So I'm really guessing that the system is slightly oversized. I also need to mention that the XR15 has a loud start up outside. The installers who installed our upstairs unit a few weeks ago said the XR15 might need a hard start kit. To add more information, we have 4 return branches connected to the ductboard. Two of them are 10", one is 12", and one is 6". We plan to call a tech out to look at everything including the ductwork. But for now, what are your opinions?