Dumb question, but when we had our home inspected by a home inspection firm(we were about to sell our home) he said we could never have central air with the existing furnace we had because it wasnt a high efficiency furnace. Is this true? So we would have to get a new furnace as well? Also, do you need to have cold air returns in every room in order to have central air? One bedroom does not have one! Is it cheaper to just get a new furnace and central air at the same time?