Depending on where you live and the size of the unit, a properly sized and installed ENERGY STAR furnace will use about 20% less energy than a standard furnace. Furnaces are the most commonly-used residential heating system in the U.S.
Furnaces that have earned the ENERGY STAR meet strict energy efficiency criteria, and help save energy and money without sacrificing performance.
Consider replacing an existing heating system if it is older than 10 years, and make sure your unit is properly sized and installed to maximize the unit's efficiency and your building's comfort.
U.S. Department of the Interior
Greening of the Interior