Rinnai Tankless Water Heater Installation

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Installing a Rinnai tankless water heater is a smart upgrade that delivers energy-efficient, on-demand hot water, but proper installation is essential for safety, performance and longevity. This installation guide breaks down the process into clear, easy-to-follow steps, helping you confidently set up a Rinnai system while meeting requirements and maximizing efficiency.

How to Install a Rinnai Tankless Water Heater

Mount the Internal Water Heater

Step 1. Level Wall Mounting Bracket – Hold the wall mounting bracket firmly against the wall and use a level to ensure it’s perfectly even.
Step 2. Secure Mounting Bracket to Wall – Attach the wall mounting bracket using four screws, two on the far left side and two on the far right side. Use the correct screws based on your wall material and secure the bracket into studs to properly support the unit’s weight.
Step 3. Install Water Heater Top Bracket – Carefully insert the unit’s top bracket into the mounted wall bracket. Before fully releasing the unit, confirm that the mounting bracket is stable and capable of supporting the weight of the tankless water heater.
Step 4. Fasten Top and Bottom Brackets – Secure both the top and bottom brackets to the wall using screws, ensuring all screws are tightened until flush with the wall surface.
- Note: Use any available mounting holes on the brackets.

Mount the External Water Heater

Step 1. Secure Top and Bottom Brackets – Fasten both top and bottom brackets to the wall using screws. Tighten each screw until it sits flush against the wall surface to ensure a secure installation.
Step 2. Use Available Mounting Holes – Choose any of the holes in the top and bottom brackets to anchor the unit. Choose positions that provide the strongest support based on your wall structure.
Step 3. Confirm Proper Level Alignment – Use a level to confirm the water heater is perfectly straight.
Step 4. Confirm Weight Support and Stability – Confirm that your mounting method can safely support the full weight of the water heater.

Vent the Water Heater

Step 1. Install Water Heater Unit – Mount and secure the tankless water heater.
Step 2. Choose Vent Termination Method – Determine the appropriate venting configuration for your system, like horizontal or vertical termination, concentric venting, or twin pipe venting.
Step 3. Identify Vent Penetration Locations – Plan and mark the correct locations for wall or roof penetrations based on your chosen vent termination method. Ensure adequate clearance and compliance with local codes.
Step 4. Install Vent Termination Assembly – Install the vent termination components according to the instructions in your Rinnai manual or the vent manufacturer’s guidelines.
Step 5. Connect Vent and Air Piping – Run and connect the combustion air intake and exhaust vent piping from the water heater to the termination point. Ensure all connections are secure and leak-free.
Step 6. Apply Proper Exhaust Pipe Slope – Slope the horizontal exhaust pipe toward the water heater at a rate of 1/4 inch per foot. DON’T slope the combustion air intake pipe toward the water heater.
Step 7. Install Vent Supports and Brackets – Secure the vent piping with proper supports and brackets. Allow for expansion and movement due to temperature changes, following manufacturer instructions and local building codes.
Step 8. Install the Vent Screen – Attach the provided vent screen to the PVC combustion air and exhaust termination elbows. Press the vent screen firmly inside the termination elbow. Secure the screen using the screw provided.

Connect Water Supply

Step 1. Connect Cold Water Supply Line – Attach the cold water supply line to the 3/4-inch MNPT connection at the bottom of the water heater labeled “COLD.” Make sure the connection’s tight and properly sealed to prevent leaks.

Step 2. Connect Hot Water Supply Line – Connect the hot water line to the 3/4-inch MNPT connection labeled “HOT.” Confirm that all fittings are secure and aligned correctly for optimal water flow.
Step 3. Check Pipe Cover Clearance (as needed) – If you plan to install a pipe cover, confirm that both the hot and cold water lines fit within the cover’s dimensions. Adjust piping as needed to ensure proper fit and installation.

Install the Isolation Valves

Step 1. Position Hot Isolation Valve – Place the hot isolation valve (red) directly below the hot water outlet on the tankless water heater, making sure it’s aligned properly.
Step 2. Hand-Tighten Hot Valve Connection – Thread the swivel nut of the hot isolation valve onto the hot outlet connection. Hand tighten it securely before using tools.
Step 3. Adjust and Tighten Drain Valve – Rotate the drain valve into a position that allows easy access for maintenance. Use a wrench to fully tighten the swivel nut, ensuring a secure, leak-free connection to the water heater.
Step 4. Install Cold Isolation Valve – Repeat Steps 1–3 to install the cold isolation valve (blue) on the cold water inlet side of the unit.
Step 5. Connect Cold Water Supply Line – Attach the cold water supply line to the cold isolation valve. Confirm the connection is properly sealed and secure.
Step 6. Connect Hot Water Supply Line – Connect the hot water supply line to the hot isolation valve. Tighten all fittings to prevent leaks and maintain consistent water flow.
Step 7. Verify Drain Valves Closed – Before turning on the water supply, make sure both drain valves are fully closed to prevent leaks.

