I have a four bedroom ranch home about 50 years old. My question: am I saving money by closing the air vents in 3 of the bedrooms, living room and dining to save on A.C. costs? I have French doors between the living / dining room and den / kitchen, so closing off rooms is very easy. 95% percent of my time is spent in the den, kitchen and one bedroom. The main return air duct is in the hallway. Am I saving money by closing off as many rooms as possible or better to leave one or two more rooms open? Appreciate your thoughts !!