The Elite ULTRA Duo boilers from HTP include dual heat exchangers that provide built-in operational redundancy. With firing rates between 285,000 to 399,000 Btu/h, the boiler guarantees energy savings with up to 96% AFUE. The turndown ratio of up to 20:1 limits short cycling and provides more efficient energy consumption. Cascade up to four Duo boilers to further increase redundancy and provide up to an 80 to 1 turndown ratio.