You are on the right track
the 0.5 on the furnace name plate is the design static pressure, the 0.3 on the air handler includes the evaporator coil. Most coils have around 0.2 to 0.3 that needs to be subtracted from the furnace 0.5
Originally Posted by GarnetJax
Not all gas furnaces will have a coil added to the system.
A fan curve chart is supplied showing the selected fan motor, fan cfm, and at what pressure drop, or static pressure.
Look in the educational section
for some help. Unfortunately most trade schools do not teach what students need to know.
Originally Posted by Redwood650