Rinnai, Navien, Rheem: How to Install Any Gas or Propane Tankless Water Heater

You’ve got a new tankless unit and you’re staring at the box, wondering if you’re about to flood your basement or cause a gas leak. Good. That’s the right place to start.

This guide walks you through the job from unpacking to first hot shower. We will cover what you need before you touch a tool, running new gas lines, proper venting, and the final configuration for maximum performance.

I’ve installed these in my own house and on hundreds of service calls. The takeaway is simple: the right wrench and a methodical setup beat rushing it every time.

The DIY Reality Check: Should You Install Your Own Tankless Water Heater?

Let’s be direct. A full tankless water heater installation is an 8 out of 10 on the difficulty scale for a DIYer. The water lines are the easy part. The complexity comes from the gas and the venting. A small mistake here isn’t a drip, it’s a fire or carbon monoxide hazard.

You can save money and time by handling some tasks yourself. A pro can then finish the critical connections. Here’s the split.

What a Homeowner Can Realistically Do

• Mounting the unit to the wall studs. This is straightforward carpentry.
• Running the new cold and hot water supply lines. Using PEX or copper with simple sharkbite or sweat connections is within reach.
• Installing the included sediment filter on the cold water inlet.
• Mounting the exterior vent termination kit (but not running the vent pipe itself through the wall).

Think of your role as the preparation crew. You get everything ready for the specialist to do their precise work.

Non-Negotiable Pro Tasks: Call a Licensed Technician

These steps are not DIY. Your city requires it, and your safety demands it.

• All new gas line work. This includes sizing the pipe correctly and running it from the meter or main line.
• Final gas pressure testing and adjustment with a manometer. Your unit will fail without correct pressure.
• Venting system installation. Cutting holes through walls, running sealed PVC or stainless pipe, and ensuring proper slope is a code-specific skill.
• Electrical connections for condensing units (like Navien and most high-efficiency models). They need a 120V outlet, which often requires new wiring.

The Legal and Insurance Fine Print

Unpermitted gas work is a liability trap. If you sell your home, an inspector will flag it. Your home insurance policy will void coverage for any fire or incident linked to unpermitted work.

I had a situation with my own house. The previous owner left a large air compressor. It was plumbed in, but he specifically listed it as excluded in the sale documents. If he hadn’t, it would have had to stay. Anything permanently connected to your gas or water lines is considered part of the house. The law sees a water heater the same way.

Getting a permit and a licensed installer’s signature is your only guarantee that the work is legal and safe.

Gathering Your Gear: Tools and Parts for the Job

You don’t want to be on a ladder realizing you’re missing one fitting. This list covers a standard install for brands like Rinnai, Navien, and Rheem. Check your manual’s installation guide for model-specific requirements.

Hand Tools You’ll Need

• Two pipe wrenches (12-inch minimum)
• Tubing cutter for copper or a PEX cutting tool
• Deburring tool or file
• 4-foot level
• Drill/driver with masonry bits (for vent termination)
• Adjustable wrenches
• Screwdrivers (flathead and Phillips)
• Tape measure
• Pipe thread sealant (pipe dope) rated for gas and Teflon tape for water lines
• Hacksaw or reciprocating saw for cutting existing pipe
• Torch kit if soldering copper

Parts and Materials Checklist

Buy quality parts. Cheap gas fittings can leak.

• Gas pipe: Correct diameter black iron pipe or CSST flexible gas line (if local code allows).
• Gas connectors: Required dielectric unions, drip legs (sediment traps), and shut-off valves.
• Venting kit: This is critical. You must use the specific direct vent or concentric vent system listed for your exact model. A Navien vent kit will not work on a Rinnai.
• Water line fittings: Isolation valves (ball valves), unions for easy future service, and the correct adapters for your home’s piping (copper, CPVC, or PEX).
• Sediment filter: Most units include one, but have a spare cartridge.
• Condensate neutralizer kit and drain line tubing (for high-efficiency condensing units).
• Mounting hardware: Long, heavy-duty lag bolts for hitting wall studs.

