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Old 05-04-2009, 03:12 PM   #1
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Exhaust fan for multiple baths


I am remodeling an old 2 story house, and am installing 4 baths, 2 up and 2 down, 2 above the other 2. I want to install only 1 fan for all 4 baths, in the attic. Is this practical? If so, what size fan and motor should I look for? I'm thinking of venting it thru the roof, before I have the roof redone.

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Old 05-04-2009, 03:50 PM   #2
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Exhaust fan for multiple baths


"1.) First find the volume of the bathroom[s]. Volume = length x width x height
2.) Find the CFM (cubic feet per minute). Volume / 7.5
3.) This CFM is the minimum airflow required to achieve 8 air exchanges per hour.

Example: Volume = 10 x 6 x 8 = 480
CFM = 480/7.5 = 64
In this example you would only purchase a fan that has a CFM listed on the box greater than 64."

Ductwork/fitting losses may be significant for this application and if you really want to do it right you need the fan curve.


Last edited by Yoyizit; 05-04-2009 at 03:53 PM.
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Old 05-04-2009, 05:26 PM   #3
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Exhaust fan for multiple baths


Min intermitant bathroom exhaust rate is 50CFM.

4 bathrooms, means you would need a fan capable of 200CFM.
Cost you more to reheat the fresh air, then you sane on fan cost.
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Old 05-04-2009, 06:29 PM   #4
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Exhaust fan for multiple baths


And you can depressurize the house/downdraft the chimney and get CO poisoning. Would need a make up air inlet and that wastes LOTS of energy $$. I removed my central fan and replaced it with an HRV.
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Old 05-04-2009, 06:46 PM   #5
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Exhaust fan for multiple baths


Quote:
Originally Posted by orbullock View Post
I am remodeling an old 2 story house, and am installing 4 baths, 2 up and 2 down, 2 above the other 2. I want to install only 1 fan for all 4 baths, in the attic. Is this practical? If so, what size fan and motor should I look for? I'm thinking of venting it thru the roof, before I have the roof redone.
I guess you should price out all the options in view of the cautions. I s'pose you'd also need to balance the bathroom vents with dampers, just like a miniature HVAC duct system.
And buy a digital readout CO detector.
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Old 05-04-2009, 06:54 PM   #6
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Exhaust fan for multiple baths


Where are you located?
Arround here you don't want a lot of air being sucked out of the house in the winter
And in some areas the same is true in the summer - as you will be pulling in hot humid air
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Old 05-04-2009, 07:48 PM   #7
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Exhaust fan for multiple baths


Thanks a million for the input! It will probably more practical for me to put individual fans in each bath! I can make the vent pipes of the 2 downstairs baths to share an exterior exhaust vent through the outside wall, which is frame, with vinyl siding. The upstairs vents can go into the attic, and share an exhaust vent thru the roof.
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Old 05-04-2009, 08:00 PM   #8
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Exhaust fan for multiple baths


If they "share" a vent to the outside then it is possible for one bathrooms fan to push air into the other bathroom

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