How Do I Use This Tankless Water Heater?

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Barnibus.convert

New member
Joined
Jun 20, 2021
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3
Location
Oregon
I'm converting a school bus and learning everything as I go. I'm about to start gathering the components needed for my power system. I'm getting it all figured out and would honestly be doing just fine were it not for the tankless water heater I bought...

A few months ago I bought an electric iHeat Tankless Water Heater, 16Kw (why do I feel dread even typing that?). From the research I did at the time I knew it would pose a challenge, but I'm fine with challenges and the manufacturer said this particular model, while intended for small houses or apartments, works well in small boats, RV's, and so on. In fact in doing research, it seemed quite a few others used them in their RV's, 5th wheels, and one guy even said he had one in his camper (seems like overkill but whatevs).

I'm not going to bother taking everybody on my hellish research journey into power systems that's gone on now for an unknown number of days (what month is this?), and instead I'll just cut to the chase: I know how to get the required volts from 50A shore power (240v), I get now how appliances use watts (did you know kWh's was a thing?), now I'm all hung up on amps. This particular water heater requires its own dedicated 70A double-pole circuit breaker and that's really where I'm hung up (its a 66A appliance). I get it; 50A is 50A and that's all you can get from shore power. The confusion really comes in when you hear others talk about their RV air conditioners that draw a whopping 150 amps, but somehow they figured it all out. Or the guy who uses a pizza oven that draws over 100 amps and all he has to do is flip a switch and his solar panels somehow pick up the slack. The longest I'd ever use my water heater (it's a manual power switch you turn on and off yourself when you need it) is for a 15-minute shower, which by my calculations would use 4kw and 16.67A - hardly a mammoth when compared to an air conditioner or even pizza oven. I also wouldn't need it on its highest temperature setting, which is what would bump it up to 16kW, so a 15-minute shower would actually take less power than my calculations show.

So what's the piece of the puzzle I'm missing?

To give everyone an idea of what I'm working with so far in my power system; I've got three 325W mono solar panels mounted on my roof (they're supposed to be really good and super efficient), plan to get three 105AH deep cycle batteries (maybe four), Renogy said their 2000W Pure Sine Inverter would work well with all that. Oh and I've got a 3500W, 4000W surge generator. Still have yet to collect everything else but I've got a good idea of what I specifically need. I've kinda got my heart set on an electric tankless water heater rather than a propane one for a few good reasons, for the record.
 

Lou Schneider

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Joined
Mar 14, 2005
Posts
10,954
Hi Barnibus, welcome to The RV Forum!

The part you're missing is amperage is only half of the power formula, which is Power (Watts) = Voltage x Current (amps).

When you hear people talking about using 100 -150 amps to run something, that's at a low voltage like what a battery supplies to the input of an inverter. 12 volts x 100 amps = 1200 watts. It's the same amount of power as 120 volts x 10 amps, or 240 volts x 5 amps.

Unfortunately, at 16,000 watts (240 volts x 66 amps) your tankless water heater needs way too much power to use in an RV. The only RV practical tankless water heaters are propane fired because propane can produce much more heat than what is available from the RV's electricity.
 

8Muddypaws

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Jul 18, 2014
Posts
3,351
Location
California
A 50A RV pedestal, when wired correctly, delivers a full 100A at 240Volts.

Talk to a licensed electrician. I know from experience that 240Volts hurts.

That I learned that firsthand at the tender age of 16 is part of the reason I didn't join the family business and become an electrical contractor.
 

solarman

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Joined
Feb 8, 2018
Posts
459
Location
Texas
A 50A RV pedestal, when wired correctly, delivers a full 100A at 240Volts.

Talk to a licensed electrician. I know from experience that 240Volts hurts.

That I learned that firsthand at the tender age of 16 is part of the reason I didn't join the family business and become an electrical contractor.
how does a 50A 250V pedestal, fused with a 50A breaker provide 100 A at at 240V ?
I think you meant to say two circuits of 120V at 50A each.
 

Barnibus.convert

New member
Joined
Jun 20, 2021
Posts
3
Location
Oregon
Hi Barnibus, welcome to The RV Forum!

The part you're missing is amperage is only half of the power formula, which is Power (Watts) = Voltage x Current (amps).

When you hear people talking about using 100 -150 amps to run something, that's at a low voltage like what a battery supplies to the input of an inverter. 12 volts x 100 amps = 1200 watts. It's the same amount of power as 120 volts x 10 amps, or 240 volts x 5 amps.

Unfortunately, at 16,000 watts (240 volts x 66 amps) your tankless water heater needs way too much power to use in an RV. The only RV practical tankless water heaters are propane fired because propane can produce much more heat than what is available from the RV's electricity.
Thank you for your response! Yes, I ended up figuring all this out (for the most part) around 2-3am the morning after I posted this. Goodness, it was a nightmare. I was glad to read your post though, which confirmed what I had basically figured out later, and even added further clarification. Thank you for your help! :D
 
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