The venting materials are not generic. Using the wrong type or size will cause the unit to fault and can fill your home with exhaust gas.

The One Specialty Tool That Surprises Everyone

You need a manometer. This tool measures gas pressure in inches of water column. Even if a pro does the final hookup, you can verify the existing house pressure before you start.

A proper install requires adjusting the gas valve to the exact pressure specified in the manual (usually between 3.5 and 10.5 inches WC). Guessing is not an option. You can rent a digital manometer from most tool rental shops.

Plan First: The Three Critical Systems to Map Out

You cannot just swap a tank for a tankless unit. A tank heater stores hot water. A tankless heater makes it instantly on demand, which puts a massive, sudden load on your home’s systems. You must plan for three separate pathways: gas, water, and vent. Get one wrong, and your new heater will fail or become unsafe. Don’t forget to understand how tankless water heaters work before installation.

The Gas Pathway: Your Engine’s Fuel Line

Think of your gas line like a garden hose. A small hose can fill a bucket slowly just fine. But if you need to power a pressure washer, that small hose can’t deliver enough water fast enough. Your old tank heater was the bucket. A tankless unit is the pressure washer.

To avoid a weak, lukewarm shower, you must verify your gas line can deliver enough volume (measured in BTU/hr) at the correct pressure. This is the most common planning mistake.

Here is how to check your gas system:

1. Find the gas line that runs to your current water heater. Measure its diameter. Common sizes are 1/2-inch, 3/4-inch, and 1-inch.
2. Check the BTU requirement of your chosen tankless model (found in the manual). A typical unit needs 150,000 to 200,000 BTU/hr.
3. Trace that line back to the meter. The entire run from the meter to the new heater location must be sized for the total load.

You will likely need to upgrade the main gas line from the meter. A 1-inch line is standard for most tankless installs. You also must test the incoming gas pressure with a manometer. You need a stable 7-11 inches of water column (WC) for natural gas or 11-14 inches WC for propane when the heater is firing. If pressure is low, you may need a larger gas meter installed by the utility company. This is not a DIY task.

The Water Pathway: Protect the Heart of the Unit

While the gas side is about volume, the water side is about protection and maintenance. Tankless heaters have small, complex heat exchangers that are easily damaged by mineral scale and debris. That’s why myths about tankless water heaters often creep in. Debunking those myths starts with understanding the actual maintenance and mineral-scaling risks these units face.

Always install full-port ball valve isolation valves on both the hot and cold water connections. The cheap quarter-turn valves you often see are not full-port and will restrict flow. I used brass valves on my own Rheem install. This lets you shut off water to service the heater without turning off water to the whole house.

Next, install a standard 50-micron sediment filter on the cold water inlet pipe before the heater. This catches sand, rust flakes, and other debris that will clog the internal sensors and flow valve. A $20 filter can prevent a $500 service call for a flow error code. Plan for easy access to clean this filter every few months. In the next steps, we’ll show how to replace the water heater filters themselves, including when to change and how to install a fresh one. Keeping this access point clear now will make those steps quick and easy.

The Vent Pathway: Getting the Fumes Out Safely

Tankless heaters are high-efficiency appliances. They produce acidic exhaust condensate that must be vented properly using special materials. There are two main venting types: power vent and atmospheric vent.

• Direct Vent (Sealed Combustion): This system pulls combustion air from outside through one pipe and exhausts fumes through a second, concentric pipe. It’s the safest option, as the burner is completely sealed from your home’s air.
• Power Vent: This system pulls combustion air from the room it’s installed in and uses a fan to push exhaust fumes through a single pipe to the outside. You must ensure the installation room has adequate fresh air ventilation.

Venting has strict clearance rules. The exhaust termination (the cap on the outside wall) must be placed correctly. Typical manufacturer requirements include:

• At least 12 inches from any operable window or door.
• At least 12 inches above ground level (to avoid snow blockage).
• At least 3 feet from any gas meter, electric meter, or fresh air intake.

