for quietest installation the fan goes in the attic and the intake
feeds to it from the bathroom.
see:Bathroom Exhaust Fans:
http://www.energyfederation.org/cons...hp/cPath/30_85
"A sone is a measure of loudness. The higher the sone rating the louder
the sound.
Understanding how loud an exhaust fan will be can be difficult, largely
because bathroom exhaust fans are measured in sones, while most common
noise levels we are familiar with are measured in decibels.
Scientifically, one sone equals 40 phons, which is the loudness of a
1,000 hertz tone at 0 decibels above our threshold hearing level. The
relationship between phons and decibels is not one-to-one (affected by,
for instance, frequency), but for our purposes we will assume that
decibels are roughly equivalent to phons. The chart below compares the
sound level of a sampling of exhaust fans with the sound level of a
number of other common sounds.
Sone

0.3
Panasonic 60 cfm FV05VQ2 Fan
0.5
30 Phons
0.5
Rustling Leaves
1.0
40 Phons
1.0
A Quiet Refrigerator
1.5
Panasonic 100 cfm FV11VQ2 Fan
2.0
50 Phons
2.0
Quiet Home
3.0
Panasonic 380 cfm FV40VQ3 Fan
3.0
Normal Office
4.0
60 Phons
4.0
Nornal Television Volume
Note that two sones are twice as loud as one sone, three sones are
twice as loud as two sones, four sones are twice as loud as three
sones, and so on."


Steven wrote:
Hi,
I am looking to upgrade the cheap builder installed exhaust fans in my
bathrooms. They are incredibly loud.
I can find lots of nice quiet ones, but they all required 4 inch (or
greater) ducts. The only 3 inch duct vents I can find are...cheap and
loud.

Does anyone know of a decent fan that will work with 3 inch ducts?

Thanks
Steven