its a common enough install in my area. not lots of folks vent thru the roof.
some things to be aware of:
cut in sheetrock being oversized so that there are
gaps between sheetrock opening and the housing of the
bath fan.
I use mastic tape to seal these gaps as they let
not only attic temps but the insulation particles into the house.

back draft damper..only 2 ways you can install it.
1 where damper is closed when fan is off.
2 where damper is open when fan is off.
#1 is the correct way, but I often turn the back draft
damper around on installs where they used method 2.

This damper should be attached with my favorite
hardcast brand mastic tape #1402. this same tape will
seal the gap at the sheetrock to the housing of the bath fan also.

then the venting. if the fan is installed where the back draft damper faces the soffit rather than where it faces into the attic, then venting will make a straight run to soffits, this is what you want. if the fan is installed the othe way the venting will have to make a 90 degree turn to get to the soffit.
this will cause air flow issues.

there are different types of venting. the dampers are the same size as a dryer vent, so with dryer vent there are the cheap plastic white vents that dry out quickly and split. don't use that one!
there are the flex silver dryer vents that are flexible.
and rigid dryer venting.
I usually use the flex silver venting, and you got it
mastic tape it to the damper, then mastic tape the damper to the fan and then vent through soffit.
there are covers that cover the venting thru the soffit.

make sure that your back draft damper is correctly installed, I've picked many of them up off the trash plies
after electrician doesn't install them. Take a look at his work during the install.

quiteness is always an issue. bath fans are rated in
sones, the lower the sones the quiter the fan.

thats my .02!
have a good one.

If you live in a cold climate, then I suggest the vent in the attic is insulated in order to prevent condensation.

I also suggest adding a timer. I like the electronic push button type.

mike -- Don't know that we will need a timer. It's just DH and I -- retired -- can remember to turn it off, I think. BTW, how long should it run after a bath or shower?

energy rater -- The specs say the backdraft damper is within the 8" duct connection portion of the fan, not whether it faces in or out. I need to ask that they face it away from the fan itself, right? Or are you saying the damper should be not at the fan, but at the soffit?

The bath is on the NW corner of the house. Air and moisture will go UP through the bathroom ceiling into the fan, ACROSS about ten feet of attic floor, then out a West soffit. Is it at the soffit that you want metal-flex flaps? Does moisture acclumlate there? Drip outside the exterior wall? (Yeah, where DOES the water go?)

I see round aluminum-looking flex-ducting in the attic. Is that what I should expect to see on this install -- not hard metal ducting like a forced air furnace?

Is this capacity appropriate? I want to eliminate excess moisture, but don't want to be taking baths or showers in a wind tunnel! (It is meant to run *while* one bathes and a short while afterwards, right?)

Is a sone rating of 1.7 good? Is Broan a good brand?

This installer is also going to correct three other, smaller bathroom exhaust fan ducts that now empty INTO the attic instead of outdoors. Price is $900 all in for Broan unit and all work. He says it will take about four hours. We are north of Chicago in a high-*address tax*-suburb, as my DH terms it.

Thanks so much for your time and trouble. Much appreciated. I'm probably overly concerned, but we keep finding faults (like these fan exhausts) in a house that passed city inspection when it was built only 10 years ago. I'm sure it was not code to vent into an attic!

I turn the fan on before I start my shower. I will usually set the timer for 20 or 30 minutes. There is no set period of time. If you are good about turning it on and off, then the timer is not required.

I personally like the Panasonic bathroom fans. There are several models some of which have built in lights and heaters. I would not get overly concerned about the sound rating. The sound of the running water drowns out most of the sound.

Maybe this link will help.
look at the fans and the plastic damper that attaches to it.

http://broan.com/display/router.asp?CategoryID=100355

the back draft damper it the plastic piece attached to the
housing of the fan.

the fan's damper should point at the eaves where it will be vented out of the attic space.
if it is installed where the damper does not face the
eaves (soffit) the venting will have to make a 90 degree
bend to reach eaves to be vented through.

the damper is a square to round plastic piece.
the square end connects to the housing of the bath fan
the round end is where the venting connection is made.
both should not be installed with duct tape.
The damper itself is within the damper. what is of
import is that it is installed in a position so that
it remains closed when not in use.

8" damper is bigger than I have seen. In my hot humid climate it is normally 4" ocassionally 5".
check the install directions that come with your product.
larger than 4" you may need to use insulated flex duct.
It depends upon the mfg specs, location of your home
and cfm output of the fan.

best of luck

OK, I *think* I get the sequence for what goes where; no 'duct tape';, damper closed when fan not in use.

Please look at my more basic questions too. Is a Broan L200 appropriate for a 12 X 14 X 12-high bathroom? Are 1.7 sones going to be pretty loud? Will it be drafty with this running? (Remember, I'm sitting in a tub 11 feet lower and directly under it.)

We have under-tile floor heat and some forced-air central heat in this bathroom. It's OK temperature-wise NOW; don't want a drafty bath -- just want the moisture out.

You can see this model from energy's link to Broan: L200. BTW, I don't need a heater or a light; would Panasonic be superior? I'd heard that Panasonic is of lower quality now that it is made in Korea.

You have a big bathroom with a high ceiling, I doubt you will feel any draft even with a fan pushing 210 CFM.

This is a big fan, it is not going to be silent. If you want a quieter fan than look at the Panasonic FV20vq3. It is rated at 1.3 sones and 190 CFM.

The Panasonic fans have been made in China for a long time. Who told you they are made in Korea? Do a search in the Bathrooms forum. You will find Panasonic fans are very popular.

Thanks, Mike. I'll ask the electrician about Panasonic fans.

I assumed everything Panasonic was being made in Korea because I was told that about Panasonic air conditioners.

We have a 10-year-old Panasonic through-the-wall in a condo on Maui that's still working fine. When we put another Panasonic in another room there four years ago the supplier said the brand had slipped because it was now being manufactured in Korea, not Japan. It failed this year.

Thanks for your help and patience.

Panasonic makes a Whisper Quiet fan
something like .8 sones.
best of luck

I put in 2 Panasonic fans and I need to put them on a timer because they are so quiet you can hardly hear them. I have 2 small baths and went one third higher on the cfm's and I still get a small amount of condensation but it clears quickly. I put an elbow directly off the fan exaust and went straight up approxamatly 3 feet with insulated duct. Then I went through the roof with roof caps. I am not sure if the elbow dirtly off the fan exaust is the optimon was to go. Maybe someone can chine in.

If you are going to vent through the roof, then you will need to have at least one elbow. Is this a hard elbox, or did you connect the duct directy to the fan port?

If you connect the duct to the fan, you have the ability to make the radius of the elbow larger. This will allow better air flow. I don't think you have be overly concerned about this. I doubt it will make a significant difference on the air flow.

Below is a link to calculate the amout of air flow you need based on the size of the bathroom. The numbers are based on general guidelines. It is not a big issue to have a fan which is a little bigger or smaller than the calculator estimates.

http://www2.panasonic.com/webapp/wcs/stores/servlet/vCeilingContinuousFan?storeId=15001

Hey Mike....the elbow is hard duct chanped and taped on both ends and covered with insulation. I purposly closed the bath door and showered with the fan on. The space is only 8x10. I had some steam on the mirrow and the top of the walls but it cleared in minutes. Thanks for the reply