Reduce bathroom fan vent from 4" to 3"?

anniel89July 20, 2014

I need to install a basement bathroom fan. It will run about 1 1/2 feet and out the wall. I'm pretty sure I have enough space for a 4" vent but I may only have enough for a 3".

I haven't found a fan/light with a 3" vent. Can I reduce from a 4" to a 3"? If so, should I look for a fan with higher cfm (or lower?)? It's not a very long run - any thoughts would be appreciated.

Thank you for reporting this comment. Undo
snoonyb

There are 4" to 3" reducers available at most hdw. stores and for that short a run, you shouldn't affect the efficiency.

    Bookmark   July 20, 2014 at 1:51PM
Thank you for reporting this comment. Undo
kudzu9

You can also transition from 4" round to oval, and then back to round where it connects to the outside cap. The oval shape easily fits inside a wall and you can maintain the same cross-sectional area. Even Amazon carries a variety of oval duct and fittings. Below is one example that is used for a dryer, but you could use it with a fan as well. Or you could just get fittings and make up your own to fit your situation.

Here is a link that might be useful: Round-to-oval-to-round periscope duct

    Bookmark   July 20, 2014 at 2:46PM
Thank you for reporting this comment. Undo
anniel89

Thanks folks! Mostly I'm worried about the space where it exits the house. I have just about 4" if I'm lucky between the subfloor of the main level and the concrete porch outside. I'm trying to squeeze the vent in that space.

If I can go down to the 3" without damaging the fan it will be no problem.

    Bookmark   July 21, 2014 at 10:26AM
Thank you for reporting this comment. Undo
snoonyb

However, finding a dampered vent cap may be difficult. So you might need to end it at the siding with a flat screen, and no damper.

    Bookmark   July 21, 2014 at 2:34PM
Thank you for reporting this comment. Undo
kudzu9

Amazon has several dampered vent caps...this one for example:

Here is a link that might be useful: Broan, 3

This post was edited by kudzu9 on Wed, Jul 23, 14 at 5:20

    Bookmark   July 23, 2014 at 5:14AM
Sign Up to comment
More Discussions
Crawlspace floods with water, but it doesnt touch the wood, ok?
I have a crawlspace that is about 2 ft from the ground....
tlbean2004
Help with rough, ugly laminate counter edges
Hello, we recently put in new laminate countertops...
Elizabeth Loparco
Craftsman Garage Door opener won't close
Hello, Wife came home today and was able to open garage...
mattb32
Roof leaking due to antique bricks? (X-post with Bldg a Home)
Good morning! We are having a problem with our new...
cvazqu
Insulating an inaccessible crawl space?
My 1940s bungalow style house sits on a crawl space...
blessedbe
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™