How To Size An Attic Exhaust Fan

Select if your roof is more flat of peaked.

How to size an attic exhaust fan.

For heating and air conditioning airflow or for other exhaust fan situations see our airflow calculator. Ridge vents it s not a good idea to use a power vent fan if your house has a ridge vent since the fan will tend to draw in air from the ridge. Your attic fan should be sized to the square footage of your attic. Attic fan size chart for quick reference.

Use the chart below as an attic vent fan cfm calculator. For the exhaust to work properly the attic should have enough intake air vents. Minimum intake air vent size cfm 300 sq ft. For open blade fans see our ceiling fan calculator.

Intake air vent size. How to size a whole house attic fan. Enter the length and width of your attic or ceiling crawl space. For example a 1 000 square foot attic needs to have a fan that can handle at least 460 cubic feet per minute of airflow.

If your attic is poorly insulated or you have problems with excessive moisture you may need a larger fan to help account for the additional heat. Humidity sensors are also available that cut the fan on if moisture in the attic becomes too high. Then click on calculate. Then enter the height at the highest point.

If your attic requires a 1500 cfm fan then it should also have a 1500 300 5 sq ft air vent. A whole house fan sucks warm house. Set the thermostat on your attic vent fan so that it cuts on between 100 and 110 f. Ventilation rate of 10 air changes per hour.