Your Home With a Window or Attic Fan Joseph M. Zulovich Department of Agricultural Engineering, University of Missouri-Columbia Window or attic fans are very effective when outside air is cooler than the temperature inside the home. Operated during the evening and night, these fans exhaust warm air and bring in fresh outside air through doors and windows. Fan size To be effective, a fan should be able to change the air in the house at least once each minute. Fans are rated by the volume of air they will exhaust per minute. Manufacturers furnish these ratings with each fan.
Large fans deliver a given amount of air more slowly than smaller fans and usually make less noise.
To determine the fan capacity you need, figure the volume of the rooms you intend to cool. Table 1 gives typical attic and ceiling fan specifications. Use this table as a guide only. Always refer to the manufacturer's ratings. Attic and ceiling fan specifications.