The annual fuel utilization efficiency (AFUE) of a furnace or boiler is the measurement of the appliance's annual operating efficiency. For water heaters, its energy factor (EF) represents the efficiency. All of these efficiencies are measured under laboratory conditions using a Department of Energy (DOE) test procedure. Since the original federal minimum efficiency standards were enacted into law in 1987, updated minimum efficiency requirements for water heaters went into effect in 2004, and DOE has been working to update the current minimum efficiency standards for furnaces and boilers. All heating appliance manufacturers have a significant number of higher efficiency models. More homeowners are seeing the value in upgrading their homes' systems with new high-efficiency products.
The vent-system installation of highly efficient appliances requires a closer look. Be sure vent sizing and materials and installation of the vent are appropriate in order to ensure safety and optimal system performance.