Kikerike 6 Inch Draft Blocker Backdraft Damper Duct Draft Stopper One-Way Airflow Ducting Insert Backflow Preventer Inline Fan Vent Deflector

Each time the A/C or furnace kicked on it would draw outside air in through the vent hood. Cold in the winter and hot in the summer. The temperature under the hood was significant and very noticeable. So I installed this draft blocker in the pipe in the attic, separating the pipe at a joint inserting the valve and reconnecting the pipes. I seal the joints with aluminum tape. The draft blocker has a weather strip inside sealing it when not in use. I did have to reseal the pipe where it passed through the roof with roof tar to restore the water seal. It works great, the is no back draft now when the A/C is running and made a huge difference. I would recommend and buy again.

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.

works great, as advertised

Good quality - feels like it will hold up to regular use. We attached it directly to the outside vent which has louvers. Since the flaps open proud of the outside opening, we taped it so the flaps would not bump up against the flaps while in use. I feel like I should use some sheet metal screws to hold it, but the fit is snug and the tape seems to hold it all together.

Works well, makes a tight seal, no tapping sound when the flaps close, a little undersized for 8 in hvac. But not so much that some hvac tape couldn't seal it. Easy to install. Seems like it will hold up for a long time. Decent damper for the price.