Plumbing, Water Heaters

Operating a Tankless Gas Water Heater Without Electricity

navien tankless water heater2 lg

When the power goes out, hot water is one of the essential luxuries you risk losing. If you use a tankless gas water heater to provide your home with hot water, you may wonder if you’ll have hot water in the event the power goes out. 

So, will a tankless gas water heater work without electricity? No, a tankless gas water heater still requires some electricity to operate. Tankless gas water heaters have an internal PC board, electronic ignition, and an electronic thermostat that requires electricity. These components will not operate without a power source, preventing the tankless water heater from producing hot water.

Tankless water heaters have a built-in PC board and digital remote that need electricity to operate the water heater. These components sense the flow of water and turn on the burner to generate hot water on demand.

Tankless water heaters also have a direct electric ignition that uses 120v power that lights the burners as hot water is needed. If the power is out, the ignition system will not operate.

While your gas-powered tankless water heater does need electricity to work, that electricity doesn’t have to come from your power outlet. If you experience a power outage, the best option is a portable generator that can power the tankless water heater and other household appliances and mechanicals such as the heating and cooling system, refrigerator, stove, lights, etc.

If a backup generator is not viable, you can temporarily install a battery backup system to power the tankless water heater.

Concerned about installing a water heater outside? We address this concern in Can Water Heaters Be Installed Outside: What You Should Know.

Why gas-powered tankless water heaters need electricity

All tankless water heaters require electricity to function properly ‒ even gas-powered models. Electric heaters require electricity to heat the water, but both need electricity to power their electronic control system, ignition system, and remote thermostats. 

The thermostat communicates to the control panel to operate the burners and ignition. The heater will shut down and stop heating water when the power outage occurs.

Fortunately, there’s an easy and affordable way to keep your water heater operational when the power goes out. 

How to keep your tankless water heater running during a power outage

The best way to prevent hot water loss during power outages is by installing a battery backup system. These relatively inexpensive devices will connect to your tankless water heater and provide emergency electric power whenever your primary source of electricity goes down. 

They don’t pack the same punch as a generator, but that’s the point ‒ it’s a cost-effective way to provide electricity to gas-powered devices that need it. A gas-powered tankless water heater is a perfect example of a device requiring a battery backup system. Without it, you lose the ability to do many things essential to living a civilized life. 

For information on protecting a water heater from freezing, see our article Maintaining Tankless Water Heaters in Freezing Temperatures.

HUGO Battery Backup for Tankless Water Heaters

While many backup battery systems may be compatible with tankless water heaters, the HUGO Battery Backup for Tankless Water Heaters (available on Amazon) is the only model designed explicitly for use with tankless water heaters. Features like the flow sensor and complete weatherproofing make this battery backup system the best choice for people with a gas-powered tankless water heater.

Water heater specificity aside, the HUGO is honestly a solid overall battery backup system. It has a standard power rating of 350W/500VA, making it compatible with almost all gas appliances. The pure sine wave output also ensures a longer device lifespan and more efficient power usage ‒ which translates to a lower energy bill. 

HUGO Battery Backup for Tankless Water Heaters and Gas Appliances (Standard Flow Sensor)
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03/11/2024 05:19 am GMT

It’s also solar capable, which is a pretty big deal, in my opinion. Many backup battery systems need to charge up using the home’s primary power source ‒ which can be a problem when the primary power source is out for an extended time.

Because the HUGO is solar capable, you can connect it to a solar panel and charge it when you don’t have power. This is especially useful during long outages, as you can recharge your backup battery if it depletes its energy stores. 

To help you understand why the HUGO battery backup system works so well with tankless water heaters, I’ve listed a few defining features and explained how they could benefit your tankless unit. 

Flow sensor 

The built-in flow sensor is one of the most helpful features of the HUGO Battery Backup for Tankless Water Heaters. Although the HUGO has a decent battery that can handle up to 13 hours of continuous use, conserving that energy should still be a top priority ‒ especially when dealing with outages that last more than a day. 