You must use the vent kit specified for your exact heater model. Do not mix brands. The pipe must slope slightly back toward the heater to drain condensate into the unit’s internal neutralizer.

Choosing the Final Location: The Balancing Act

Your ideal location is the spot that best satisfies all three pathways with the shortest, most direct runs. Often, this is on an exterior wall where you can easily vent directly outside. The garage is a popular choice (that’s where mine is), but it must not be subject to freezing temperatures.

Walk through the checklist: Can you run a sufficiently large gas line here? Is there easy access for water lines and the required filter? Can you route the specialized vent pipe to an outdoor location that meets all clearances? Is there an electrical outlet nearby for the unit’s control panel (they all need 120V power)? If you answer yes to all, you have found your spot. Always confirm your plan against your local building code, which will have the final say.

The Core Installation Steps (Before You Touch the Gas)

This is the meat of the job. Get these steps right, and the rest flows smoothly. Get them wrong, and you’re setting yourself up for a major headache or a dangerous situation. Let’s start from the box and work our way to the moment before you connect the gas line.

1. Kill the Power and Water

This isn’t a suggestion. Go to your main electrical panel and shut off the circuit breaker for your old water heater. Use a non-contact voltage tester to confirm the wires are dead. At your main water shutoff valve, turn off the cold water supply to the entire house. Open a few faucets on the lowest and highest floors to drain down the pressure. Never work on plumbing or electrical systems with the utilities live.

2. Unpack and Plan Your Mount

Uncrate the unit carefully and lay out all parts. Find the mounting template in the manual. Hold it against your chosen wall. The wall must be structural-never drywall alone. You need solid wood or concrete block behind it. Consider future service; leave at least 12 inches of clearance on the side with the service panel and 18 inches above. Mark your drill holes. A wobbly mount stresses pipes and can cause leaks or vent failure down the road.

3. Run the Vent Pipe (The “Measure Twice, Cut Once” Step)

This step stops more DIY installs than any other. First, know your unit: direct-vent (pulls air from outside) or power-vent (pulls indoor air). Your manual dictates the exact pipe material, diameter, maximum length, and number of elbows allowed. For a DIYer, direct-vent is simpler. Dry-fit all vent pieces from the unit’s collar to the termination cap outside. Ensure the pipe slopes slightly back toward the unit for condensation drainage. A single extra elbow or foot of pipe over the limit will cause ignition failure and error codes.

4. Mount the Unit and Connect Venting

Using the correct masonry or lag bolts, secure the mounting bracket to the wall studs. Hang the unit. It should feel absolutely solid. Now, permanently assemble and connect your vent piping. Use high-temperature silicone sealant on the joints as specified by the manufacturer. For PVC/CPVC venting on some models, use the approved primer and cement. This connection must be airtight.

5. Plumb the Water Lines with Valves

Here’s a pro tip: install full-port ball valves on both the cold water inlet and hot water outlet lines before they connect to the unit. Use unions or flexible braided stainless connectors for the final hookup. This lets you isolate and remove the heater for service without shutting off your whole house water. Connect the cold line to the unit’s right port (marked with a blue ring) and the hot to the left (red ring). Those isolation valves are not optional if you ever want to service the unit without a full system shutdown.

6. Install the Sediment Filter

Most tankless makers require this, and even if they don’t, you should do it. Install a standard Y-pattern or spin-down sediment filter on the cold water line before it reaches the unit. Hard debris will destroy the internal heat exchanger. A 100-mesh filter is a good start. Point the filter bowl downward so you can easily clean it. I have one on my own Rheem, and it catches surprising grit every few months. For gas-fired tankless units, the tankless inlet filter is an important line of defense to keep sediment from entering the heat exchanger. Regular checks ensure the system stays efficient and reliable.

