When mounted in this way, it is similar to a large window fan. Attic fans mounted as in Figure 5 can be used to cool the attic to reduce the load on an air conditioning unit. When used for this purpose, the fan is operated only during the day to keep the attic temperature from building up. Thermostatically controlled switches are available to control fan operation automatically. Do not install a fan in the attic, as in Figure 5, to cool the house.
Attics have many cracks and places for air to leak through.
The fan will pull air through these cracks and will do a poor job of ventilating the house. Size of intake and exhaust openings These openings should have at least one square foot of open area for each 1,000 CFM fan capacity. If openings are covered, use values given in Table 2. Copyright 1999 University of Missouri. Published by University Extension , University of Missouri-Columbia.