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Posted by Red Green on May 6, 2008, 10:12 pm
> Joseph Meehan wrote:
>>> I am trying to size my bathroom exhaust fan. Most sizing chart says
>>> to use the SQFT size and multiply by 1.1 to get the CFM if ceiling
>>> is standard 8'. So for a 10x10 bath = 100 SF it would be 110 CFM.
>>>
>>> However when you use finish using your bath typically you have the
>>> fan on and the bathroom door open right? So it's drawing the air in
>>> the bath PLUS the air from outside the bath. Would it be a good
>>> rule of thumb to overshoot the 1.1 multiplier? or that already have
>>> a safety factor built-in?
>>>
>>> Thanks,
>>>
>>> MC
>>
>> No additional factoring needed. They are measuring room air
>> changes
>> per time. The make up air will come from somewhere like the heat
>> vent, open door or window etc.
>>
>> Basically physics says you can't draw air out of the room with out
>> air coming into the room at the same time, even with the door closed
>> air has to come in from somewhere (like around the door or cold air
>> return).
>>
>>
>
> Many bathroom doors are cut a little short on the bottom to let air
> into the room just because of exhaust fans.
>
> Lou
As far as I know, all interior doors should have a 1/2-3/4" gap on the
bottom for air circulation if you have forced air HVAC.
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