i just started to get rid of my old tankless heaters that were 178k btu that were 25 years old and 2.7 max flow at 45 degree rise or 1 gpm at 77 degree rise with new ones that are 100k btu with 3.7 gpm max flow and 2.3 gpm with a 77 degree rise for my hot water for the bays and for my floor heat. they are MAREY GA14CSANG