Frequently Asked Questions

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Without a Rinnai recirculation system, it’s normal to have a slight 1 - 2 second temperature drop as the water in the pipes clears the line. The wait time to get hot water is dependent on the distance between your Rinnai tankless water heater and the location of any hot water faucet within your home for an endless hot water supply.

The wait time to get hot water is primarily determined by the distance between the water heater and the point of use. Rinnai tankless hot water heaters produce hot water within just a few seconds of first water flow from a cold start. However, all the cold water must be purged out of the pipe between the hot water heater and your point of use. For example, if your kitchen sink is 50 feet from the hot water heater and the water flow rate is one gallon per minute, it will take 90 seconds or so for hot water to reach your sink.

Because of their small size, you can place Rinnai tankless water heaters in locations that you could never place a tank. If you have your Rinnai hot water heater close to your primary points of use—such as the kitchen or master bath—you’ll drastically reduce the wait time.

By design, the fan will keep running for a short time after the flow of water stops. This helps ensure constant water temperatures during rapid starting and stopping, as well as exhausting any residual gas flue products from the unit. It will turn off on its own after a few moments.

A Rinnai tankless water heater features built-in freeze protection. When protected from direct wind exposure and connected to both power and gas, the water heater offers freeze protection down to -22°F (-30°C) for indoor models or as cold as -4°F (-20°C) for outdoor models. Though the water heater itself is protected from freezing, plumbing and valves to the water heater are not. Therefore, pipes and valves going to the water heater must be heat traced and insulated to protect them from freezing.

A professional plumber will follow installation recommendations so your unit can operate optimally, even in cold weather.

Your tankless water heater will feel cold to the touch when the heater unit and pumps are in the rest state and not heating water. There’s nothing to worry about. As long as everything is working properly (e.g. you have hot water on demand), there is no cause for concern.

Error codes vary based on product. Please contact Rinnai or your local installer to troubleshoot the codes and find the root cause. Send us a message or call our Customer Care team at 1-800-621-9419. We are available Monday through Friday, 8 a.m. to 8 p.m. EST.

Don’t worry: That “smoke” is likely just water vapor. During cold weather, when the exhaust temperature is much hotter than the outside air, the exhaust fumes condense producing water vapor.

Buyer's Information

Typically you won’t notice a difference in hot water performance when you have low-flow faucets or showerheads. If you find you’re not getting the hot water you need, start by lowering the temperature setting on your tankless water heater by a couple of degrees. It’s counterintuitive, but it affects the hot/cold mix ratio and will activate the tankless water heater unit for lower-flow fixtures.

Also, remember many single-handle faucets have limit stops that affect the hot/cold mix and may need to be adjusted. If this is the case, it may be helpful to check with the manufacturer of your faucet or consult the faucet manual for details on how to make these adjustments.

Good news! We have specific tankless water heaters for mobile homes and modular homes. There are compatible units include both our Luxury and Value Series. A certified dealer or installer will be able to offer advice on which Rinnai tankless water heater will best suit your needs.

The Hugo X-1 is a battery backup system — also known as an Uninterrupted Power Supply (UPS) — for tankless water heater products and more. Designed specifically to run your Rinnai tankless unit without power for multiple days, The Hugo X-1 will also keep your computer or cellphone powered until power is restored. The Hugo X-1 is available now for order from your local Rinnai Ace Dealer.

If you experience a power outage, your Rinnai Tankless Water Heater will not operate. However, the Hugo X-1 Battery Backup, designed specifically to run your Rinnai tankless unit without power for multiple days, will also keep your computer or cellphone powered until power is restored. The Hugo X-1 is available now for order from your local Rinnai Ace Dealer.

There are many factors that impact the size of tankless water heater you should choose, including how many people are in your home or office and how many facilities (bathrooms, washrooms, laundry rooms or kitchens) the unit will service. To simplify the process, we have a handy three-step formula for choosing what capacity of Rinnai tankless water heater will work best for your needs.

