*PLUMBERSSTOCK EXPERT* responded:
Hi! Thank you for asking about the Whitlam FLOW32 Flow-Aide liquid system descaler. We understand that you have 2 Rinnai systems but we cannot, for sure, recommend a certain amount to use in cleaning them using the Whitlam FLOW32 unless we know their product numbers or see a picture of them. Plus, the manufacturer of the product recommends that you should have your water lines and water heater systems serviced by a professional contractor. If you would like to send us a picture, please do so through email@example.com. Should you have further questions, please ask away! Thank you for visiting Plumbersstock.com. Have a great day!