How To Size An Attic Exhaust Fan

A whole house fan sucks warm house.

How to size an attic exhaust fan.

Minimum intake air vent size cfm 300 sq ft. 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. Ventilation rate of 10 air changes per hour. 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.

How to size a whole house attic fan. For the exhaust to work properly the attic should have enough intake air vents. If your attic requires a 1500 cfm fan then it should also have a 1500 300 5 sq ft air vent. Intake air vent size.

Use the chart below as an attic vent fan cfm calculator. A whole house attic fan is installed in the ceiling between the top floor and the attic as a supplement to air conditioning. So here the cfm of the fan cfm x 1 15. Enter the length and width of your attic or ceiling crawl space.

For open blade fans see our ceiling fan calculator. Your attic fan should be sized to the square footage of your attic. Set the thermostat on your attic vent fan so that it cuts on between 100 and 110 f. Select if your roof is more flat of peaked.

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. Humidity sensors are also available that cut the fan on if moisture in the attic becomes too high. For heating and air conditioning airflow or for other exhaust fan situations see our airflow calculator. Attic fan size chart for quick reference.