The practice of closing off vents in parts of your home that aren’t being used in order to save money dates back to when homes were heated from a central location, like a fireplace.  Back then it worked.  Today homes are equipped with central heating and air conditioning systems, by closing off the parts of your home and shutting vents in those areas, you can actually increase your energy costs, not reduce then.  The reason is simple; a modern home’s HVAC system is designed to either heat or cool the entire residence, and is sized according to this need.  By shutting off a part of the air flow, you increase the air press on the system, which can increase the amount of leakage from the ductwork.  In fact, too many vents closed can actually cause your HVAC system to malfunction.  This is because today’s systems rely on a certain amount of air flow to maintain a certain temperature within them.