The AM Series of boilers and water heaters features an advanced, high-efficiency condensing hydronic technology that produces installation, operating, and lifetime cost advantages to systems operating from 399,000-1 million Btuh. The units feature a patented modular design, efficiencies up to 98 percent, and turndown up to 20:1. Each module has its own gas valve, blower, burner, and combustion controls and safeties, so one boiler or water heater provides the security of a multi-unit system. The patented Variable Radial Circulation heat exchanger features three concentric stainless steel coiled tubes. The round tubes and parallel path combine to make for a lower pressure drop while simultaneously discouraging scale buildup. Long life is also supported by automatic rotation of the lead-lag modules and the minimal cycling that reduces wear on unit components. Equipped with Modbus communication, each unit can be integrated into a boiler management system (BMS) for greater operational efficiency of multiunit systems.