Outside air calculator
Enter the design info, pick a method, and enter the readings. Traverse ducted outside air whenever you can; these methods are for when you can't. Nothing is saved on this page.
Design info
Method
Balance supply first and set the fan for full airflow. Close the OA damper, open the return damper, and read return SP. Then open the OA damper and read return SP again. Supply SP must not change, or the total CFM changed.
Use when outdoor air is at least 20 °F warmer or cooler than return air. Take averaged readings; don't read mixed air right at the OA damper.