APPENDIX C (continued)
WHOLE-HOUSE FAN SIZING PROCEDURE
Assumptions. Whole-house fans should be sized by assuming that 30
to 60 air changes per hour (about 0.5 to 1.0 per minute) are to be provided to
the building depending on the severity of the climate.
Minimum Required Airflow, CFM.
Calculate the minimum required cfm
using Equation 31.
CFM = 0.5 x building volume
volume = ft2 * ceiling height
Fan Selection. Select a whole-house fan which has a cfm rating
equal to or greater than that calculated above. Note that this should be the
whole-house fan cfm rating at 0.1-inch water static pressure (SP) drop and not
the free air cfm without any pressure drop. If the cfm rating does not state
the pressure drop, assume it is for free air. For fan selection, derate the
free air cfm by 25 percent to get the 0.1-inch SP rating.