I am no expert here, and have no experience using a UPS to operate an appliance other than my refrigerator. In my case it is not connected to operate in a power outage, more to clean up the sine and protect against power dips and surges and theoretically extend the live of the compressor. I also have them connected to my OLED Television and many other electronics in my house. In an actual outage all you hear is beeping out of every room in the house lol.

At any rate a Tankless heater is pretty demanding on electrical current and it is unlikely you will find anything at Best Buy that will do what your looking for. Is the heater supplying hot water to the entire home or is localized to one bathroom? Is it 110v or 220v? Based on the link you provided I am going to assume it is 110 and localized. You can connect that, however how long it will last depends upon current draw and how much use and be prepared to change the batteries often if you drain them on a regular basis. The one in the link you provided will likely not last more than a few minutes. If you seriously want to be able to get any use out of It I would buy the largest (capacity wise) I could afford. To get anywhere close to where you want to be I estimate you will need to spend upwards of $500.00. I am guessing somewhere in the 3000va range? I am interested if anyone else knows of a consumer grade solution to your inquiry.

Thanks. The whole house tank itself runs on gas. The electricity Is only needed for the controller. When I google, all the sites recommend a Hugo as a permanent dedicated solution.. Rinnai even lists it on their site.

https://www.rinnai.us/hugo-x-1-battery-backup-system

i was wondering if there is something cheaper and portable. Thanks

Oh, that certainly changes everything. In that case the one you linked should be ok. I personally would go bigger maybe 950va just to give yourself a lot of head room in the capacity area. IMO in the case of a UPS bigger is better. The igniter does not use that much power and does not run continuously so you should be fine. Although I am not certain how much power the controller uses, hence the extra capacity.

Just a peek at Provantage's latest flyer reveals four brands: HPE, Tripp Lite, APC, and CyberPower. My flock of UPS are APC. What you need to do is find out the current draw of your controller, then multiply by the line voltage to get watts. Then multiply by the power outage time in hours you want to plan for to yield watt-hours. Then buy a unit capable of that duration. The manufacturers should have such data on their web sites.

Thanks. I was thrown off that the UPS’s battery outlets can’t handle the heavy load of a .... laser printer. I don’t understand what kind of load items use. I thought the heavy load items are things like blow dryers and irons, not a printer. So it was hard to know where this water heater controller fit into that scheme.

@kevinande I considered a larger one but then they start looking like a CPU tower and weight 25 pounds. This was the largest capacity at Best Buy that looked portable to me (14 pounds?) I picked Best Buy since it’s easy to return if needed; we have one in town.

@kaseki thanks for that info and the tip that manufacturer should have the data on their website. Do you like APC? When I did my little research it seemed like CyberPower got better ratings but I think APC tends to be a little cheaper.

Many of mine were purchased before I knew of CyberPower. In more recent cases the configuration or features determined the selection. There can also be delivery time and price factors.

At the moment, I have 6 operational: 3 for 3 PCs, 1 for my networking rack, two for two ONTs (fiberoptic modems, essentially).

These only have to work until the main motor generator fires up. None of these APC supplies are of the continuous sine wave type. I have not yet needed them because the motor generator is fairly clean as is the utility power.

As far as I can recall, only one unit eventually failed, a 1500W. The repair has been published, but required microelectronic tools to deal with, and that would have been a bigger hassle than just buying a newer model replacement. The replacement is at my feet right now keeping me posted on that exciting parameter -- local line voltage.

Most inexpensive home UPS Backups produce a Square wave output when AC is lost... they work just fine with household electronics, including TVs and Computers.

"Unless you run some sensitive scientific, medical, or audio equipment you don't really need" a pure sine wave.

Thanks again everyone for your help. I chatted with Navien again an they say they do no recommend any specific model but that I’d need one that used 110-120 AC and 2A (4A with an external pump). My pump is internal.

For comparison, I checked laser printers. Looks like some need 4A to heat up and start printing.

