You should go to the Panasonic ventilation site which has a calculator section to determine which model is appropriate.

They add the height of the bathroom, the duct diameter that you have ijn place, and how mnay elbows (from 0-whatever) are in your ductwork.

Then they will give you a selection of fans with or without lights that fit your needs.

Greg

I put a 150CFM Panasonic in my bathroom which is smaller than yours (5'X7'). I know that it moves more air than recommended, but I like that. It gets the moisture our quicker and completely removes smells before they have a chance to enter the rest of the house.

The only downside is that it pulls out the "conditioned" (heated and cooled) air from your home, but you could regulate that by changing how long you keep the fan on for. Buy a good timer to control the fan so that it stays on for about 5-10 minutes after a shower and a "Number 2".

Actually replacing the fan could be hard if you never did it before.