To calculate the CFM for a fuel oil furnace, use the following formula:
CFM = ((Btu/gal oil) × (Nozzle size GPH) × (combustion/thermal efficiency)) / (1.08 × ΔT)
Where:
Use the form above to input the values, and the calculator will provide the required CFM.
https://trutechtools.com/Measuring-Airflow-using-the-Temperature-Rise-Method_c_255.html