For comparison, the Hugo says it provides:

—A 500VA/ 350W uninterrupted power supply (UPS)(

(the specs on Amazon say it’s a Pure Sine Wave. Navien didn’t mention that)

Here’s info from the RInnai website.

https://www.rinnai.us/hugo-x-1-battery-backup-system

I’m feeling stumped on what to do. This morning I was wondering about logistics. My heater is mounted outside and around to the side of the house. If we have a power outrage, how fun will it be to walk around the house to plug in the UPS, take a shower, go back out and disconnect? What if this happens in the rain? I guess I can’t use my portable one. Maybe I’m getting lazy here. Thoughts?

First, for best operation, the UPS should be continuously operated in line with the heater control unit. This could be done with the UPS indoors.

Second, 2A at 120 Vac is 240W. This is easy for even modest UPS sizes.

Third, to operate for an hour requires 240 W-hr battery capacity (to some level of charge). To operate for a day requires 5.8 kW-hr capacity. Now we are getting into the big battery range of performance.

Example: Modest capacity UPS in the 1500 VA or less range typically use one to two batteries such as the Duracell 12-8F2. One of these will supply 12 volts for 8 ampere-hours, or about 100 W-hrs. It is about 50 cu. in. in volume. To supply 5.8 kW-hrs, one would need (in lead acid chemistry) a 58X larger battery. Several car batteries might be enough.

So what is your expected power outage time? Do you want to wire up a UPS with a manual transfer switch so that you can power the heater's controls only for brief times, thereby extending UPS operation time? (You will have to determine that the UPS will provide ac power when charged but line power is off. I once had one of mine charged but not connected and when I tried to use it as a power supply it wouldn't cooperate. Power stations such as are used for remote use of power tools would not have that issue.)

Bottom line: determine what you want this backup device to actually do and a means can be found to do it.

Power outages are rare (knock on wood) and i live in a mild climate. My thought had been to have a portable UPS that I keep inside the house and on the rare situation where the power outage coincides with the need for someone to shower, I could walk the unit outside to power the controller. Then, a few mins later, (10-15?) disconnect it and bring it inside. My thought was to start with this and if it’s not enough, I could upgrade to the Hugo. (?) But reading that disclaimer on the UPS (that the battery backup plugs can’t be used for laser printers, etc) made me worried that there may be more involved than I thought. Then I started wondering if I really want to be going outside twice to connect and disconnect a unit.

FWIW, the one I bought is 950VA with max wattage of 510. Best Buy has a slightly larger one (1000 VA/ 530 Watts) for $20 more. The larger 1500VA ones start to get heavy (25 pounds) and the size of a CPU tower, which then creates more of a storage issue and becomes heavier to lug around.

Thanks for your help.

"One of these will supply 12 volts for 8 ampere-hours, or about 100 W-hrs."

???

@Stax: are you questioning the result based on the voltage curve with power drain, or just asking about the calculation? If the latter, then 12V x 8 A-hrs = 96 VA-hrs. I assumed a resistive load (1 VA = 1 W) and rounded up for the purpose of editorial convenience, but the value of the rated current lifetime is based on some current draw rate and voltage "cut-off" so the answer will always be somewhat squishy. Note that the battery case specifies the ampere-hours.

Hi! @girl_wonder, Old thread but wondering what you needed up doing. I also have a Navien and never bothered with a back up, but thinking about it as winter starts. I had the exact idea as you and am trying to keep it cheap. How much is a shower worth and how often is my power out more than a few hours ..not often! just want to be able to plug it in for a shower or wash my face in a pinch. I wouldn't leave it plugged in. I saw the one with 950 W and wondered if it's enough. Heck, I'd try the 650, there are only 2 of us. We do have a portable generator, but I'm scared of it messing up the control board of the tankless. Did you keep the 950 and did you use it at all yet?? Thanks! Mine is in the basement, so easy enough to plug in and out.

If you want to take a shower during a power outage -- which seems like an odd priority -- go with a Tesla Powerwall installation. It will cost you probably 10 times what the tankless, electric water heater cost, but it will do the job. A UPS or other electronic gadget will do diddly squat. Or you could have a natural gas tankless, and then you only need a trivial amount of power -- such as a UPS can provide -- to run the electronics of the water heater.

@kudzu9

If you had read any of the follow up comments, it is mentioned that the OP has a natural gas tankless water heater.

kevinande-

I was responding to the latest comment and made the assumption, possibly wrong, that the poster had an electric tankless. But point taken. Thanks.

