Get a panasonic, nothing else. I think on their website they have a sizing blurb that tells what size you need.

Susan,

With a shower that large you're getting in the 150-175 cfm range.

One fan will require a 6" duct, and asking one fan to move that air can be noisier than two.

With a large bath it's sometimes best to go with two exhaust vents, one in the shower (unless it is a steam shower) and the other outside the shower.

When going with two exhausts, the choices are then to run them individually or coupled.

If your concern is noise, the best way to assure yourself of a quiet installation is to go with a remote fan. The fan unit is located up in the attic, or several feet from the opening in the bath. This distance prevents fan noise from being transmitted through the duct or fan housing itself and into the bath.

In addition, remote fans are quieter in regards to turbulent air noise due to non-remote fans having bends in the exhaust duct located too close to the fan motor.

Personally I'd skip Nutone.

Panny makes some nice fans. They make remote fans as well.

But my first choice for a large bath like yours would be a single Fantech unit pulling air from two exhaust grids. One exhaust grid in the shower, one outside the shower. I'd recommend the PB-230-2. You'll only need 4" duct from each exhaust grid to the fan, then 6" from the fan to the roof/wall exhaust.

Has your contractor done duct loss calculations? If not, your contractor may say at 230cfrm it's oversized, but when you drop down into the .4 to .6 static range, it's about 170-200 cfm.

It'll move air and be quiet doing so.

I highly recommend adding a timer so when you get out of the shower and turn the fan off it automatically keeps running for another 20-30 minutes or so, then turns off on its own.

Mongo

Mongo has some great advice. If you don't like noisy fans, all I can say is to get the quietest fan you can find. In my opinion none of the ceiling mount fans including the Panasonic are quiet enough for a quiet soak in a tub.
I turn my .3 sone Panasonic fan off when I really need to relax.

Thank you for the advice, Mongo!!! I really, really appreciate your taking the time to explain all of that to me. Ventilation is a very important issue and I want to make sure it gets done right. What you explained about getting a single remote unit with two exhaust grids makes sense to me. I think that's the way I want to go. I want to make sure I understand one thing, though...are you saying that a remote fan needs to be sized larger than a normal fan? I want to make sure I clearly understand the reason so I can talk to the contractor without sounding like an idiot. Also, I am curious, what is it that you don't like about Nutone? If I went with a Panasonic remote instead of the Fantech remote you mentioned, is there a particular Panasonic you would recommend for my room?

Susan,

It's not that a remote fan has to be sized larger than a normal fan. It's that a fan just needs to be properly sized.

Period.

And if you have to choose between slightly smaller and slightly larger, I'd recommend larger.

Small baths are typically sized by the volume of the room. Larger baths can also be sized by the fixtures within that room.

Smaller baths can still effectively vent with a single vent. Larger baths can be more effectively vented with more than one vent.

You'll find many people look at the volume of the room (say 150 ft) and then specify a 150 cfm fan to give you one air change per hour. However, that fan, while rated at 150cfm, won't move 150 cfm of air due to the resistance of the ducting, the number or bends in the duct, etc.

Solid 4" metal duct offers less resistance to air movement than the ribbed flex duct. More bends offer more resistance than straight ducting. These inefficiencies mean that your 150cfm fan is now, in reality, only moving 120cfm, or 100 cfm, or 90cfm.

To make up for that added resistance, the fan needs to be upsized. Some of the better manufacturers have always considered basic duct resistance in their calculations.

With the Fantech, it's rated at 230 cfm. However, Fantech realizes that the basic static resistance due to basic run of ducting is .4 pull, so the effective volume of air that the fan can move is actually about 195-200 cfm. Add a couple of more bends, or extra feet of straight run, or ribbed flex versus the smother solid wall duct, and you can get up to .6, then you're only getting about 170 cfm of real air movement.

Nutone? If I needed a fan for a powder room, I might be persuaded. But for good quiet ventilation, Panny's are good, they're quiet too. For larger volumes of air and with only using a single fan, Fantech remotes are better, and quieter.

Do realize that it's sometimes tough to spend extra money on ventilation. Until you realize that your existing fan can be so loud that you prefer to not use it. Then you can end up with air problems, excess moisture, mildew, etc. And the expense of replacing a fan is tough to swallow.

The Fantech 230-3 is about $180-200, that's for the fan and the two vent asemblies.

For remote fans, Panasonic does have the FV-20NLF1, it's comparable to the Fantech 230 in regards to how much air it moves. It's a 240cfm with no load, which means it should be around 200cfm at .4, and cost wise it's probably around $130-$150 for the fan, then you'd need the two grids to go in your ceiling. Total cost for the fan and two grids might be slightly more expensive than the Fantech, which includes everything. But I do have to say that when it comes to large fans, I'm more familiar with Fantech than Panny.

Conclusion? Either the Fantch 230-2 or the Panny 20NLF1 will, even when "derated", move enough air to vent your bathroom using two ceiling vents. Both are remote, so they will both be quiet if properly installed.

If you decide to go with two individual, fully contained ceiling vents, each with their own fan, then make sure they are properly sized for the mount of ducting they will have to push the air through. Size the one in the shower for the size of the shower. Size the one in the bath for the size of the bath.

I've never had to replace a Fantech for being noisy. I've replaced a couple of Panny's for noise, but never a "whisper" series, although I did have to redo the ducting of a Panny whisper because the installer had a coupe of bends that mad too much air noise. After I tweaked things it ran quieter. I've replaced several Nutones due to noise.

All my opinion. Your mileage may vary.

Mongo

Mongo, great advice but are you saying the Nutone remote In line fans are not worthy??
I have a twin grill Nutune ILF360 used in my master bath on a timer and love it. It is so quiet I have to look up at the vents to see the dampers open to know if it is on. One vent is located in the head chamber and one just above the shower door high on the vaulted ceiling. The fan unit is mounted on the rafters in the attic.

I think it was a ILF360 cfm unit but might be wrong.
http://www.ventingdirect.com/mediaBase/specifications/ILF360spec.pdf

I am just wondering what size your bathroom is since you have a 360cfm fan? -Susan