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Is 0.0 the appropriate external static pressure to use when sizing a high flow exhaust fan that is not ducted on either the inlet or outlet? I can't find any specific guidance on this practice, yet I'm reluctant to assume 0.0 due to friction losses. On the other hand, I can't think what values to use to even begin trying to quantify the pressure.

Secundus
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  • I'm assuming it's gauge pressure; not absolute? – JMac May 09 '17 at 12:39
  • Depends a bit on the definition of "ducted." I'm thinking of whole-house attic fans, which will not function properly if there's insufficient venting in the attic. Not strictly a duct, but there is back-pressure. – Carl Witthoft May 09 '17 at 13:28
  • Add a picture please. – MrYouMath May 09 '17 at 20:23
  • A picture would help here x2. Assuming the exhaust outflow is into open air, your static gauge pressure would be 0. You also are going to need the flow rate (and piping geometry) to quantify pressure losses. – phyllis diller May 10 '17 at 16:59

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