Hi! I have central air upstairs only that we just installed this week. Our house is so large that we're trying to do it in installments. The upstairs this year with a low-velocity system and then we will install two Mitsubishi systems next year for the downstairs. We have 4 bedrooms that are air-conditioned as well as the attic playroom and the large return is in the hallway as well as the thermostat. Should we keep the bedroom doors open or closed? My husband thinks that we should keep the doors closed or the system will continually run costing us a lot of money. I think that the doors should be open to allow the air to circulate better to put less stress on the system. What is the right answer?

The only way closing doors works is to also close the supply and return vents for the room. Just closing the door may save a few cents but throws off all the other rooms, particularly since you have a central return.