max power for a bathroom fan?

I have a little bathroom, I want to have the most powerful fan in there that I can, without obviously overdoing it - like having a lot of wind in there! I'd put an inline fan in the attic. I'm not sure how much would be too much. I'd like it to double as house ventilation, to empty the hot air out of my house overnight, that's why I want a fan more powerful than the minimum.
If you have a powerful bathroom fan, and it's too powerful, can you tell me its CFM and what the square footage of your bathroom is?
Or, if you have a powerful bathroom fan, and it's NOT too powerful, same thing? So I can get a ballpark idea of how much power is too much.
I could put a variable speed control on the fan, Fantech's inline fans take a variable speed control that goes from 0-100% - so I could put in a bathroom fan that's too powerful for the bathroom, and use it dialed down when it's being used just for bathroom ventilation. I guess - I don't know if there are hitches in that idea.
Thanks. Laura
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If you try to use the bath fan for whole house ventilation, you will have a problem in the winter when you want to get rid of steam and smell cause the window is closed and you end up exhausting all that air in the rest of the house you just paid to heat up.
I think a timer and thermostat would result in more efficiency than a thermostatic control only. Consider the thermal mass of the house and contents. If you wait for a thermostat to demand the fan, the whole house will be hot when it comes on and it will take longer to cool as the furnature and walls are hot as well as the air.
With a timer, you can set it to run into the evening pulling in cool night air and cooling the contents, then turn it off in the morning to keep that cool ari inside as the air outside warms up, then at the right time, turn the fan on to prevent the inside air from warming above the outside air temp

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PipeDown wrote:

I agree with Pipedown. I doubt a bath fan in a small bathroom can be practical and serve as both a bath fan and also a whole house fan. To move air through the entire house requires an order of magnitude more air flow than a bath fan. One properly sized for one use isn't going to be much good at all at the other.
As for bathroom fan capacity, the ballpark estimate for small to med size bathrooms is 1 CFM for every sq ft of floor space.
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Lacustral wrote:

Laura-
Bathroom fans serve the purpose of odor & mositure control. The suggestion of 1 CFM per square foot of bathroom area is a good one.
Sizing an attic fan / whole house ventilator uses the same rule of thumb but results is a whole different animal!
Even a small house (1500 sq ft) would suggest a 12,000 CFM fan .........about 100 times the capacity of the fan for a large bathroom.
I have "cheated" & used a 20" box fan jammed in a window as a "poor man's" whole house fan......not the "correct" solution but if you get good night time temperature drop where you live, it will do the job and cost peanuts.
A 20" box has about 2000 cfm......now you're only off by a factor of 6 or so not 100! Use two 20" fans & your even closer.
cheers Bob
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"Hello. I am your small house. I suggest a 12,000 CFM fan."
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Nick-
I'll bet you crack yourself up.
cheers Bob
BTW both small houses were wrong with their suggestions : :)
a whole house fan for a 1500 sq ft house sound have ~ 4500 CFM capacity
which is apporx 20 air changes per hour
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Well, he cracked -me- up completely! Thanks!
Bonita
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snipped-for-privacy@adore.lightlink.com (Lacustral) wrote:

I installed Panasonic fans in my baths, at ~150cfm they are meant for much larger baths, but are quiet enough not to be objectionable. With an approx bath size of 500cu ft, that is a turnover of once every 3-4 minutes.
I wear eyeglasses, and now I can see when I get out of the shower, since the glasses don't get fogged up, so it works great.
-- If I had something witty to say, this is where I'd say it.
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