The remodel type fan is installed from inside the room. Be aware you will get some insulation falling during the process.

no access to the attic?

what I ususally do is to go in the attic &
remove existing bath fan.
purchased new fan is always larger..so
opening has to be enlarged.
move insulation back, have someone
inside..holding a box close to sheetrock
ceiling to catch sheetrock pieces & insulation.
this person holds new fan level while person
in attic attaches 'legs' to ceiling joists.
elec is wired in...back draft damper is installed
correctly & vented out of attic.
person inside house uses mastic (hardcast brand
1402 tape) to seal between sheetrock cut and
new bath fan housing.

whisper quiet fan by panasonic is nice..but pricy.
I recently installed the quite fan by broan. not
much difference in sones level..better price.
homeowner liked it so much...I put in 2 more!

best of luck.

I "have" access to the attic but there's a nice fresh layer of loose fiberglass up there that I would prefer not to disturb it at all possible. The other Panasonic fan I installed required access from above and couldn't be put in any other way. That's why I was wondering if they had one that could be put in without going up in the attic.