Heating and cooling account for 40 to 50 percent of your home's energy use. And electricity prices? They jumped 6.9 percent in the past year alone. But here's the part nobody tells you: you don't need a new furnace to fix it. In fact, one of the most powerful tools for lowering your bill is already on your wall. The Department of Energy says for every single degree you lower your thermostat during heating season, you save 1 to 3 percent on your bill. Set it back 7 degrees while you're at work? That's up to 10 percent—without spending a dime.