The cold start boiler will not maintain any water temperature. It will only fire on a demand for heat or hot water. The tankless coil version will maintain temperature all the time in the event you need hot water feeding the chimney heat 24/7. My prefference with an indirect water heater is a cold start boiler if not a real large boiler to try to build up enough hot water before you run out. If this is a residence it is not aa problem. : What is the difference between a cold start boiler and a tankless coil heater. Is either one prefered when using it in cojunction with an indirect fired waster heater? thanks in advance.