Probably because there are no requirements as far as HVAC companies go. This is an engineering problem and beyond the scope of all but the big ones that also do their own engineering.
By engineering I mean a professional with a stamp.
Most larger jobs are off a set of prints that have been engineered. Some smaller ones too.
But your idea of a forum is a good one. Sometimes posts will show up here from time to time that ask these types of questions and will get few answers. Some here are engineers but most are techs or tradesmen.
I should have played the g'tar on the MTV. MK
You can be anything you want......As long as you don't suck at it.