Install the Pressure Relief Valve

Step 1. Attach Pressure Relief Valve Assembly – Locate the pressure relief valve connection on the bottom of the tankless water heater and hand tighten the pressure relief valve assembly and gasket onto the pressure relief valve union fitting. Make sure the gasket is properly seated.
Step 2. Position and Secure Valve – Rotate the pressure relief valve assembly to an accessible position for future maintenance and inspection. Using a wrench, tighten the union nut securely to the pressure relief valve union fitting. Make sure not to overtighten the connection to avoid damaging the threads.

Connect the Condensate Drain

Step 1. Apply Thread Sealant – Apply thread sealant to the 1/2-inch MNPT condensate drain port to ensure a leak-free connection.
Step 2. Install Drain Fitting – Thread a 1/2-inch NPT fitting onto the condensate drain port. Tighten securely to prevent leaks while avoiding overtightening.

If a condensate pump is part of your system, follow the wiring steps below to ensure proper safety operation.

Step 3. Disconnect Power to Water Heater – Turn off and disconnect all electrical power to the unit before beginning any wiring work to ensure safety.
Step 4. Access Safety Switch Wires – Remove the water heater cover and locate the two white wires labeled “To Condensate Pump Safety Switch.”
Step 5. Prepare Existing Wires – Cut off the crimp connectors from the white wires and strip the insulation from the wire ends to prepare for connection.
Step 6. Prepare New Wiring – Select a suitable length of wire (18 AWG or larger) and strip the insulation from both ends. Follow all wiring standards outlined in the National Electrical Code (NEC) for safe and compliant installation.
Step 7. Connect to Condensate Pump Safety Switch – Using wire nuts or other approved wire connectors, connect the “To Condensate Pump Safety Switch” wires to the normally open contacts on the condensate pump. Make sure all connections are secure and properly insulated.
Step 8. Restore Power and Test System – Reconnect power to the water heater. Press the “On/Off” button on the controller to power on the unit and verify proper operation.

Connect the Gas Supply

Step 1. Install Manual Gas Shut-Off Valve – Install a manual gas control valve in the gas supply line leading to the water heater. A union fitting can be added above the shut-off valve to allow for easier future servicing or disconnection of the unit.
Step 2. Verify Gas Type Compatibility – Check the gas type (natural gas or propane) and supply pressure before making any connections. Don’t connect the water heater if the gas type does not match, contact your dealer for the correct unit.
Step 3. Check Gas Supply Pressure – Measure gas supply pressure upstream at the location specified by your gas provider.
Step 4. Test All Gas Connections for Leaks – Before operating the unit, check all gas joints, including the water heater, for leaks using a soap solution, gas leak detector or nonflammable testing solution. Rinse piping with water after testing if the solution used is corrosive.
Step 5. Connect Gas Line – Use approved gas connectors to attach the water heater to the gas supply line. Purge the gas line of any debris before completing the connection to prevent damage or blockage.
Step 6. Use Proper Thread Sealant – Apply a thread sealant that’s resistant to liquefied petroleum gas (LP/propane) on all threaded gas pipe joints to ensure safe and durable connections.
Step 7. Confirm Proper Gas Line Sizing – Ensure the gas supply line is correctly sized and installed to meet the maximum demand of the water heater and all other gas appliances without pressure loss.
Step 8. Perform Final Leak and Pressure Test – Conduct a complete leak and pressure test before operating the water heater. Don’t turn on the unit if any leaks are detected—repair all leaks first to ensure safe operation.

Connect the Power Supply

When you’re connecting the unit to a power supply, follow these guidelines for best practices:

Use Proper Grounding Methods – Don’t use gas or water piping to ground the water heater. Always use the designated grounding points inside the unit.
Ensure Correct Power Supply – The water heater requires a 120 VAC, 60 Hz power supply from a properly grounded electrical circuit.
Plug Into a Grounded Outlet (Indoor Models) – For indoor units with a supplied 5-foot power cord, plug the unit into a standard 3-prong grounded 120V outlet.
Install an Outdoor Disconnect Switch (Outdoor Models) – External models must have a properly rated outdoor disconnect switch installed for the incoming 120 VAC power supply.
Follow National Electrical Code (NEC) ANSI/NFPA 70 and local code requirements when selecting and installing the switch.
Protect Electrical Connections – Ensure all power connections are protected from weather exposure. Use proper strain relief fittings for any flexible cords.
Reference the Wiring Diagram – Always consult the wiring diagram located inside the front cover of the water heater when making electrical connections.

Configure Parameter Settings

Step 1. Locate PC Board – Open the unit and find the PC board on the lower right side of the water heater.
Step 2. Identify Control Buttons – Locate the two push buttons labeled “A” and “B” on the PC board.
Step 3. Enter Parameter Mode – Press and hold the “A” button for 1 second to access the parameter settings mode.
Step 4. Select Setting Number – Use the up arrow and down arrow buttons on the controller to scroll through and select the desired setting number.
Step 5. Adjust Selected Setting – Press the “On/Off” button on the controller to change the selected setting.
Step 6. Exit Parameter Mode – Press and hold the “A” button for 1 second to exit the parameter settings menu and save your changes.

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