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Attic Fan Ventilation Calculator

This calculator requires the use of Javascript enabled and capable browsers. This calculator is designed to arrive at a reasonable attic or ceiling crawl space ventilation fan air volume displacement rating for minimum, normal and optimum outside heat conditions. This vent fan removes heated air from inside that space and should be placed near the peak to effectively remove the hottest air. The extreme conditions might be considered the normal use in extreme high heat areas. Enter the length and width of your attic or ceiling crawl space. Then enter the height at the highest point. Select if your roof is more flat of peaked. Then click on Calculate. For heating and air conditioning airflow, or for other exhaust fan situations, see our Airflow Calculator. For open blade fans, see our Ceiling Fan Calculator.

Required Data Entry
Height Feet
Width Feet
Length Feet
Roof Type

Calculated Results
Minimum Conditions Ventilation Fan Rating CFM
Normal Conditions Ventilation Fan Rating CFM
Extreme Conditions Ventilation Fan Rating CFM
Version 1.4.5

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