I have a background in mechanical engineering but HVAC is not my specialization. I am trying to properly size an axial fan to get a determined airflow from a duct. Both inlet and outlet are at atmospheric pressure. You can see in the diagram that it is a very simple system with 1 inlet and 1 outlet. I have a main filter at the inlet with the given pressure drop at the CFM i am trying to achieve. I also have a secondary filter with much lower pressure drop. Assuming a laminar flow condition and negligible pressure losses in the duct (I can check these assumptions on my own), what would be the way to determine the required pressure from the fan to achieve the desired CFM output?