@Cindy B sorry for the delay. Yeah, I kept the 950 and figured I could use it for other things, if needed. As luck would have it, we haven't lost power again. So maybe that's a good reason to have it, as a good luck charm. You know, how on the days you bring your umbrella, it never rains. ;) Good luck!

I have a Navien NPE-240S2. I put my Fluke meter on the AC and here is what I measured.

• Standby mode: 0.06A
• DHW-Wait: 0.180A
• Active: 0.300A (1 faucet)
• Active: 0.400A (1 shower)
• Active: 0.600A (1 shower + 1 faucet, it's not exactly linear)

Those are eyeballed averages from a recorded trend line on the fluke. The power consumption fluctuates quite a bit.

Clearly, the active power consumption depends on how much hot water demand you have.

Let's say I want 4 showers at 15 minutes per day, plus 1 faucet for 6 minutes 10 times per day. The DHW-Wait mode lasts for about 3 minute after hot water demand ends, then it goes into standby. That would be (in VA-hr):

• 4 * 0.25hr * 124V * 0.5A (rounded up a little) + 4* 0.05hr * 124V * 0.18A = 67 VA-hr
• 10 * 0.10hr * 124V * 0.4A + 10 * 0.05hr * 124V * 0.18A = 61 VA-hr
• 1 * 22hr * 124V * 0.06A = 164 VA-hr
• Daily total: 292 VA-hr

So a 1500VA battery would last for 5 days. YMMV.

I'll hook one up and unplug the utility and see how it does! I'm sure I've missed different power cycling on the Navien that will result in higher power, such as if it's trying to anticipate DHW usage and automatically goes out of standby now and then. I also observed that the power-on cycle uses a fair bit of power. Also, the numbers I used were eye-balled averages. There were some high spikes (about 1A), but also some lows.

PS: I think one would be limited mostly by the UPS's inverter efficiency. Some UPS models have a "max runtime" in the 10 minutes - 1 hour range, as they are always producing at least 50W or more. The inverter efficiency also drops (maybe down to 70% or less) for low loads. Actually, it might have more to do with lead-acid batteries than the inverter, but in any case, short-life UPS are common.

Generally, UPS's were not designed for this type of application. They were intended to provide temporary power from a fraction of second to usually less than an hour - time enough to switch to generator or do a safe shutdown of servers. They aren't going to run for hours - even with a low draw situation.

@Marc thanks for taking the time to make the measurements and share them.

@Jake The Wonderdog thanks for your feedback.

I don't need anything that's going to run for a long time. I had a problem a while ago where we had a power outage for several hours and I wanted to get a quick shower before heading out. It only needs to run the controller. The tank itself is gas. So we'll see how this goes and/or if this issue even comes up again. Thanks again for your help.

Hi there, I have a navien tankless as well in the Bay area. We had a power outage. and I ran down to Autozone and got a Green Fuel 500w Power inverter that hooks up to my car battery. I ran a short extension cord to my heater (in garage) and me and my family all took showers (4 people). It worked out great. It is a MSW inverter that was $66. I do have a Optima Deep cycle battery in my truck but I looked up the calculation online estimated for a 300w draw and it should easily should have lasted 5+ hours continuously. I had the Navien plugged in for an hour and it worked like a champ. I think i may just order a Bestek Pure sine 500w off Amazon for the same price, for the cost it is cheap insurance. No noticeable effect on my car battery.

I like @Ruben C's solution as a good alternative to computer UPS, given certain implied requirements can be met by the "truck" and the premises and one's willingness to set up the configuration. In 10-inches of snow, it might be annoying to deploy.

Upon re-reading this thread, I can see that one option was missed -- job-site portable power tool supplies, such as (e.g.) Milwaukee make: https://www.milwaukeetool.com/Products/Batteries-and-Chargers/M18-Batteries-and-Chargers/M18-Chargers_Power-Supply/2845-20 (choosing a tool brand at almost random). These are likely somewhat heavy (M-18 is 28 pounds), but designed to operate in adverse conditions.

