"I am not one of those guys with a lot of letters behind my name. All of what you are about to read are my own thoughts on the subject based on my thirty years of experience in the field of HVAC distribution and you are getting exactly what you are paying for. I have to generalize a bit so your particular HVAC system may not be described in full – the universe is simply too large. Even if you follow this advice, you still might get covid. Forward."