When a centrifugal fan is specified for a given CFM and static pressure at conditions other than standard, an air density correction factor must be applied to select the proper size fan to meet the new condition. Since air weighs only 80% of air, the centrifugal fan creates less pressure and requires less power. To get the actual pressure required at , the designer must multiply the pressure at standard conditions by an air density correction factor of 1.25 (i.e., 1.0/0.8) to get the system to operate correctly. To get the actual power at , the designer must divide the power at standard conditions by the air density correction factor.