7. Pressure Test the Water Lines (The Critical Check)

Do not skip this. With the tankless unit’s internal valves still closed (if equipped) or the isolation valves closed, slowly turn your main house water back on. Open the cold water isolation valve. Now, systematically check every joint and connection you made-from the filter to the valves to the unit ports. Look for the smallest drip. Tighten connections as needed. A leak under water pressure is a flood waiting to happen when you add gas and heat. Finding and fixing a water leak now is cheap and easy. Finding one after the wall is sealed up is a nightmare.

Once your mount is rock-solid, your vent is perfect, and your water lines hold pressure with zero leaks, you’re ready for the next phase. The gas connection comes next, and that is a step I strongly advise leaving to a licensed professional.

Configuration and Startup: Getting the Hot Water Flowing

This is where your new tankless heater comes to life. Proper setup prevents callbacks and cold showers. Follow these steps in order.

Purging Air and Verifying Water Flow

Before you touch the gas or power, deal with the water lines. Open the main cold water shutoff valve to the unit slowly. Listen for hissing. That’s air trapped in the lines. You must purge it.

Go to the farthest hot water faucet in your house, like an upstairs bathroom. Turn it on fully to hot. Let it run for a solid three minutes. The water will sputter and spit at first, then run smooth. This pushes all the air out of the hot side plumbing. Purging air protects the heater’s internal flow sensor and prevents noisy, erratic operation.

Now check for leaks at all your new connections. A slow drip today is a flood tomorrow. My own Navien install had a weep at a union that I caught because I took this time to look.

The Gas Connection: A Job for a Licensed Technician

Here is the hard stop for DIY. Connecting the gas line and making final adjustments is not a homeowner task.

A licensed pro will use a manometer to measure gas pressure. Propane and natural gas systems need different pressure settings, usually listed on the unit’s rating plate. They will adjust the regulator to hit the exact pressure, often 3.5″ to 4″ WC for natural gas. Incorrect gas pressure is the top cause of error codes, soot buildup, and premature failure.

The technician will also perform a full leak check with soap solution on every joint. They will verify the venting is secure and clear. Do not skip this. Paying for this hour of labor is cheaper than rebuilding your house.

How to Adjust a Tankless Water Heater’s Temperature

Once the unit has power and gas, use the control panel. The buttons vary by brand, but the process is similar.

• Locate the temperature buttons. On Rheem and Rinnai, they are often up/down arrows. On Navien, you might press a “Mode” button first.
• Press to increase or decrease the set point. The display will show the temperature, usually in Fahrenheit.
• Set your desired output temperature. A common safe setting is 120°F.

Can you set a Rinnai tankless water heater above 120? Absolutely. Most models go up to 140°F or higher. Be cautious with high temperatures above 120°F to prevent scald risk, especially in homes with children or elderly residents. Also, review your unit’s water heater temperature safety settings to ensure anti-scald protection is active. This helps balance comfort and safety for all household members. If you need hotter water for a dishwasher without a booster, 130°F might be necessary. Adjust in small increments.

Output Setting vs. External Thermostatic Controls

The temperature you set on the unit’s panel is its default output. Think of this as the baseline.

Some systems, like advanced Navien or Rinnai models, can connect to external controls. These are separate thermostats or smart home modules. An external control can tell the heater to output a different temperature for a schedule or a specific faucet. The control panel setting is the maximum it will go if the external device asks for more heat. If your external thermostat calls for 110°F, the heater will deliver that, even if the panel is set to 130°F.

The Initial Startup Sequence

Your manual has the exact steps, but they all follow a common pattern. After gas and power are confirmed, the unit is in standby.

1. Go to a hot water faucet. Turn it on fully.
2. You should hear the unit’s fan start within a few seconds. Then, you’ll hear the gas valve click and the burner ignite.
3. Let the water run. It will be cold, then warm, then hot. This first startup can take a minute as the heat exchanger warms up.
4. Check that the temperature at the faucet matches what you set. Use a cooking thermometer if you need to be sure.

If the burner doesn’t light, the unit will usually flash an error code. Common first-time issues are blocked venting or a gas valve that isn’t fully open. Double-check those before you call for service.

