Up to 87.5% AFUE;ENERGY STAR Certified - certain firing rates;All Models - DOE 2021 Compliant!;Natural Draft (Chimney) Venting;High Efficiency, Flame Retention Burners;Choice of Beckett, Carlin or Riello 2;Cast Iron Sections - Factory Tested and Assembled with Steel Push Nipples;Wet Base Section Design Ideal for Steam and Hot Water Applications;Rear or Top Flue Convertibility (certain models);Insulated, Deluxe Powder Coated Steel Jacket Reduces Boiler Heat Loss 4;Full Plate Swing-Out Door For Quick and Easy Cleaning 5;Built-in Air Elimination Baffle