There’s been a lot of emphasis lately on making houses that are more energy efficient — with better insulation and windows that seal out heat and cold. Many feature the use of solar panels to capture the natural heat of the sun. The first house in America with solar heating and radiation cooling opened this week in 1955 in Tucson, Arizona. A large, slanting slab of steel and glass converted sunlight into heat, which was ducted into the house. In America’s 115 million occupied housing units, gas remains the most common heating fuel, outpacing electricity — 54 percent to 36 percent. All other types of fuel are used in just under 9 percent of U.S. homes. You can find more facts about America’s people, places and economy, from the American Community Survey, at <www.census.gov>.