The ultraclean condensing furnace, from Oak Ridge National Laboratory, achieves more than 99.9% acidic gas removal (including ~100% SOx trapping removal, >95% NOx redox to N2, and ~100% formic acid/CO/HC/CH4 oxidation) and has a potential AFUE of up to 98% at low cost. Thus, the AGR-enabled condensing furnace generates eco-friendly condensate with a pH of 7.0 while achieving ultra-clean flue gas. The eco-friendly condensate allows a simpler and less expensive furnace design that adopts a low-cost large secondary HX to maximize furnace efficiency. Moreover, the eco-friendly condensate allows for discharge into a city sewer system, eliminating the need for a secondary drainage system. The AGR technology can be directly integrated into current furnace designs without changing the furnace manufacturing process. The environmental benefits, cost savings, and simple installation advantages of the ultraclean and efficient furnace fitted with AGR technology will increase the market penetration of clean, efficient condensing furnaces. The AGR-enabled furnace technology can be used in both residential and weatherized condensing furnaces.