On 12 Sep 2006 07:58:42 -0700, wrote:

I am installing an exhaust fan in my bathroom, which will vent through
the roof about 2.5 feet above the unit. I have an exhaust hood in my
kitchen, and when I stand by the stove I can hear the traffic out back
because the outside vent on the roof faces the traffic and acts like a
collector to bring the noise into the house.

My bathroom vent will also face the road, and I don't want to carry
that noise into the house. What kind of duct will be the quietest? I
think the thin, ridged metal tubing would be the loudest. I'm thinking
the flexible stuff (like dryer vent hose) will be quieter? I know it
has more resistance but its a short run and the fan is plenty powerful
for the room its in. But I was definately going to insulate the pipe,
is the flexible stuff insulated? It felt pretty thin when I was
looking at it in the store.

Also I was planning on getting a plastic vent for the roof, I think
that should be quieter than a metal one?

Thanks for any help.
-Ryan

You are on the right track.

You should check for the one way flapper if you hear traffic while
the fan is off. Since you have a powerful fan, you can add another.

Modify the roof appliance and shield the side facing the traffic.

And the flexible duct for hvac will also dampen the sound
substantially.