The Ultra 155 delivers 155 MBH at over 92% AFUE and up to 98% for low temperature applications. The Ultra features PhD (Precision Hydronic Data) Technology which is an intelligent system that delivers precision hydronic heating and hot water needs while maximizing efficiency by measuring and responding to the Data parameters of your heating system. Available models: Ultra 80, Ultra 105, Ultra 155, Ultra 230, Ultra 310.