# Fred # wrote:
Wife purchased three of the quiet Broan QT080L bathroom exhaust fans with
light and night light. I tested it out on the kitchen table and it was quiet
so then I proceeded with the installation in the downstairs 1/2 bathroom.
The bathroom is down to studs and subfloor with all insulation removed for
remodel. The Broan has a 4" duct connection but the house has 3". Once
everything was connected, the fan wasn't all that quiet. The noise was from
both fan vibration and wind. Its still more quiet than the old noisy fan
but I could hear the new fan from upstairs. The mounting is solid to joist
per instruction and the connection to the 3" duct is tight. I suppose once I
close up the ceiling and walls with insulation it would not be as bad. Are
quiet fans really all that quite? Maybe should have purchased Panasonic fans
instead - its the same price.

I expect Bob has already hit on the two prime areas --

Might just try it by disconnecting its outlet from the 3" ductwork
temporarily and see if the noise is reduced. I'm guessing it will be
and to get the benefits of the fan you'll need to install larger duct.
Don't see could go wrong in going to 6" even although probably no
real advantage as the outlet is 4". In doing so, though, avoid the
flexible ribbed wall stuff as the rough surface adds to turbulence
which raises noise. If you absolutely need some for a connection, make
it as short as possible. And, of course, make sure the ductwork is
mounted securely so it doesn't add its own vibration.

If, otoh, what you then hear is actually the fan itself running and not
airflow, I'd look at adding some dampening between it and the joists.
A section of tire sidewall is one of my favorite things to use for such
isolators.

Finally, if you do add insulation or other sound-deadening around it,
be sure to not block any necessary air circulation for cooling of motor
and lights, if any. Don't want a quiet installation to become a fire
hazard!