Pew FactTank: “U.S. homes have become considerably more energy-efficient over the past four decades, according to government data. But homes also are a lot bigger than they used to be, and their growing girth wipes out nearly all the efficiency gains. According to preliminary figures from the Department of Energy’s Office of Energy Efficiency and Renewable Energy, the average U.S. home used 101,800 British thermal units (Btu) of energy per square foot in 2012, the most recent year with available data. That’s 31% less than in 1970, after adjusting for weather effects and efficiency improvements in electricity generation.”