The 15B Series features an efficiency of up to 82%. The quality cast iron heat exchanger design is robust providing homeowners with a long-life, high output boiler in the smallest possible space. The hi-limit control has been separated from the circulator relay for ease of serviceability. The Argo Z99 control operates the circulator, damper and gas valve incorporating “Ice Cube” relay technology. When utilized in a seven section configuration the 15B Series can reach nearly 300 MBH input.