The flow sensor on the HUGO will help immensely with conserving energy. It will only activate and transfer energy to your water heater if it detects water flow. If no flow is present, the HUGO will remain in standby mode and use almost no energy. 

This feature makes the HUGO especially useful in locations where extended outages are somewhat common. While using another model without a flow sensor is viable, having the extra energy savings from a flow sensor might be the difference between a hot and cold shower amid a snowstorm or other outage-causing weather events. 

Automatic switch over

In addition to being effective, the HUGO Battery Backup for Tankless Water Heaters is also convenient and user-friendly. The device can detect when your primary power supply is out and will shift your water heater to battery power within 8 milliseconds if an outage occurs. It will also automatically switch your heater back to your main power supply once it has been restored. 

While this feature might seem minor, it’s one less thing you have to worry about when the lights suddenly go out. 

Indoor/Outdoor installation

While installing your backup battery system indoors to protect from freeze damage is preferred, it isn’t possible in all circumstances. 

Fortunately, the HUGO is fully equipped and graded for outdoor use in all kinds of weather. 

  • The exterior metal housing is incredibly thick. Sleet, hail, and other heavy precipitation will not dent the casing or affect the interior. 
  • The unit has antifreeze assist technology, which will protect your hot water source in frigid temperatures ‒ which is the exact time having hot water is most important. 
  • The HUGO also has an IP54 grade, certifying it for protection in different weather scenarios. An IP54 grade also specifically mentions total liquid protection ‒ so there’s zero chance rain gets in and damages internal components. 

Temporary or permanent mounting options 

Depending on your life situation, you might not want to install your battery backup system with a permanent, hard-to-remove mount. 

Maybe you’re going to be moving in a few months. Maybe you’ll be remodeling and will need to relocate your water heater. Whatever the case may be, the HUGO gives you flexibility in this area, as it offers both portable and permanent mounting options. 

Additional features 

While the features specifically designed for water heaters are the HUGO highlight, it has some other useful features worth mentioning. 

  • It has a built-in fuse to protect from circuit board overloads. This also protects your downstream hot water devices from power surge damage. 
  • A non-spill battery makes it even safer to place this device inside your home. 
  • You don’t have to use the HUGO with a tankless water heater. It is perfectly compatible with most other gas appliances too. 

The downsides 

While it does a great job for the price, the HUGO is not a perfect backup battery system. You should know about a few flaws before making a purchase decision. 

First, the manufacturers made it so the flow sensor must be operational for the device to work. If you want to use the HUGO as a backup for something that isn’t a tankless water heater, you’ll need to open it up and disconnect the flow meter plug. This is a relatively simple process, but it can cause unexpected problems if you don’t know to do this. 

Next, the device isn’t exactly quiet. While the noise when it’s operational isn’t overwhelming, it can get bothersome if you prefer a quiet home. Fortunately, the advanced weatherproofing on this machine makes putting it outside a safe bet. 

Finally, the HUGO makes a repetitive beeping noise when the power initially goes out. This beeping is supposed to signal that the power is out and that the heater’s power supply is switching to the backup battery system. However, after the first few beeps, it gets pretty annoying, especially if your water heater is near one of your living spaces. Fortunately, the noise only lasts about ten minutes before shutting off. 

Installing the HUGO Battery Backup System

Installing the HUGO Battery Backup is relatively easy but requires some minor plumbing work. If you are uncomfortable with plumbing work, you should call a licensed plumber to assist with installing your HUGO Battery Backup system.

Step 1: Remove the battery from inside the HUGO case

The HUGO weighs 43 pounds in total. The interior battery weighs approximately 30 pounds. Remove the interior battery to lessen the weight when initially hanging the HUGO battery backup system. To remove the battery:

  1. Remove the four screws holding the interior L-shaped bracket in place.
  2. Using the quick disconnect, disconnect the wiring to the battery.
  3. Remove the battery from the cabinet.

