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I'm looking into researching about installing a Hot Water Tankless system.

Specifically I want to install the following:

Rheem Tankless Water Heater 2.14 GPM 13 kW Self-Modulating Electric Wall Mount

It has the following power requirements: (RTE 13)

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I had a few questions:

Lets start with the obvious, I'm not 100% my service is adequate. I have 100Amp service in a 1 Bedroom trailer that utilizes Electric Heat. I have 2 20Amp breakers dedicated to two different Electric Baseboards as well as the usual appliances. As it is a one bedroom it isn't often that many appliances are being used simulataniously, but I do want to be not tripping anything just by using hot water + heating the home.

  • Can my setup handle this hot water tank?

Here is an image of my breaker and the panel breakdown:

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If so, perhaps this should be a seperate thread, but I'm just putting it all ine one for now....

  • Can I upgrade the current wire to AWG 6 and the breaker to 60Amp and hook that up to my current hot water tank system. The reason being I'd like to get the wiring/breaker setup so that when I go to install the tankless system it's "plug and play". I'm not sure if the different thickness of wire and size of breaker will matter if I am using a higher rated wire/breaker than needed. I'm guessing people just don't go higher because it costs more, but I'm not sure.
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  • How many watts do the current stove and the current baseboard heaters pull, as well as the bathroom heater?
    – ThreePhaseEel
    Oct 21, 2019 at 11:44
  • I'll have to test with a clamp on meter, but in starting to change my mind slightly, not sure if the above tank would work to fill my bathtub or not, so many uncertainty like will the GPM be sufficient etc. I'm hoping to move in the next few years and might look towards getting this in my next place. Possibly a propane version depending on next homes heating setup.
    – FreeSoftwareServers
    Oct 21, 2019 at 11:47

2 Answers 2

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Can you install 6 AWG Cu wire?

Or 4 AWG Al wire? You bet, that'll be fine. Upgrade away. You are always allowed to oversize wire.

Further, at these large sizes, the new aluminum AA-8000 alloy is perfectly accepted. It's legal all the way down to 15A circuits, but home inspectors will start writing nasty-grams in your buyer's report if they see it below about #4 size.

Can you upsize the breaker on the existing appliance?

No No No No No.

Breakers don't just protect wires. They also protect appliances.

You need to follow the appliance's instructions and labeling and fit the breaker they tell you to. Or find its actual watts/VA/amps, convert to amps, derate by 125% and use the next breaker size up, and wire appropriate for that breaker. 4 AWG Al is appropriate for a 20A or 30A breaker (way too big, but as said, bigger is fine.)

Is your panel ready for this heater?

Do you have the physical breaker space? Yes, because you'll pull the existing water heater breaker.

Does your panel have the capacity? That is a sobering question given your panel's present loads. I don't have the expertise to answer that.

AFCI outlet

A GFCI outlet is alright. An AFCI outlet is worthless. AFCIs protect the wiring in the walls not appliances (except they are rather useful for electric blankets).

There are only two places AFCI protection makes sense: at the breaker itself (and QO certainly makes that). Or just past the breaker at a receptacle or deadfront, which may be cheaper by enough to justify a short stick of EMT conduit to a metal junction box.

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  • The stuff about AFCI I'm not sure why you added that, I have no AFCI breakers but I do buy combination GFCI/AFCI outlets when I need just GFCI. (I had to remove that one at my washer though as it kept tripping). It's great to know I can upgrade the wire, I realize nobody is going to say I can upgrade the breaker, I was thinking just short term and more "would it work", but I realize it would not perform it's function of protecting the line. I'm going to get a clamp meter and do some load tests, but I'm leaning towards the smaller RTEX-11Kw
    – FreeSoftwareServers
    Oct 21, 2019 at 22:16
  • Concerned about filling my tub though and might just have to give up completely. Posted a separate thread for that concern here --> diy.stackexchange.com/questions/176871/…
    – FreeSoftwareServers
    Oct 21, 2019 at 22:18
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Being a small home and only seeing 2 circuits (240v baseboard 20 amp heaters) you would be pushing the service, but it might work, you would be removing the double pole 20 in 1-3 and installing the 60 amp or going from 5kw to the new 13kw or April 8 kw higher draw or approx +33 amps while in use compared to the old one. We don’t actually add the breakers to figure out the total load on the service, where I could see a problem in the winter when you need full power on the water heater with the 2 base board circuits running the actual draw there could be right around 80 amps having the dryer or oven going along with some lights and you may trip the main. So it is very close. I would want to monitor the power usage with the above turned on and see what the actual draw is before saying yes or no.

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  • Yeah, the place is basically a bachelor pad so only 1 person or couple. I would sacrifice not using dryer + hot water or whatever combination it couldn't handle to have unlimited hot water + energy savings. I'm debating on the RTE 9 now though, which might be a better fit for my place. I'd be able to use everything without tripping I think, but would not have as much GPM, but as it stands I don't start a shower anyway with the laundry going!
    – FreeSoftwareServers
    Oct 21, 2019 at 5:28
  • I'm still confused about one question, can I upgrade the breaker/wire gauge and still use the old hot water tank so that I can "compartmentalize" the installation process.
    – FreeSoftwareServers
    Oct 21, 2019 at 5:29
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    You can upgrade the wire now and buy the breaker but you need to stay with the current breaker because a 60a breaker is two large for your current water heater. You will probably have to pig tail from the large wire to smaller as the larger wire won’t fit your existing breaker.
    – Ed Beal
    Oct 21, 2019 at 12:21

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