Step 1: Identify your required flow rate in gallons per minute (GPM)
Step 2: Identify the groundwater temperature in your region or state
Step 3: Calculate your required minimum temperature riseFor help with identifying the perfect tankless water heater contact a licensed and trained professional to guide you from the beginning, click here to find one in your area.

The life expectancy (or useful lifespan) of a Rinnai tankless water heater is up to 20 years. Actual life is impacted by water quality, usage and proper maintenance. For comparison, a tankless water heater lasts about twice as long as a tank water heater, making them a better value in the long run.

A traditional tank water heater is the most common type in the United States and Canada. These tank heaters use older, less efficient technology to gradually heat cold water at the bottom of the large tank. That means that the water in the tank is constantly being heated, waiting for the moment when you need it. Rather than storing water, tankless water heaters use heating coils to heat on demand as you need it. Tankless water heaters are more energy efficient, use less physical space and provide technology not typically available with tank water systems.

Rinnai tankless hot water heaters can’t be used for heating pools or spas because the chemicals necessary for those fixtures would damage the components of the water heater.

The Energy Policy Act of 2005 established tax credits for energy improvements to existing homes. If you choose a tankless gas water heater, hybrid gas water heater or natural gas tankless water heater which has either an energy factor of at least 0.82 or a thermal efficiency of at least 90%, you may be eligible for tax credits.

Check directly with or your tax professional to learn more about a potential credit.

There are many advantages of a tankless water heater over a traditional tank unit. One of the main benefits is an endless supply of hot water. You can have multiple showers, a load of laundry and the dishwasher running simultaneously and they’ll all have all the hot water they need. Another big benefit is virtually instant hot water. Rather than waiting several minutes for the water to heat up, your tap will turn hot in seconds. With a Rinnai tankless hot water heater, you’ll save space since they’re a fraction of the size of a traditional tank, and you’ll save in energy costs, thanks to superior energy efficiency. Plus, tankless water heaters have approximately double the expected useful life of a tanked unit. A tankless hot water heater outperforms a water heater tank in just about every way.

Rather than storing water, tankless water heaters use heating coils to warm the water as you need it. That’s why tankless water heaters are often called “on-demand water heaters.” When you open a tap or start an appliance such as a dishwasher, the tankless water heater recognizes the need and begins to deliver hot water when and where you need it. This is much more energy efficient for hot water heating versus traditional tank water heaters, which constantly heat water, even when none is needed.

Both Lowe’s and The Home Depot are trusted national retailers of Rinnai tankless water heater products. They carry a wide variety of options, sizes and capacities, so you can choose the Rinnai tankless gas water heater that best suits your needs and space. They also carry the necessary additional components (such as venting and recirculating pump parts) that may be necessary for a licensed contractor to install your unit. It’s important to note that we recommend installation by a licensed contractor. Click here to find a Rinnai-trained professional.

In August 2016, Consumer Reports provided a Water Heater Buying Guide to help consumers find the best water heater. In the article, they compared various types of water heaters including tankless (on-demand) water heaters, storage tank water heaters, heat pump or hybrid water heaters, solar water heaters and condensing water heaters.

Installing a tankless water heater may be more expensive than installing a traditional water heater tank because certain homes may require changes to some of the HVAC ducts or installing certain necessary plumbing pipes. The cost varies based on a number of factors, including where you live, how your home is constructed, which plumber you choose and which Rinnai tankless water heater you select. For an accurate price, click here to find one in your area.

Rinnai is the original pioneer of the tankless water heater, and for over 100 years Rinnai has focused on innovation and quality. The extreme flow rate of hot water to multiple faucets, appliances and showers simultaneously, space savings and high energy efficiency all point to Rinnai as the world leader in gas tankless water heaters.

