10. High-efficiency water heaters: These can drive down home energy costs as well. "Water heating makes up anywhere from 15 to 25 percent of the annual energy usage in a home," says Steve Koep of Marathon Water Heaters. High-efficiency water heaters conserve energy by keeping water hot for longer than traditional water heaters. "You start saving money on a monthly basis, and that technology will generally pay for itself in anywhere from three to five years," Koep says. Certain water heaters can qualify for federal tax credits.