The Rinnai 107000147 Water Heater Heat Exchanger Kit transfers heat to the water flowing through the C199 water heater. This assembly uses heat generated by the burner and transfers it through internal passages as water moves through the exchanger. Installed within the water heater, it operates as an essential part of the heating system, supporting the transfer of thermal energy to pr... https://www.hnkparts.com/107000147-rennai-kit-heat-exchanger-c199/4-107000147.html