I have a house with very inefficient gas boiler, one 1â€ one way single loop pipe and 7 cast iron radiators. I wanted to replace this system with a radiant open system for the reason that is the most efficient system. I bought all the supply necessary to build that system including 2 Takagi TH2 high efficiency water heaters, but then I found that the city doesnâ€™t aloud this kind of system for the legionnaire bacteria concern. Those cast iron radiators can work very nice if I have a decent efficient boiler. My question is: can I use this Takagi TH 2 which is 90% efficient with the existing one way T connectors for every Â½ â€œ risers and cast iron boilers and new mechanicals and controllers for single zone? I heard that instant water heater are not like heat boilers to accept hot water for intake but Takagi use them also for heating applications because it can go to 180F.Does anybody has any experience for cast iron radiators and TH 2 water heater?