Deflecto Duct Increaser and Reducer, Plastic Inline Adapter, White, 4” to 3” (IRB43)

Used to decrease 4 to 3 inch exhaust fan duct. Perfect.

As others have said the 4 inch side is the same size as the 4" outlet duct on newer bathroom vent fans BUT I used a hot glue gun to essentially "weld" the two plastic pieces together. To assure a strong connection I wrapped the joint afterward with silicone self adhesive tape. I imagine duct tape would also work. The existing 3" flexible duct was a snug fit, but with a little effort it went over the 3" side of the reducer. I considered using a galvanized steel 3x4 duct adapter (Home Depot, Menards) but because of all the shower moisture being vented out I was concerned with the piece rusting over time. The plastic reducer was cheaper and will be rust-free.

Worked as described. Was used to convert a 3in bathroom exhaust to a 4in. Pretty straight forward item.

It worked for what I needed, Showed up fast and was priced right

The size if the reducer is the same size as the flex duct. I had to cut the duct for it to slide over and then use duct tape to keep together. On the fan side, it was also the same size. I did not have the option to cut. So I have to be creative. :(

Awesome little adapter, It bridged the gap perfectly!!! I wasn’t paying attention when I ordered my vent and got a 4” one when everything else I was using was 3”. Very easy to install.

I bought this to take the 4" output of a bathroom exhaust fan to a 3" flex duct. Even though it is sold as a reducer, the 4" diameter is exactly the same as the fan output and the 3" diameter is exactly the same as the flex duct - Nothing slides onto anything!

Fits perfect