Getting in the habit of turning off lights, unplugging appliances when not in use, and upgrading to LED light bulbs can all help. But for really big savings, look at your home’s heating and cooling systems: upgrading to high-efficiency models can dramatically increase energy efficiency, with heating AFUE ratings going from 56-70% for old models to 95% with new furnaces, and air conditioners going from a SEER rating of 13 for older models to 18 or higher. Installing a smart thermostat is another way to save money on energy bills, regardless of system age or efficiency.