A tankless water heater saves you money over time, thanks to far superior energy efficiency.
They have a significantly longer useful lifespan than tank water heaters, lasting almost twice as long in some cases.
They require significantly less storage space than a storage tank water heater.
You’ll have unlimited hot water whenever you need it. The hot water is available in seconds instead of the minutes it typically takes for a tank heater.
You will have more than enough hot water for multiple showers and appliances to run simultaneously.

Tankless water heaters generally have a higher purchase cost, when compared with traditional storage tank water heaters.
Installation can be more expensive, based on how much (if any) retrofitting is needed.
You could be “output challenged” if maximum usage was calculated incorrectly. Fortunately, we have tools to help you and your installation professional choose the right Rinnai unit for you, avoiding this issue.
For an exact installation and unit price, click here to find a licensed dealer in your area.

There are many benefits of choosing a tankless water heater over a traditional tank heater. Rinnai tankless water heaters provide an endless supply of hot water (24/7) that is practically instantaneous and keeps your energy bills down. Plus, you don’t need a large space to accommodate it. A smaller footprint dedicated to the hot water heater allows you to place your tankless water heater where you want it (indoors or outdoors, according to which model you choose). Finally, a tankless water heater can last twice as long as a traditional tank heater, offering better value in the long-run.

They do not. Instead, Rinnai tankless gas water heaters have a direct-spark electronic ignition.

Unfortunately, our tankless water heaters cannot be used in houseboats or recreational vehicles (RVs). However, we do have units made to be compatible for installation in mobile and modular homes.

The estimated life expectancy of a Rinnai tankless hot water heater is twice as long as that of a traditional tank.* Actual performance will vary depending on water quality, usage rates, environmental conditions and regular maintenance. This longevity is one of the factors that makes a Rinnai tankless water heater a money-saving choice over time.

*Based on DOE ENERGY STAR® lifecycle estimates

Rinnai tankless gas water heaters need a demand of at least 0.4 to 0.6 gallons per minute of water flow through the hot side to ignite and 0.26 gallons per minute to stay in operation. If the flow rate falls below these levels, the energy-efficient Rinnai unit will turn off because it senses that hot water isn’t needed.There are several possible solutions to minimum flow rate issues. You can try lowering the temperature on the unit to avoid cutting in too much cold water; cleaning the inlet water filter on the cold water inlet of the unit to remove sediment buildup that can decrease flow; cleaning or removing the aerators from showerheads or fixtures; or replacing low-flow showerheads or fixtures. If you believe that none of these are the issue, contact your original installer or plumber to service the unit.

Good news: The short answer is yes. Rinnai tankless water heaters feature freeze protection for outside temperatures as cold as -22° F (-30° C) for indoor models or as cold as -4° F (-20° C) for outdoor models when protected from direct wind exposure and as long as the appliance has both power and gas supply. The pipes feeding the unit must be heat-traced and insulated to provide the necessary freeze protection.

Rinnai strongly recommends the installation of an optional drain-down system on units installed outside in cold climates. Once installed, the system allows water inside the unit to drain out if there’s a power and/or gas outage or a component failure. See the owner’s manual for optional drain-down system piping.

Rinnai Tankless Water Heaters are not UL-rated but they are certified by CSA International to ANSI Z21.10.3 Standard Gas Water Heaters, Volume III, Storage Water Heaters with Input Ratings Above 75,000 Btu/h. However, the following internal electrical components are UL-certified:

Transformer E (UL 1411)
Relay (UL 41515)
Wire & Conduit (UL 1430)

Rinnai Tankless Water Heaters operate using natural gas or propane and have an electronic ignition.

We don’t make an electric model, because there are several potential drawbacks to electric tankless water heater units. First, the power requirements of electric units large enough to provide hot water for a typical household can be prohibitive. For example, a unit that can provide three gallons per minute with an 80° F temperature rise would require about a 150 amp 230 VAC circuit. That’s about eight times the power required for a three-ton central air conditioning system!Second, the relative operating cost of electric tankless water heaters is much higher than gas water heaters. Based on national averages, electricity costs nearly twice as much per BTU as natural gas. Even with propane, gas tankless water heaters are considerably less expensive to operate than those that run on electricity.


