One of the main issues we see time after time, is homes with improper sizing with regards to ductwork, particularly on the return side. This creates all kinds of airflow problems, with some areas being too hot, others too cool. Ductwork is very much ignored in our industry, unfortunately. We look at your ENTIRE HVAC system as a whole, analyzing the building envelope. DO NOT put your HVAC system in the hands of ANYONE who refuses to analyze your duct system, and perform a duct system test to ensure static pressures are where they need to be.