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Still trying to solve my problem of bathroom vent fans that aren't vented anywhere...

Was considering running out the gable, but that's 25' away, plus another 10-15' of duct and a couple of elbows to move from the outside edge of the attic into the center (and up so that I can slope the duct towards the exhust port?)

Trying to figure out if that's a good idea or bad.

Ran across this great answer... How much vent fan throughput do I need for my bathroom? enter image description here Which as I read it, basically says...the longer the duct, the higher CFM needed. So given my 480 cu. ft. bathroom and estimated equivalent duct length I'd probably need a 70-90cfm fan.

But searching the web also lead me to IRC table M1506.2 Duct Length, which I understand to say that a higher CFM also needs a larger duct.

So I think I'd need to use 6" duct, rather the then 4".

IRC table M1506.2

Am I missing something? Confused as to why the answer above seems to penalize 6" (flex) duct when the IRC seems to indicate 6" is a requirement.

enter image description here

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  • What kind of roof do you have??? – JACK Nov 16 '19 at 18:41
  • Asphalt shingles.... Reasons against roof vent... There's already a few things in the same area... Live in Utah, worried about it being covered by snow. Lastly, I hate getting on top a two story... Especially working by the edge :) – Charles Nov 16 '19 at 19:32

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