Bathroom fan vent diameter

Users who are viewing this thread

DIYJared

New Member
Messages
7
Reaction score
0
Points
1
Location
Portland, OR
Hi All,
Been using this forum for a while and it has been very helpful!

I'm remodeling our two bathrooms and had the plumbing inspection today (all good). One thing he did mention though was that the two bathroom fan exhaust vents were too small (4" flexible). He said Oregon code was 5" rigid (preferred) or flexible and all less than 25' in length. I found a site for Oregon codes (http://www.cbs.state.or.us/bcd/programs/online_codes.html), but I can't seen to find reference to 5" diameter pipe. It's not that I don't believe him, but I'd like to know how to look these things up in the future.

Thanks for any hints or info...
Jared
 

Hackneyplumbing

Homeowner
Messages
63
Reaction score
0
Points
0
Location
Alabama
I found it in the oregon residential Specialty Code Chapter 16 Table M1507.4 perspective exhaust duct sizing.

Some inspectors think they can make their own rules instead of following the written law.
 

DIYJared

New Member
Messages
7
Reaction score
0
Points
1
Location
Portland, OR
Ah, cool...thanks! I see it now. Looks like you can use 4" (rigid) with a 80cfm fan, but only if it is 20' or less.

Thanks again - appreciate the guidance...
 

hj

Master Plumber
Messages
33,602
Reaction score
1,038
Points
113
Location
Cave Creek, Arizona
Website
www.terrylove.com
Some inspectors use the "rule of thumb" they are used to instead of referencing the code as it is written. The size/capacity of the fan and the length should dictate the pipe size.
 

Jadnashua

Retired Defense Industry Engineer xxx
Messages
32,770
Reaction score
1,190
Points
113
Location
New England
Smooth ducting has much less backpressure than corrugated stuff, and larger diameter stuff flows better than smaller ducts (might seem obvious, but it all factors in).

FWIW, the instructions on my bathroom vent called for 6" ducts. Larger ducts can allow a bigger diameter fan, which can move as much air, but do it more quietly than a smaller one running faster and with more turbulence.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks