Bath room fan CFM ratings

I did the usual CFM calculation for my bathroom and came up with 68 CFM. So anything rated 68 CFM and above would work. I've been looking at 80 CFM fans and also 100 CFM fans. If I go with a 100 CFM fan (or even 110) would that be too powerful for my small bathroom or it doesn't matter?
Thanks, Walter
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Walter Cohen wrote:

Hi, Trying to suck out all the warm air? Like cold bahroom?
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Skip the cheap NuTone and get a 120 cfm Panasonic. Much quieter. I don't know how you did the calculations, but the amount of methane gas you produce should be considered above anything else.
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somebody who needs 100+CFM should also get something with a spark arrester.
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wrote:

What about moisture? Unless you are living in an arid climate, fighting bathroom mold and mildew is no fun. Expect to pay 30% more for a "quiet" fan with the same CFM.
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Broan makes a 70CFM. Keep in mind noise also becomes a factor the larger CFM you get, unless you ante up and buy the quiet models. What size is your bathroom?
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its probably more important to have a air intake to the room so air can flow, perhaps a louver in the door or some such.
otherwise the room is sucked to a vacuumn and the blower is ineffective.
you can also install a fan thats at a remote location, like the point where the air exits the home.
much quieter that way
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On Wed, 6 Feb 2008 05:16:31 -0800 (PST), " snipped-for-privacy@aol.com"

Most bathroom doors have enough gap at the bottom.
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not in the homes i have visited
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On Tue, 5 Feb 2008 21:57:02 -0500, "Walter Cohen"

Generally, the higher the CFM the more noise. If noise is not an issue, go with the higher CFM. A wall timer for the fan circuit is a good thing too.
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There's ALMOST no such thing as too big a fan, especially if noise is not an issue. How many people take showers, and in what period of time?
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JoeSpareBedroom wrote:

I think there are some possible issues with the backflow of combustion gases from furances or hot water heaters with an overly aggressive exhaust fan.
My guess is you need the right other ingredients (very tight house, minimal or no fresh air intake, gas hot water heater & furnace, strong fan and limited loss exhaust duct) for this to be a significant issue, but I've heard it mentioned more than once.
My personal experience has been that most insulated flexible exhaust ducting of any length is so grossly inefficient that you almost need a high CFM fan for it to be effective at all.
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Well, I plan on using standard 4" round rigid exhaust ducting (aluminum) vented through the roof, not the outside wall.
Walter

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Walter Cohen wrote:

If you live in a cold climate, make sure to insulate the ducting as warm air rushing through the ducting can lead to condensation problems in uninsulated space the duct runs through.
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outside wall is better the fewer the roof penetrations the better
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Also, when I mount the fan housing to the ceiling joist should I make use of rubber stand-offs (washers) between the joist and the housing (to eliminate any vibration/noise (in case there is any) against the wood joist?
Walter

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