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Difficulty connecting 4" bathroom fan duct to 3" duct exiting home

413 Views 14 Replies 9 Participants Last post by  530Foreman
So, I'm wanting to install rigid ducting for my new downstairs bathroom fan exhaust.

I thought it was 4" all along, but I'm dumb as it was actually a 3" duct exiting the side of the home!

Wood Gas Concrete Plumbing Metal

Grey Wood Rectangle Roof Brick

So I purchased a 4" - 3" reducer to make the ends meet
Shoe Human leg Personal protective equipment Metal Wood

But now... It seems that my reducers 3" end is the same diameter as the 3" duct in wanting to connect it to
Cylinder Gas Wood Composite material Glass

So... I'm at a loss!
How am I supposed to connect these? It seems like the reducers 3" end is too reinforced to crimp.

My dad says I should just wrap it with foil tape and call it a day.

Any advice is appreciated!
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25 Posts
Discussion Starter · #7 ·
Yes, that's what he means.

This is the right part. By the way by reducing the ducting your fan will not be as quite.
View attachment 718368
Ugh that's true... Come spring, hopefully I'll be able to swap out the 3" end from outside the home, once it's warmer.

Thank you for mentioning that, and confirming my part selection as well!
This stuff is really Greek to m, so you guys are life savers.
It will sure be better than the old white plastic 3" flex tube that use to be there at the very least, I hope

· Registered
253 Posts
crimp the end coming from the dryer. you want the path of air or particles to be smooth in the transition in the direction of the air path.

if you can't crimp it. just tape it man.

Then use a quality metallic duct tape to seal it if possible. that stuff is awesome.

· Registered
166 Posts
I believe the crimp needs to be in the direction of the air flow. That would mean crimping the 3” end on the reducer
You are correct, but he's going to be replacing the damper in the spring with a 4" one, so this will get him through until then and he can eliminate the reducer, which is a bigger problem.
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