Thanks Jason, I see you're thinking along the same lines as me (and your drawing is much better). However, I see three drawbacks of your design. 1. The anemometer will restrict the airflow more. 2. The anemometer will be designed expecting axial airflow, while in your design the air exiting the box ...

I've been thinking about the problem of CFM measurement and have come up with the following. It solves three problems with the current solution: positioning of anemometer, effects of turbulence and measurement of the open area of the fan. My proposed solution is a (cube shaped) box (see image) with ...