ASME approved pressure vessel constructed of high quality 439 Stainless Steel;Heat exchanger performance maximized through a multi-tube, counter-flow fire-tube design;Vertical combustion chamber and a down-firing burner allow gravity condensate drainage;Turn-down ratio of 10 to 1;50 psi maximum pressure;Metal fiber knit burner;Direct spark ignition;Brushless DC fan;Zero governing gas valve;Boiler shipped with 30 psi relief valve