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I live in an RV and am trying to install an electric tankless water heater by myself. It says it requires 2 double pole 30 amp breakers which is not really an option for me, the manual says the heater only draws 45 amps.

My landlord who also builds RV resorts for a living told me to use #6 wire and a 50 amp male plug and plug it into the 50 amp spot on my terminal. My RV is plugged into the 30 amp and nothing is using the 50 amp plug so the water heater would have the 50 amp to itself.

I have bought the wire and plug and installed them on my water heater. I have also already hooked up the plumbing I just haven't plugged it in yet. Is this going to work or will it burn up my unit? As far as solutions, this was a solution I need to figure out how to get this thing running so I can have hot water. I'm broke so spending a lot of money is out or I would have paid a professional to come and install it.

Also, does anyone know if I can have the unit laying on its back instead of mounting it upright?

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    Your landlord is not an electrician. Installing anything against what the install instructions say is a big no no. Two double pole breakers means four hot wires, one 50 amp plug means two hot wires, so what are you doing with the other two hots?.
    – crip659
    Commented Feb 10, 2023 at 17:11
  • I used splicers
    – RandaNae
    Commented Feb 10, 2023 at 17:17
  • For the answer to the "can I have the unit lying on its back" question consult the installation manual. We use small point of use tanked heaters on our boat.
    – RoyC
    Commented Feb 11, 2023 at 11:13

2 Answers 2

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This is wrong in many ways:

  • Instructions are based on UL/ETL/etc. determination of the safe way to power and install the device. In particular, when a large power device moves from 1 circuit to 2 circuits that is almost always based on a truly large current draw, because a single circuit would be cheaper (one breaker instead of two, one set of wires instead of two, etc.). So by not following the instructions you are installing it incorrectly, which means that if you ever have an electrical-related fire, even if it is not directly related to this installation, your insurance may refuse to pay based on things being improperly installed.

  • If you use 45A to run your electric water heater then that leaves only 5A for everything else on the 50A circuit. If you use 10A - 20A at the same time then you will be overloading the wires. HVAC, cooktop/oven, etc. could all easily lead to an overload. Depending on the size/time of the overload, that might trip the 50A main breaker (a nuisance every time it happens, but repeated trips are not a good thing for the breaker itself) or it might not (there is some wiggle room in breaker design which allows for short-term moderate overloads) which would not be good for the wiring.

  • Most water heaters are not designed for cord/plug connection. They are designed for hardwired connection. This actually makes sense - if the water is connected permanently, why not the electricity? If you are referring to the 50A receptacle in an RV park, where are you connecting the rest of the electricity for your RV? And if you are referring to a 50A receptacle inside your RV, that makes no sense at all. Even when there is an option, I almost always prefer hardwired connections as that removes a common source of problems.

  • On-demand electric water heating is simply not a good fit for many homes due to the high current draw. Or rather super huge current draw. Far better is one of:

    • Natural gas or propane heating - that may not be available or practical or safe, but if it is available and practical and safe (i.e., designed for RV installation and use) then it is worth considering.
    • Tanked electric heating - This is the usual solution. You probably don't have room for a 50 gallon tank. But if you can make room for a 20 gallon tank, that would work very well. For example, in a quick search I found that Rheem has a line of 6 - 30 gallon electric heaters that use 2000W and install on a 25A 120V circuit.
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    Gotta agree and support manaseeshkatz answer. Electric tankless WHs are major power hogs. If you wanted a small one next to say a kitchen sink or bathroom sink, fine, their only about 1,200-1,400 watts they are called "point of use" water heaters. again, agreeing with manasee... get small tank type water heater that would be much more compatible with the electrical supply for an RV. Commented Feb 10, 2023 at 18:57
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That dog won't hunt.

First, it's not big enough for your needs.

If it were big enough for your needs, it would take more power than your RV can possibly deliver.

My rule of thumb is 40 amps per GPM. A common American shower runs 2 to 2.5 GPM which means 80-100 amps. An ultra-low-flow California shower head is 1.5 GPM which everyone hates, and your heater is barely big enough for that at 60A.

If you could slow flow down to 0.75 GPM, then you could power up one of the two heating elements in the heater (the one with the control electronics on it) and have yourself a usable 30A heater. But it'll be an airplane shower LOL.

Tankless heaters are not continuous loads. That means that if you installed a 50A heater into an RV, hard-plumbed and hard-wired it in, and then ran the hard-wired power out to its very own 50A inlet... yeah, I don't see a problem with that. No sale on the 60A though.

Water flow will not be satisfactory and I would recommend a mega-low-flow showerhead.

Tankless heaters take what the nameplate says.

Tankless heaters take exactly what they say on the nameplate - no more, no less. It's not hard technically to know the power demand of a resistive heater. Your landlord is in dreamland saying it takes 40A. He might mean "it cycles on and off averaging 40A" but that is not the same thing at all. * It might barely work if you can keep hot water flow down enough.

So your concept is possible, but this isn't the right size heater. You could make it a 30A heater simply by disabling (not connecting) one of the two heating elements. (the control electronics piggyback on one heating element or the other; you'd have to find out which by trial and error, or maybe it's numbered #1).

* A lot of people think a 200% load 50% of the time equals a 100% load. For useful work, yes - but for wire heating, no. Wire heating is the square of overload due to the way Ohm's Law works. So 200% overload is 400% wire overheating. Thus, 400% overheat 50% of the time is not what you were hoping for LOL.

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  • My landlord never said that the instruction manual is what says it draws 45 max. U really just confused me. I know nothing about all this.
    – RandaNae
    Commented Feb 11, 2023 at 1:16

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