I currently have a 50 gallon water tank in my house and I want to replace it with a tankless system. The primary reason to replace it is space.

I recently installed 2 HeatWorks Model 1 units to test them out (I left the tank in, luckily), but that failed miserably for reasons not germane to this question. I'm returning those and now I'm left with 3 separate 30A electrical lines, including the one the tank is currently using.

I would like the heater to be able to produce enough hot water for 2 simultaneous showers. I've seen that the units that can handle that tend to demand 60-70Amps. It's not easy to run new electrical to the place where the water is, so my question is whether a unit exists that takes multiple electrical lines. This would allow me to use the 2 or all 3 30A lines.

2 Answers 2


Yes, most larger "whole-house" units require two or even three circuits. Problem is most of those require two or three 40, 50 or even 60 amp circuits.

You will have to do some research to find one that will supply your needs but only requires three 30A circuits. I will say, don't get your hopes up.

  • Europe is a big reason so many hot water heaters are 3-circuit. There, 3-phase 230/240V "wye" goes to every poletop. Normally they only bring 1 or 2 phases into the home, but it's no big deal to ask for all 3, for instance to run a demand water heater. So there's hope to find a 3x30A one. Commented May 21, 2016 at 3:46
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    I don't doubt that a 3x30A unit exists, I just wonder if it will be large enough for whole -house. Commented May 21, 2016 at 14:18
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    I don't think the OP knows what he needs. He says 60-70A, yet is looking for something that will require 90A worth of circuits. A unit that draws 60-70A will NOT provide enough for a whole house. Not even close. I have done under sink units that had a 60A circuit, not even enough for a single shower. Commented May 22, 2016 at 1:28
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    He has evidently done some homework, but may be relying on manufacturer claims such as those I've seen that such a unit can run two 1.5gpm showers in warm-weather states like Florida. That's really something he has to engineer for himself, depending on his tolerance, showerhead flow, incoming water temp, too many variables. He's clearly willing to experiment and innovate, and that's what it would take. I would use low-flow heads and also add cheap shower water filters, they are annoyingly effective at constricting flow. Commented May 22, 2016 at 1:59
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    Thanks for the comments guys. It's true, I was underestimating the amperage needed by a large margin. I was just looking at commercially available options and all of the 4+ GPM units require 3x 40A at least. I might just have to keep my tank in place and suck it up. Too much trouble :(
    – 0x6A75616E
    Commented May 23, 2016 at 0:15

I just installed a tankless water heater - Installed Electric Tankless Water Heater - Internet loss when active

27kw is about the minimum you want for a whole house (unless you live in a very hot climate), as others have pointed out this will be 3x40amp 8awg lines.

I'd recommend installing something similar and pulling new cables if you are serious about tankless.

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