Boilers with an ENERGY STAR label can be up to 19% more efficient than models that simply meet the U.S. federal minimum standard for energy efficiency.1
A boiler’s efficiency rating is dependent on how much fuel is wasted and how much fuel is used to produce a specific amount of heat. This is measured by something called the Annual Fuel Utilization Efficiency Rating (A.F.U.E.). Boilers with an A.F.U.E. rating of 85% or higher are considered to be high efficiency. Boilers with an ENERGY STAR label are tested to meet strict efficiency specifications and are certified by an independent third party. They perform the same as or better than standard products without compromising performance in any way.**
Legal disclaimers: 1 - https://www.energystar.gov/products/most_efficient/boilers
**- https://www.energystar.gov/products/heating_cooling/boilers&nbsp;