While a few small cars being sold in U.S. showrooms get 40 or more miles to the gallon, the vast majority of 2001 model year vehicles get about 20 mpg, according to annual fuel economy statistics released yesterday by the U.S. EPA. The popularity of SUVs, pickup trucks, and minivans drove down the mileage figures. Just like the previous year, the two most fuel-efficient cars being sold in the country are hybrid gas-electric vehicles — the Honda Insight and Toyota Prius. Speaking of efficiency, the U.S. Department of Energy today will propose new standards for central air conditioners and heat pumps that would require them to use 20 percent to 30 percent less electricity. The proposal is part of a broader plan by the DOE that also aims to increase the efficiency of refrigerators, clothes dryers, water heaters, and fluorescent lamps. The DOE estimates that in 2010, its new set of standards would save enough energy to light every American home for nearly two years.