The Rinnai 104000032-K Water Heater Heat Exchanger Kit transfers heat to the water flowing through the water heating system. This assembly uses heated surfaces and internal water passages to transfer thermal energy from the burner to the incoming water during operation. Installed within the water heater, it connects with the heating system and supports the process of raising water tem... https://www.hnkparts.com/104000032-k-rennai-kit-heat-exchanger-r75lsi-r5/4-104000032-K.html