Oil boilers burn oil to heat water and then distribute heat to the home via radiators, an integrated duct system, or through radiant floor heating loops. High efficiency oil boilers use sealed-combustion with two ducts that fully isolate the combustion process. This includes one that draws combustion air from outside the home and one that exhausts flue gases directly outside. Thus, sealed combustion eliminates the possibility of back-drafting harmful flue gases back into the home or consuming too much oxygen. These boilers optimize efficiency with a condensing process that extracts heat with a secondary heat exchanger., High-efficiency oil boilers meet ENERGY STAR requirements for efficiency. Ultra-efficient oil boilers meet or exceed the criteria for ENERGY STAR’s “Most Efficient” designation.