I'm not familiar with the history of ASHRAE but it seems like the older versions were well below a 4+ air change rate, in addition to other serious issues[1]. T

I'm not familiar with the history of ASHRAE but it seems like the older versions were well below a 4+ air change rate, in addition to other serious issues[1]. The the most stringent spec as of 1999 for a 1000ft2 classroom with 30 people had a required supply airflow of 450 cfm which gives you only a theoretical 2.7 ACH assuming 10ft ceilings and perfect air distribution. The CDC targets are just a suggestion at this point but they are likely just the first step in retrofitting existing buildings. [1] Ventilation Through The Years: A Perspective https://www.aivc.org/sites/default/files/airbase_12483.pdf https://www.aivc.org/sites/default/files/airbase_12483.pdf