I have a bathroom fan that used to be vented by flexible aluminum
ducting through the soffit. But I was getting ventilated soffits to
work with an attic ridge vent and it seemed ill advised to dump all
that humid air right under the soffit vents. So I switched to a roof
vent.

When I ran the ducting for the roof vent I used rigid aluminum ducting
instead of the flexible stuff, since I always read that the rigid
ducting has a lower resistance to air flow. I used a 1 foot section of
flexible ducting right at the fan exhaust port and then about 1 foot
more of rigid ducting, and then an 80 degree angle bend up to the roof
(about 2 ft) and then a 40 degree angle bend or so to connect to the
roof cap.

The fan itself is a quiet fan. And with flexible aluminum ducting out
through the soffit it was quiet. You basically couldn't hear the fan
if you weren't in the bathroom. But with the rigid aluminum ducting it
is much louder. What can I do to quiet the rigid duct? Or is the only
quiet solution to rip out the rigid duct and use a flexible duct
instead?

The fan itself is a quiet fan. And with flexible aluminum ducting out
through the soffit it was quiet. You basically couldn't hear the fan
if you weren't in the bathroom. But with the rigid aluminum ducting it
is much louder. What can I do to quiet the rigid duct? Or is the only
quiet solution to rip out the rigid duct and use a flexible duct
instead?

Glue something heavy to it, like sheet-rubber.

wrote:

....
When I ran the ducting for the roof vent I used rigid aluminum ducting
instead of the flexible stuff, since I always read that the rigid
ducting has a lower resistance to air flow. I used a 1 foot section of
flexible ducting right at the fan exhaust port and then about 1 foot
more of rigid ducting, and then an 80 degree angle bend up to the roof
(about 2 ft) and then a 40 degree angle bend or so to connect to the
roof cap.

The fan itself is a quiet fan. And with flexible aluminum ducting out
through the soffit it was quiet. You basically couldn't hear the fan
if you weren't in the bathroom. But with the rigid aluminum ducting it
is much louder. What can I do to quiet the rigid duct? Or is the only
quiet solution to rip out the rigid duct and use a flexible duct
instead?

How did you mount the duct? Sounds (so to speak ) like it's acting
as a drum. Try mounting it on isolated mounts--either hang it w/
something like plumbers tape or use a soft washer between the hard mount
point and the duct to isolate it.

Wrapping it like a water heater blanket could help, too (as well as
minimize condensation).

wrote in message
oups.com...
I have a bathroom fan that used to be vented by flexible aluminum
ducting through the soffit. But I was getting ventilated soffits to
work with an attic ridge vent and it seemed ill advised to dump all
that humid air right under the soffit vents. So I switched to a roof
vent.

When I ran the ducting for the roof vent I used rigid aluminum ducting
instead of the flexible stuff, since I always read that the rigid
ducting has a lower resistance to air flow. I used a 1 foot section of
flexible ducting right at the fan exhaust port and then about 1 foot
more of rigid ducting, and then an 80 degree angle bend up to the roof
(about 2 ft) and then a 40 degree angle bend or so to connect to the
roof cap.

The fan itself is a quiet fan. And with flexible aluminum ducting out
through the soffit it was quiet. You basically couldn't hear the fan
if you weren't in the bathroom. But with the rigid aluminum ducting it
is much louder. What can I do to quiet the rigid duct? Or is the only
quiet solution to rip out the rigid duct and use a flexible duct
instead?



Is it possible that when you installed the new duct you accidentally caused
the damper flap to not open? Try removing the fan motor and stick your hand
up there to see if the flap is moving freely. If the air cannot blow out
the duct the fan will make more noise than usual.

as we get older and fussier about sones, it's time to spend the $200 on
the exhaust fan inline in the attic itself.

look at the fan options at

http://www.energyfederation.org/cons...p/cPath/30_406

interesting other options for energy saving at
http://www.efi.org/

I listened to the fan some more last night and while it's definitely a
lot louder than it used to be with the flexible duct vented out the
soffit, I may be misleading when I describe it as "very loud". It's
all relative. The noise sounds kind of like air flow in the duct.
It's a kind of echo like sound, a sort of howling sound. The damper
flap is not stuck.

Regarding an exhaust fan inline, I had such a fan in my kitchen. It
was extremely loud. The new panasonic fan is rated 2 sones and was
VASTLY quieter than the inline fan before I connected the ducting to
the roof, and still definitely much quieter with the ducting hooked up.
The ducting did make it a lot louder. If the ducting is a source of
noise I don't understand how moving the fan to a different site will
help as you still need ducting. Both the fan in my kitchen (which is
not the topic of this post) and the fan in my bathroom (which is the
topic of this post) are very quiet fans when there is no ductwork.
Both of them got quite a bit louder when I attached rigid ductwork.

But the bath fan (which is rated at 0.8 sones) was very quiet when it
was vented via flexible ducting out the soffit and is significantly
louder now. The fan was the same. Getting an inline fan is clearly
not necessary to make it quiet because the fan I have used to be quiet
with a different duct configuration. Could the problem be the roof
cap. There was an intermediate configuration where the fan was
connected to the roof cap with a serpentine run of flexible duct that
made a 90 degree turn right at the fan exhaust port (bad!). This was
also louder than the old setup that ran to the soffit, but not as loud
as the rigid duct.

I did some testing to assess whether the fan noise due to the rigid
ducting had to do with the mounting or support of the rigid duct. I
had my wife listen to the sound of the fan while I held parts of the
ductwork to damp any vibrations. Nothing I did to the ductwork made
any difference. So attaching a rubber sheet to the ducts will
presumably have no effect. (It's got less mass than I do.)
It almost seems like the only thing that could have an effect would be
something that alters the air flow pattern.