How To Size An Attic Exhaust Fan

Then enter the height at the highest point.

How to size an attic exhaust fan.

Enter the length and width of your attic or ceiling crawl space. Set the thermostat on your attic vent fan so that it cuts on between 100 and 110 f. Attic fan size chart for quick reference. Your attic fan should be sized to the square footage of your attic.

If your attic requires a 1500 cfm fan then it should also have a 1500 300 5 sq ft air vent. Select if your roof is more flat of peaked. 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.

For heating and air conditioning airflow or for other exhaust fan situations see our airflow calculator. Minimum intake air vent size cfm 300 sq ft. Proceed to step 2 and use the chart to determine the size and number of solar powered attic ventilation fans required to achieve a min. For open blade fans see our ceiling fan calculator.

Humidity sensors are also available that cut the fan on if moisture in the attic becomes too high. 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. For the exhaust to work properly the attic should have enough intake air vents. How to size a whole house attic fan.

Use the chart below as an attic vent fan cfm calculator. 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. Then click on calculate. So here the cfm of the fan cfm x 1 15.