Bathroom Exhause Fan Question(s)

[MisterEd]

First of all, thanks for this forum.

Iwant to install a new QUIET fan in our (relatively small 44 SQ FT) master bathroom in a 60yr old home. B/R has a tub/shower. Above the bathroom is an opened attic with insulation on the floor. I currently have an old, noisy, useless ceiling fan installed that has 4" flex (not-insulated) ductwork running from the fan unit to the side wall of the house..

I am looking to installing an inline fan. They seem to be the quietest around. I am looking at the PANASONIC unit which is rated at 120CFM which I know SHOULD be plenty http://www2.panasonic.com/webapp/wcs...odel=FV-10NLF1).

I was also considering the larger 240CFM unit http://www2.panasonic.com/webapp/wcs...odel=FV-20NLF1). All of the reviews I have found rate these fans very highly.

Now it would SEEM that the 120 would be plenty big and the 240 would be way too big which leads to my question.

Is there any problem with using a too large unit (other than it costs more and uses more power)? Will it be too strong so as to not work properly like getting a central A/C unitthat is too big?

Part of the reason I am considering the larger (240cfm) unit is because I will be using 4" or 6" insulated flexible duct (depending on which size unit I choose). The run isn't too long (maybe 25 feet total) but there are a number of unavoidable twists and turns to get to the inline fan from the bathroom ceiling and from the inline fan to the outside wall. There is at least 1 unavoidable close to 180 degree turn and 2 90 degree turns. From everything I have been reading the flex duct itself and the turns greatly increase the static pressure and reduce the efficiency of the fan requiring a more powerful fan.

So what do you'all think? With this situation should I go with the 120CFM or the 240CFM. Cost and power use not withstanding and taking into consideration I have no other option in mounting location of the fan unit so the direction of the ducting can't be changed.

Thanks in advance, I await your expert opinions!