Brand-Specific Nuances: Rinnai, Navien, and Rheem

Rinnai Installation and Adjustment

Rinnai units are known for reliability, but their venting system is particular. You cannot use standard PVC for exhaust on most indoor models. You must use Rinnai’s proprietary concentric vent kit or their specific AL29-4C stainless steel venting material for separate intake and exhaust. Trying to adapt standard PVC often leads to backdrafting or error codes. On the gas side, ensure your gas line is sized correctly; these units fire fast and need a full volume of gas immediately.

To adjust the temperature on a Rinnai, locate the control panel. The process is simple:

1. Press the Power button to wake the unit up.
2. Press the Temperature Up or Down button to set your desired output.
3. Wait a few seconds for the unit to beep, confirming the new setting.

Many newer models also have a “Mode” button to switch between a precise temperature setting and an Eco (lower temperature) mode.

Navien Installation and Adjustment

Navien’s condensing technology is highly efficient, but it creates acidic condensate. Most local codes and the manufacturer require a condensate neutralizer kit on the drain line. This is a small chamber filled with marble or limestone chips that neutralizes the acidic water before it enters your drain pipes. Forgetting this can corrode your plumbing over time. Also, Navien units often include a built-in recirculation pump option, which requires proper wiring and an under-sink return line kit for full functionality.

Here is how to adjust Navien tankless water heater temperature. You typically use the remote control or the front panel:

• Using the Remote: Press the “Temp” button, then use the up/down arrows to set the temperature. Press “Enter” to confirm.
• Using the Front Panel: Press the “Menu” button. Navigate using the arrow keys to the temperature setting (often labeled “Set Temp” or “Water Temp”). Press “Enter,” adjust with the arrows, and press “Enter” again to save.

If you have a recirculation system, you will find separate settings for its schedule in the same menu.

Rheem Installation and Adjustment

Rheem (and its sister brand, Ruud) are common finds. A frequent quirk on first startup is error code 11 (ignition failure) or 76 (low water flow). Before assuming a part is faulty, verify your gas supply valve is fully open and that your water flow exceeds the unit’s minimum requirement, usually around 0.5 gallons per minute. Another install tip is to pay close attention to the factory-installed wire connectors; ensure they are fully snapped into place on the control board, as a loose connection can cause intermittent faults.

Adjusting the temperature on a Rheem is straightforward:

1. Press the “On/Off” button to activate the control panel.
2. Repeatedly press the “Temp” button to cycle through the preset temperature options (often 120°F, 125°F, etc.).
3. The display will show the selected temperature. Wait a moment, and it will revert to showing the current output temperature.

Some advanced settings, like maximum temperature limit, require holding buttons in a specific sequence detailed in the manual. Many homeowners find that AO Smith tankless units, which often share similar internal components and control boards with Rheem, follow this same basic adjustment procedure on their front panels.

Navigating Permits, Inspections, and Final Safety Checks

Your pro installer will handle the heavy lifting, but you still own this process. Knowing what happens with permits and inspections keeps you informed and safe.

The Permit Process for a Gas Appliance

Think of a permit as your official receipt for a safe, legal installation. Your installer pulls the permit with your local building department. This legally transfers liability to their license and insurance. Never let a contractor talk you into skipping the permit, as it can void your homeowner’s insurance and create a huge headache when you sell your house. After installation, the inspector visits to verify the work meets code. Only after they sign off is the job officially complete.

What the Inspector Will Look For

The inspector’s checklist is all about safety and longevity. They’re not just ticking boxes, they’re preventing fires and carbon monoxide leaks. Here’s what they verify.

