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 Three: Number of Fans:

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 498.2 Pa 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.