@Ruben C, what a great solution. glad it worked and thanks for posting. i don’t own a truck but a Prius. Do you think would work? i assume it would only draw on the ”regular” car battery not the big battery pack (though it makes me wonder if folks over on Prius Char have heard of anyone taping into their big battery packs.)

i also live in wildfire county and bought one of these batteries for my Go Bag. You can plug into it.

https://www.amazon.com/DBPOWER-Jump-Starter-Red/dp/B077HY7SFJ/ref=sr_1_14?ie=UTF8&qid=1543161259&sr=8-14&keywords=battery+charger+for+cars&redirectFromSmile=1

Do you think this would work? i’m not sure how much electricity these gas-powered water heaters use. just fot the controller? i don’t need it to run an hour.

@kaseki thanks for that great idea too. i didn’t know thise things existed.

To follow up on this thread, I went with the Hugo battery backup, which is designed to be a long-running backup. it also includes a water flow switch that can turn the inverter off when there's no hot water demand. They claim it can run for 14 hours or 7 days with the on-demand switch.

It is in a weather resistant case, so it could be installed outdoors. I have mine in the utility closet up on some bricks. It is also wall mountable.

https://a.co/d/cnmh79P

@Marc, thanks. I had looked into it but was scared off by the price lol. Glad it's working for you.

Can you test it by cut off power source to the tank and see how long it will last with 950VA from best buy? Test it with usage like a normal shower. tx

I have read these comments and see no one has mentioned what I consider to be the most important. At least for me. Navien has a freeze prevention system until the electric power goes out. My system heats water with propane so electricity is only for freeze prevention and ignition as I understand it. It is outside (requirement of local code) so freeze protection is a priority when we lose power in the winter and temps drop. I will shop for the minimum.

@HU-975008282

Yes, you are mostly correct. Power is needed for the controls, ignition, fans and freeze prevention. You should really check your code though. I would encourage everyone not to install plumbing outside - including gas tankless heaters. Even if your area hasn't frozen in the past. It's just asking for trouble (Texas, looking at you).

One thing I did not see anyone mention is the ability of the UPS to auto power on after the batter is discarged during a power outage. CyberPower does not do this. APC says all of their units do.

Heya Scott,

Im not an expert on all of this, but here's my 2cents. All UPS units should just power back on to last state (on or off) once the power returns. I checked the Navien specs, its draw is 200w max. If you got a 700w battery backup, that should give you about an hour of runtime for your tankless. This would be if the battery was plugged inline between the wall and your water heater. Im an IT guy and size batteries for telecom equipment.

What will happen over time however, is the battery backup uses lead acid batteries sits and waits for power outages to occur. Its in a constant charging state, and after about 3 years or so the batereis need to be replaced. As you get closer to replacement, the runtime of the backup unit shortens, so 1 hr at 200w is an optimal setting. Also, i think 200w is a max draw number, Im not sure what its volt amp draw is, but I dont think it is much lower. I do know that when running the hot water, the Navien has to power a recirculation valve actuator to direct the hot water through the pipes, I would think that wold be using more electricity rather than the electronics.

Once the power goes out, your one hour clock starts ticking from that point with a consumer battery backup. You could turn off the battery backup and power it up when you want hot water to extend your window. It will beep while the power is out (alarm, which you could turn off).

I have a car battery inverter that I use to power my Tankless, but for a while considered getting a small generator that would run hot water and the refrigerator for short cycles. If I had to throw out all the fridge and freezer food it would more than pay for the generator, but historically we dont get long outages (bay area peninsula). so far..... My new concern is the fridge food is considered safe for up to 4 hours, and the freezer 24, so thats become my new worry for backup.

Thx,

Ruben

@rubenc,

I agree one would think that a UPS would return to last state however, I did a lot of research and among the smaller UPS sellers only APC even claims to do this. I have one ordered for a CoolToys TV test to verify.

The reason I posted this is the 1000VA CyberPower UPS I had protecting my Noritz tankless did not return to a powered on state for the battery protected outlets. CyberPower confirmed this to be the correct operating state »to protect the unit ». It was very annoying to wake up to cold water.

I had a second 950VA CyberPower backing up my Universal Devices eisy home controller. so not only was the shower cold, the house was cold and dark.

Tripp-Lite at the higher end also does this, but be careful the website says »network » and above which is not true.