I am intrigued by the rave reviews the Panasonic bathroom fans get, and would consider trying one out. I wonder about the install, though. I have not done this before except to replace one fan with another of equal and that was in a different bath. My current fan in this bath is something like 7x7 and it looks like the Pannys are about twice that size. I have never looked at the top side of the current fan, but I know it is way over at the edge of the roof with a lot of blown in insulation between the door to the attic and the fan, so working there might be hard. And, I don't know how these fans are attached... would it be unrealistic to expect that there is room up there to replace a 7x7 fan with one that is 13 x 13? Thanks.
No, it is easy to do, provided you can get access to the attic. Not really any good way to accomplish it from below. The only space limitation would be obstructions in the attic such as framing, but a common ceiling joist spacing is 16"oc, which will certainly allow installation of any bath fan.
It is no fun working in the attic, but that's how it has to happen.