• Proper Gas Line Sizing: Tankless units need a big, instantaneous gas supply. The inspector will check that the new gas line from the meter is the correct diameter (often ¾-inch or 1-inch) to deliver enough BTU. An undersized line will cause the heater to fault and shut down.
• Correct Vent Material and Clearances: This is critical. They will confirm the vent pipe is the listed, sealed type (like AL29-4C for condensing units) and that it maintains the required clearance from windows, doors, and vinyl siding. Plastic vents can’t be used on non-condensing units.
• Sediment Filter: Most codes now require an inline sediment filter on the cold water inlet. The inspector wants to see it installed and accessible for easy future service.
• Drip Leg (Dirt Pocket): A small vertical pipe section with a cap at the bottom must be installed where the gas line meets the unit. This traps debris before it can clog the gas valve.
• Expansion Tank: If your home has a backflow preventer or check valve on the main line (creating a “closed” system), the inspector will require a thermal expansion tank on the water heater’s cold side.
• Proper Labeling: They’ll check for the unit’s data plate and any required warning labels. The gas shutoff valve must be clearly identified.

Your Final Safety Checklist (After the Pro Leaves)

The inspector passed it, but you live with it. Run through this simple list over the next few days.

• Monitor for Error Codes: Turn on a few hot water fixtures at once to put the unit under load. Watch the display. A solid number is your temperature. A flashing code indicates a problem. Have your manual ready to decode it.
• Check for Unusual Smells or Sounds: Sniff around the unit briefly when it fires. You might smell dust burning off the heat exchanger for a few minutes, but a persistent rotten egg or gas smell is an emergency-evacuate and call the gas company. Listen for a smooth ignition and a steady hum. Loud bangs, rattles, or whistling from the vent are red flags.
• Verify Consistent Hot Water Temperature: Run a shower and a sink elsewhere in the house simultaneously. Does the temperature hold steady or does it plummet or surge? Fluctuations can point to a gas supply or flow sensor issue.

Your first month of gas and water bills will be your final test, showing you the efficiency gain from your new tankless system.

Who to Call If Something Isn’t Right

You hear a strange hum or see an error flash. Your first call is to the installing technician’s company, not a general handyman. They know exactly how your system was configured and their work is under warranty. A random handyman might void your unit’s warranty by tampering with gas or sealed combustion parts. Keep your installer’s invoice and contact info in the unit’s manual. If the installer is unresponsive, contact the manufacturer directly for a certified service tech in your area.

Common Questions

Is the installation different for propane vs. natural gas?

Yes, the core difference is the gas pressure. Propane systems operate at a much higher pressure (11-14 inches WC) than natural gas (3.5-10.5 inches WC). Your unit will come configured for one fuel type, and a licensed technician must install the correct gas valve orifice kit and adjust the regulator pressure with a manometer. Using the wrong setup is dangerous and will damage the heater. Converting your water heater to a different gas type requires professional handling to ensure safety and functionality.

I’m getting an error code on first startup. What should I check first?

Before calling for service, verify three things. Ensure the main gas shutoff valve to the unit is fully open. Check that your vent termination outside is clear of any debris or blockage. Finally, confirm your hot water faucet is flowing above the heater’s minimum required rate (usually 0.5 GPM). These simple oversights cause most initial error codes.

How do I adjust the temperature on my specific brand?

For Rinnai, use the up/down arrows on the control panel. For Navien, you’ll typically use the “Menu” or “Temp” button on the remote or front display. For Rheem, press the “Temp” button to cycle through presets. Always consult your manual first, as menus vary by model-changing the max limit often requires a special button sequence.

Do I really need to upgrade my gas line from the meter?

Almost certainly. A standard tankless heater demands 3-4 times the gas volume of a old tank model at the instant it fires. An undersized line will cause poor performance, sooting, and lockout errors. A licensed technician must calculate the total BTU load and run the proper diameter pipe (often 1-inch) from the meter to ensure adequate supply.

What’s the one maintenance task I should never skip?

Flushing the sediment filter. That small filter on your cold water inlet is your heater’s first line of defense. Check and clean its screen every 3-6 months, or as stated in your manual. Letting it clog reduces water flow, triggers error codes and forces the heater to work harder, which shortens its lifespan.

Final Steps for a Reliable Tankless System

Always follow the manufacturer’s installation guide for your specific model to avoid costly mistakes. Test the water heater under full demand to confirm it meets your home’s hot water needs.