Generally, a boiler heats water that’s delivered through copper and/or plastic (PEX) pipes inside a building’s walls and floors. Popular high-efficiency boilers tend to be more expensive at installation, but lower utility bills pay you back after time. In fact, the U.S. Department of Energy estimates that replacing an older boiler system with a new, high-efficiency one can cut fuel bills in half. To protect that investment, high-efficiency boilers need some maintenance, just like your car.