I've installed two standard-height units in attic-accessible locations and a low profile unit in a downstairs half-bath. The 80 CFM fans, although installed identically, sound different from one another. The 50 CFM unit downstairs is so quiet that I have to walk into the bathroom and listen for it.

I used rigid ducting on all three fans and wrapped all of it in insulation, which is tricky when the ducting is between floors.

My old fans were contractor-grade junk. I had to work with what little romex was available. The fans also have a lip around the body, which prevents them from being mounted right against a joist (unlike the old fans, which had to be mounted that way). This caused some excess size in the cutout that I had to deal with.

The 80 CFM fans pull all of the humidity and steam out of the bathrooms during showers, and the 50 CFM fan is strong enough to make a breeze through the closed door. I very much like these fans.

hey brayton - did you figure out why the two 80's sound different?

i, like kevin, also have the whisper fit, though i had to go down to 3", and it is too loud for me. i turn it on when i leave the room, which is better than nothing, but when i'm using my air tub it sometimes generates steam with all the bubbles, but i can hear the fan over that! still not as loud as a builder grade, but disappointing. I'm debating changing out to 4" ducts (that's what goes out of the house already & for some reason it goes down to 3" inside the attic) and maybe moving this fan into the hall bath & getting a quieter version for mine.

lisa

If you do some research on venting, focusing especially on the NOISE angle, you'll see that there's a lot you can do with the installation to make your fans run quietly -- or NOT so quietly. There are two main componants to vent fan noise: The fan motor, and the noise created by the moving air. There can also be vibration noise if the fan or ducts aren't mounted securely or vibrate against a structural member.

The quiet fan motor is part of what you buy, and in this respect, the Panasonics are very, very good. You can also buy vent systems where the motor is mounted remotely - near the other end of the vent stack, in the attic powering more than one vent, outside on the wall, etc. Those are also quiet, but tend to be more expensive and more complex to install.

But for most installations, the largest noise factor is the ducting itself, and a good duct design and installation will be the single biggest thing you can do to make your vent fan run quietly. Flex ducting is considerably noisier than rigid ducting -- just think of all of those little ripples in the duct walls causing air turbulence, not to mention all of the bends and kinks. Larger diameter ducts are quieter than smaller diameter, and larger radius turns are quieter and more efficient at moving air than tighter turns. And of course, taping and insulating your ductwork reduces noise and the potential for vibration and/or noise transfer from ducts vibrating against studs or rafters.

The attached ductwork planning guide is clear and friendly, and IMO, very useful. It's specifically for kitchen hoods, but the design principles are the same.

Here is a link that might be useful: Ductwork Planning Guide

My two identical fans are mounted one above the tub and one above the commode (but the tub and commode aren't there yet). The one above the tub doesn't have a duct installed and just vents into the attic for now. The one above the commode has 4" flex duct about 4 feet to a roof vent. I think the one above the tub is louder. I am wondering if it is because the exhaust noise is coming back through the ceiling?
I am buying the .3 sone unit for the other bath. I think I need 80cfm for an 8 x 10 bath.
The master bath is about twice the square footage plus has a volume ceiling. I figured to use two or three fans and turn on as many as I need. I have a spot for a third fan but am waiting to see how well two work out.

My 80 CFM fans are installed identically. The 4" rigid ducting is taped with foil tape at every connection. I think what makes the bulk of the noise is that there is a very tight turn in each. It's a tight turn of around 45°, which is terrible, but not something that I could have easily worked around.

The duct runs 3' from the fan in a straight line, then has two turns joined together to start a back-track so the pipe can run back to the roof vent. Rotating the fan 180° in order to eliminate this turn wasn't possible in my situation.

One of the fans was originally connected with two lengths of flexible foil duct, which was not straight or insulated in the least. That one had the same amount of air noise with either duct.

Too bad I couldn't avoid those switchbacks. Oh well, at least it's solid and insulated now.

Our 80CFM Panasonic was also installed with a switchback. I pointed this out to our contractor who said he would correct it. Come to find out he never did. Not only is it louder than our other fans, it seems to not work very well at all. Yup, it's all about installation.

Fortunately the airflow on the fans is still very good. It manages to keep up with our showers with the walls and mirror staying dry.