What size gas line does a Rinnai Tankless Water Heater require? Rinnai Tankless Water Heaters are designed to provide maximum performance and efficiency using either a 3/4" or 1/2" gas line, as long as sufficient gas flow is available. An undersized gas line can stress a tankless system and possibly reduce its lifespan, all Rinnai tankless water heaters are equipped with technology that safely ceases operation if they detect an inadequate gas flow. This innovative feature safeguards the unit from compromising performance and efficiency.

The tables below list the maximum length for both 1/2" and 3/4" gas lines when paired with Rinnai Tankless Water Heater models. Note: that Table 1 is intended for Natural Gas and Table 2 is intended for Low-Pressure Propane Gas supplies.

Table 1: Intended for Natural Gas
Rinnai Tankless Water Heater Models
Name Plate Ratings (BTU/H)
SCH 40 Metallic Pipe Size (Maximum Equivalent Length)
1/2 Inch
3/4 Inch
V53e 120,000 100' 450'
V65e, V65i 150,000 70' 300'
RUC80i, RU80i 152,000 70' 166'
RL75i, RL75e 180,000 50' 200'
V75i, V75e 180,000 50' 200'
RLX94i 192,000 40' 175'
RUC98i, RU98e 199,000 40' 175'
RL94i, RL94e 199,000 40' 175'
RUCS65i, RUS65e 130,000 100' 350'
RUCS75i, RUS75e 160,000 60' 250'
RU130i, RU130e 130,000 100' 350'
RU160i, RU160e, RUR160i, RUR160e 160,000 60' 250'
RU180i, RU180e 180,000 50' 200'
RU199i, RU199e, RUR199i, RUR199e 199,000 50' 175'
Rating is based on 1 Ci. Ft. Nat’l gas = 1,000 BTU
INTENDED USE: Initial Supply Pressure: 8.0" w.c. or greater; Inlet Pressure: <2 psi; Pressure Drop: 3.0" w.c.; Specific Gravity: 0.60
Source: NFPA 54/ ANSI Z223.1 National Fuel Gas Code

Table 2: Intended for (Low-Pressure) Propane Gas
Rinnai Tankless Water Heater Models
Name Plate Ratings (BTU/H)
SCH 40 Metallic Pipe Size (Maximum Equivalent Length)
1/2 Inch
3/4 Inch
V53e 120,000 50' 300'
V65e, V65i 150,000 30' 175'
RUC80i, RU80i 152,000 30' 175'
RL75i, RL75e 180,000 20' 125'
V75i, V75e 180,000 20' 125'
RLX94i 192,000 20' 100'
RUC98i, RU98e 199,000 20' 80'
RL94i, RL94e 199,000 20' 80'
RUCS65i, RUS65e 130,000 40' 200'
RUCS75i, RUS75e 160,000 30' 150'
RU130i, RU130e 130,000 40' 200'
RU160i, RU160e, RUR160i, RUR160e 160,000 30' 150'
RU180i, RU180e 180,000 20' 125'
RU199i, RU199e, RUR199i, RUR199e 199,000 20' 80'

INTENDED USE: Pipe Sizing Between Single- or Second-Stage
(Low-Pressure) Regulator and Appliance. Initial Pressure: 11.0" w.c; Pressure Drop: 0.5" w.c.; Specific Gravity: 1.50

Source: NFPA 54/ ANSI Z223.1 National Fuel Gas Code

Here are the steps needed to properly size your gas line:
Determine what type of gas is being used
Determine inlet pressure
Determine the allowed pressure drop
Determine what other types of gas appliances are sharing the gas line
Determine the maximum loads expected on the whole system as stated in the National Fuel Gas Code

NOTE: For complete information on gas sizing for Rinnai Tankless Water Heaters, consult the 'Operations and Installation Manual' that comes with your unit. Or, consult a licensed Rinnai installation professional who can help guide you through the process.

