My contractor just completed installing my new system. Trane XV95, XB13, T803, and all new ductwork. Part of the system serves a new addition (780sft). The addition is not yet insulated and drywalled so all the registers and returns are closed/covered. The remainder of the system serves the existing 1040 sft house. Can/should the system be run in this condition? The contractor said it's fine because there's plenty of return air in the existing house.