Sizing ductwork correctly is one of the most crucial parts of having a HVAC system work. I wish every contractor would study the manual D guide, but I know in real life, most just don't have the time, so a shortcut to get sizing at least close is better than just outright guessing, so thats where this video starts. I'm adding links below to a static pressure video and calculating ductwork using manual D.

Related videos:
1.) Static Pressure Testing P1:
   • Tech Tips: Static Pressure Testing  
Static Pressure Testing P2:
   • Tech Tips: Static Pressure Testing Pa...  
2.) Duct Calculation using manual D:
   • Air Duct Calculation explained