dimensions. The product I received is basically junk. It is not as pictured. The flapper is not black plastic or rubber, but rather this light brown, very thin, very flimsy rubber. It doesn't have enough stiffness to even overcome gravity if the flapper is facing downward, and when facing upward the flap doesn't sit flat (I tried adjusting it a bit, as it's just friction-fit in place, but it is just too thin and cannot be made to sit flat).I don't consider this the same product pictured, and this substitute does not even function.