Step 2: Install the mounting brackets

The HUGO has four mounting brackets that you must install on the back of the cabinet. When installing the mounting brackets, be sure the keyholes are at the bottom of the bracket. Secure the brackets to the cabinet with the provided screws and washers. This will allow you to easily set the wall screws and hang the HUGO. You must install all four brackets to ensure the stability of the unit.

Step 3: Hang the HUGO cabinet

To hang the cabinet, you’ll need to set one screw initially. Setting the screws will depend on the mounting surface. In the video above, the unit is installed on a wood surface with wood screws. If mounting the cabinet outside, you’ll need to use mounting hardware designed for the exterior wall material. Anchors will be needed for masonry installation.

Hang the HUGO cabinet on the initial screw. Level the unit and install the remaining three screws. Tighten to the wall surface. Apply sealant over the screws if needed.

Step 4: Reinstall the battery

Now that the cabinet is installed, it’s time to reinstall the battery inside the cabinet. Install the L-shaped bracket and four mounting screws. Do not connect the cables yet. We will do this later.

Step 5: Install the flow switch

This is where you may need a licensed plumber. This is a relatively easy task, but you shouldn’t do this if you aren’t sure about what to do or do not own the correct tools to do the job.

  1. Power down the tankless water heater.
  2. Cut off the cold water supply to the tankless water heater.
  3. Drain off the water supply by opening the water supply at a nearby sink.
  4. You’ll need to install the flow switch on the cold water line coming into the water heater.
  5. Apply Teflon tape on the threaded ends of the flow switch and install connections to the flow switch that matches the plumbing supply piping. The video shows installing the fittings for Pex piping, which is common in most homes. Pex does require a special crimping tool. Do not try to crimp the fittings with any other tools to damage the fittings and leak.
  6. Install the flow switch with the flow direction arrow pointing towards the water heater. This is very important as the switch will only work in this direction.
  7. Be sure the flat portion of the flow switch is facing down.

Step 6: Check for leaks

Turn on the water supply and check for active leaks on the plumbing connections. If no leaks are present, you can proceed to the next step. Turn off the water supply to repair the plumbing connections if leaks are present.

Step 7: Plug in the flow switch

Now it’s time to plug in the flow switch. To do so, locate the side panel on the cabinet. Remove the four screws securing the cover and take out the power cord. Locate the port for the flow switch and plug it in. This will only fit in one direction.

Step 8: Plug in the tankless water heater

Inside the side panel, you’ll see an outlet to plug the water heater. Once the water heater has been plugged in, reinstall the side panel. The gasket on the side of the panel seals the compartment from dust and moisture.

Step 9: Connect the battery cables

Inside the main cabinet door, reconnect the battery and quickly connect cables. Plug the unit into the wall outlet and turn the toggle switch on.

Step 10: Turn the water heater on

The installation of your HUGO battery backup system is complete. Power your water heater up and verify it is working correctly.

HUGO Battery Backup System Check

Before locking the HUGO cabinet door, do a check system check. You can do this by looking at the indicator lights inside the cabinet. The first green indicator light will be on if the power is on.

You can simulate a power failure by unplugging the HUGO system from the outlet. When this happens, the second green light will indicate the system is operating on battery power. Confirm the water heater is on and producing hot water.

Upon completing simulation testing, plug the HUGO system back into the outlet, close, and secure the cabinet door. Congratulations, you’ve successfully installed your HUGO Battery Backup system.

Another feature the Hugo backup battery offers is the ability to integrate solar panels to charge the battery. This will allow you the option to provide power to run your gas water heater for lengthy periods in the event of a power outage.

The backup battery can carry the water heater for about seven days of regular operation. Having solar panels added to the Hugo battery backup can provide unlimited charging and runtime when the power is out.


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.