Calculate the amount of air exchange needed (Volume) in order to adequately ventilate the area.
CFM (Per Fan)
To calculate the Volume required to adequately ventilate an area, we divide the room volume by the appropriate "Minutes per Change" value.
[Volume] = [Room Volume] / [Min./Chg.]
Step One: Determine Room Volume
Step Two: Determine Minutes per Change
Number of Fans:
Calculate the amount of static pressure the fan must overcome..
The pressure generated by fans in ductwork is typically very small. An accurate measurement of static presure is critical to proper fan selection however. Static pressure in fan systems is typically less than
2'' SP, or 0.072 Psi.
The amount of static pressure that the fan must overcome depends on the air velocity in the ductwork, the number of duct turns (and other resistive elements), and the duct length. For properly designed systems with sufficient make-up air, the guidelines in the table below can be used for estimateing static pressure.
Step One: Total Pressure Due to Ductwork
Step Two: Pressure From Fittings and Other Resistive Elements
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