I put my own system in and it has been running nicely. I have to add a second return on my second floor because the unit originally did both floors and had a second return downstairs. It also will be shy of the 400cfm per ton if I dont. For my new unit I was thinking about adding a second return to the living room because my air flow calculations put the existing return at just bairly enough airflow. I was reading today where some contractors have started putting returns in every room. This of course would be minus kitchens, bathrooms, closets, and small rooms. I was thinking living room, family room, and each bedroom. I know my bedroom now will get stuffy with the door closed and two people plus a dog sleeping in there all night. Is there any downside to this besides the need for either a central filter or a filter on each box? Does anyone have this setup and like it?