Rinnai offers a limited Field Conversion Program. Kits for converting gas tankless water heaters from natural gas to propane or vice versa are available for most models. Please have your installer or service provider call us at 1-800-621-9419 to find out if your model qualifies and to obtain a detailed step-by-step conversion instruction kit.

These kits are available directly from Rinnai. They will be shipped only after the installer or service provider has contacted Rinnai’s technical support services and consulted one of our technical specialists, to ensure the installer or service provider is qualified to perform the conversion. The Field Conversion Program is available for installed units where the gas type availability has changed. For safety, it’s not approved for use in conversion of non-sold inventory or mobile homes.

The maximum flow rate that our tankless hot water heaters can produce depends on temperature rise — the difference between the set temperature of the unit and that of the incoming groundwater. For instance, if you set the temperature of the unit to 120° F and the incoming groundwater temperature is 60° F, then the temperature rise is 60°F.

The lower the set temperature, and the higher the incoming groundwater temperature, the more hot water flow the unit can produce. If sized correctly for your application, the unit(s) won’t have a problem producing enough flow for all of your hot water needs.

Rinnai Tankless Water Heaters require 120 volts AC, 60 Hz and less than three amps.

Yes, a recirculation pump can be a great addition to your Rinnai tankless water heater system when continuous, on-demand hot water is needed. Plus, the modulating technology and minimum fire rating of the Rinnai tankless rack system enables it to maintain consistent temperature in a return line with limited waste. In that case, it only uses the energy necessary to keep the line heated when in use.

Tankless water heating recirculation works when a pump is activated by a switch or motion sensor. This is the most energy- and water-efficient way to operate a tankless water heater. It is also offers the most cost saving. Here’s how it works:

1. A switch or motion sensor located near each fixture (such as a shower or appliance) activates an energy-efficient circulation pump.
2. The circulation pump houses a temperature sensor and a check valve that prevents water from entering the return line. The pump moves ambient-temperature water sitting in the line back to the tankless water heater. The sensor lets the pump know when hot water has arrived at the farthest tap and shuts off the pump so energy isn’t wasted.

To learn more, check out an article by Rob Yagid in Fine Homebuilding Magazine, titled “Hot Water Recirculation Systems: How They Work.”

In order to have your tankless water heater installed, you’ll need to hire a qualified installation professional, who will help ensure safe installation and compliance with Rinnai warranty policies. We make it easy to find a licensed and trained pro. Click here to find one in your area.

Rinnai recommends you work with a licensed contractor trained to handle the plumbing, gas, electrical and venting aspects of installing a tankless water heater. This expert should be aware of all local and national codes. Having a non-licensed professional perform the installation can cause operational and performance issues and could negate the valuable Rinnai warranty. Click here to find a Rinnai independent dealer or advanced comfort expert in your area.

Instructional video for the MC-601/MC-91-2 Controller provides information on the LED Display, Controllers and Indicators
Some topics include those listed below and more...

Temperature setting under the priority function
Maintenance monitoring mode
Auxiliary functions of the controller such as changing from Fahrenheit to Celsius, control panel locking, etc.

MC195T Controller is used to control recirculation performance with Rinnai Tankless Water Heaters that have recirculation logic.
Note: Optional feature for luxury and some ultra RU series models. However, standard for the RUR Ultra Model series.

Topics Include:

Control panel details
Setting the clock
Adjusting the temperature
Timer overview and adjustment
Override features
Lock features
Silence beep


There are two types of periodic maintenance that your service technician should perform to keep your Rinnai tankless water heater in top shape. It’s important to note, the time in between necessary maintenance will depend on the water quality in your home.

