The existing system was a 5 ton Rheem and was changed-out with the model that was specified as the replacement by Rheem. We did not calculate the ductwork, we didn't think we had to. They come off with a plenum that is 21"x21"x24" and run flex from there out. The flex drops only account for 1300 cfm and the supply plenum, if you want to call it that should extend out further, at least 8' in my opinion.They might have had that same problem I don't know, we were brought in to change the system and were unaware of previous problems with the old system. I have asked for a report from these other companies she supposedly hired and have yet to recieve a response. I even offered to pay for any legitimate repairs that involved the actual system and not the ductwork, with right to inspect.