4. Cooling System
In 1980, 27 percent of homes in the United States had central air conditioning; in 2001, that number jumped to 55 percent. Air conditioning, which typically uses high-watt machines for extended periods of time, accounts for a big chunk of residential energy use. As usual, the actual number of watts consumed in cooling a home varies greatly depending on the type of unit, the capacity, the time it’s operating and the efficiency rating.