1. The in-line screen filter should be checked periodically for debris and cleaned.
2. The unit should be flushed periodically to keep it free of scale and lime, which can shorten the water heater’s lifespan over time. This process should be completed by a professional installer. Please contact an installer near you.
Our How to video just in case you want to do some maintenance on your own.
Read the full article from Fine Home Building - Master in a Minute Video: Tankless Water-Heater Maintenance

For your safety, Rinnai tankless water heaters come with a maximum temperature default setting of 120℉ to help prevent scalding. However, by following these simple steps, you can increase the temperature to 140℉ if you choose.

Flow the six (6) step process to adjust your temperature:

1. Unplug the unit. For safety, always unplug any appliance before continuing.
2. Remove the front cover by removing the screws behind the plastic tabs on the 4 corners of the plate.
3. Locate the dip switches, which are located under the bottom right corner beneath the label.
4. Find dip switch number 6 and turn it on. You may use a small screwdriver if necessary.
5. Replace the front cover, securing it with the screws and reclip the plastic tabs.
6. Plug the unit back in.

Now you can increase the temperature to 140℉ on the front face of the unit.

Need more help? Click here for a helpful video detailing the process.

13-Step Tankless Water Heater Flushing Procedure

Over time, a tankless water heater may accumulate mineral build up which can erode the walls inside your tank's heating chamber. To properly maintain and clean your tankless water heater, it’s important to flush those mineral deposits at least once a year. Follow this simple process to ensure optimal tankless water heater performance and efficiency. Please read all of the instructions before beginning, as you’ll want to have all of the necessary supplies ready for the process.

Watch our Water Heater Flushing Procedure video on YouTube

5-Steps to cleaning your Rinnai Tankless Water Heater Inline Filter
Learn best practices on cleaning your filter from a Rinnai Trainer in this YouTube video


1) The pump may be in a mandatory dormant (inactive) state once the Rinnai Tankless Water Heater has detected that the desired temperature is acheived. 2) Confirm the push button is paired properly by pressing the push button. 3) The LED on the module flashes green to confirm that the push button is paired properly. If the LED does not flash green, your push button battery may need to be replaced, see your push button installation and owners manual for instructions on battery replacement.

Press and hold the Connect button on the module until the LED blinks RED and WHITE and then release the button. While the LED is flashing, QUICKLY press the Connect button 3 times. This will restore the module back to original factory settings as well as clear any stored WiFi information and button/sensor pairings.

Press and hold the Connect button on the WiFi Module until the LED flashes green, then release the Connect button. The module is now in pairing mode.

Refer to the owners manual of the on-demand accessory.

Yes, you still have hot water. The Rinnai Tankless Water Heater should always respond to a hot water fixture being open regardless of the WiFi module status.

Your Rinnai Tankless Water Heater is NOT affected. You will still have hot water. The recirculation schedule will continue as previously saved. The Rinnai Central™ mobile app will not have access to the module untill internet connectivity is restored. However,'On Demand' accessories will continue to function. Your module will automatically reconnect when the internet returns.

No. Setting up on-demand recirculation accessories does not require the homeowner’s Wi-Fi network. These accessories communicate directly with the module attached to the Rinnai Tankless Water Heater.

Each WiFi module can easily support 5 or more paired on-demand recirculation accessories.

If your Rinnai Tankless Water Heater has recirculation capability, you can activate recirculation though the use of you WiFi Module. The module can be wirelessly paired with motion sensors or push buttons. The Rinnai Central app can also communicate with the module to allow recirculation scheduling. {click link to LP, and link PDF files for sensors and buttons}

You have about five minutes to complete the pairing process before the module times out. If the pairing mode times out, press and hold the Connect button again on the module until the LED turns to a flashing GREEN, then release the button to put the module into accessory pairing mode.

When pairing multiple on-demand accessories, you must re-enter pairing mode to pair each accessory.

Yes, because push buttons and motion sensors are paired to the module. If the module is swapped, the on-demand accessory (push button, motion sensor, etc.) must be factory reset and paired to the new module.

Power Cycling shuts down the power to the module and then restarts power. To cycle power on the module, insert a small pin into the "RESET" opening. When successful the LED will turn off. Remove the pin to restart the unit.

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