Up to 87.6% 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;9 Sizes Available (3-6 sections);Packaged or Knockdown Boilers;Cast Iron Sections;Factory Tested and Assembled with Steel Push Nipples;Large Water Content, Wet Base Section Design Ideal for Steam and Large Volume Hot Water Applications;Insulated, Deluxe Powder Coated Steel Jacket Reduces Boiler Heat Loss;Full Plate Swing-Out Door For Quick and Easy Cleaning;Optional Tankless Coils for Domestic Hot Water