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Old 05-03-2012, 08:25 AM   #1
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Bathroom Fan Size


I am installing a new fan in an existing bathroom. The bathroom is 8' x 5'. There is a bathtub, sink & toilet. No shower. I will run a 3" duct (see other thread, why) down the wall(6ft) then outside(3ft) with 2 90's or down the wall with 1 90 turn & 10 ft to outside. Using 3" ducting I don't have many fan options. Any suggestions on what size is required?
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Old 05-03-2012, 09:45 AM   #2
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Bathroom Fan Size


http://www.checkthishouse.com/3978/b...an-sizing.html

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Old 05-03-2012, 09:56 AM   #3
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Bathroom Fan Size


guidelines that recommend approximately 8 room air exchanges per hour

Maan, that's gonna be a cold bathroom! Make sure you are buying a vent with at least two speeds. Hi speed for turbo-freezing jet-like 8 exchanges per hour, and low speed for comfy silent bathing at ~3 per hour rate.
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Old 05-03-2012, 10:25 AM   #4
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Bathroom Fan Size


I guess my question basically is will a 50 CFM meet my requirements or should I use a 70 CFM. My concern with the 70 is the noise level but if a 50 is too small I can live with the noise.
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Old 05-05-2012, 11:38 PM   #5
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Bathroom Fan Size


Quote:
Originally Posted by wndnns View Post
I guess my question basically is will a 50 CFM meet my requirements or should I use a 70 CFM. My concern with the 70 is the noise level but if a 50 is too small I can live with the noise.
Thanks
Late to the party but...50 cfm should do it nicely...with 4" pipe. The static pressure will be greater when using 3" pipe. Turns in the piping also increase static pressure. As static pressure increases, cfms decrease.

I did read your other thread. Have you considered venting through the roof? Here is a flashed roof cap that will work well (I installed this very one. It's well constructed and low profile). You install the jack and seal the pipe init from the underside:

http://www.grainger.com/Grainger/BRO...905?Pid=search

If you have doubts about how well your ventilator will perform with your planned pipe size and run, call the manufacturer. Give them the details of your pipe run (i.e., length, pipe size, 90 degree turns). They'll be able to tell you what your cfm rating will be for the static pressure your pipe run will produce.
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Old 05-06-2012, 09:45 AM   #6
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Bathroom Fan Size


Thanks for the reply. I really don't want to go up in the attic or cut into my shingles at this time. So my problem is the 3 inch duct and whether 50 CFM is enough. But your advice in calling the manufacture is good advice (Broan)
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Old 05-06-2012, 11:03 AM   #7
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If I were you, I use 4" and 70cfm. I have a 6x7x 9high bath room with 3" and 50 cfm. It is too small.
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Old 05-06-2012, 11:08 AM   #8
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Bathroom Fan Size


Thanks. I will need to use the 70CFM then. As I will be using 3". 70 has been the largest 3" size that I have seen.

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