Common sense...doesn't exist. It is what you believe others should know, based on your years of experience. Its a myth. Nobody learns anything without asking questions and doing stuff, and that includes everybody here.
What is an EE?
I cant help but feel sorry for people who are territorial about their profession. There is nothing an HVAC tech can do that I couldn't do without the proper knowledge and equipment. You've admitted it yourself: it's a series of calculations and some book knowledge. It's basic mechanical engineering with maybe a touch of fluid dynamics. And there are those who insult people who haven't learned it yet and are stupid enough to wonder about it.
The only difference between home electrical and home HVAC, is that there aren't a bunch of DIY books on the subject. And someday that will change. Just like with all the other trades, people will hire a pro only when the job is too much to bite off. And they'll have the knowledge to properly tackle the jobs safely. No longer will we have to suffer $75 service calls just to get browbeaten.
For those who helped me, thanks! You've confirmed that my project is best left untackled. And I will get a pro to help balance the system before I finish the basement.
For those with disdain for the DIY'er... You might be better served by specializing in fixing amateur jobs. Because all your secret knowledge is being gradually pried open. There will be a day when people won't have to take abuse from guys because they happen to bend sheet metal and run calculations for a living.