I am looking to add a tankless ecosmart 27 water heater to my barn. I'm currently running a 60 gallon electric water heater supplied by a 240 line. However, the tankless system requires 3 supply lines. Is there any way use the current 3wire 240 supply line to supply the sub panel?

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  • What do you mean 3 supply lines; water lines or electric lines? Please explain in more detail.
    – d.george
    Commented Jul 12, 2017 at 9:47
  • I think that OP is asking if there is a way of running a 3-phase heater on their single-phase supply.
    – Niall
    Commented Jul 12, 2017 at 10:22
  • 1
    @Niall don't confuse "split phase" and "single phase"
    – Tyson
    Commented Jul 12, 2017 at 11:32
  • 4
    Nope, it requires 3 1ph 240V 40A circuits -- it's a subdivided single phase load. Commented Jul 12, 2017 at 11:49
  • 1
    Presumably the ecosmart 27 has three separate heating elements, each 9 kW giving 27 kW total. Each element would be powered by a separate 240 V circuit with a separate 40 A breaker. So the ecosmart 27 would require three separate cables each Cu 8-2 + gnd or Al 6-2 + gnd and three 40 A breakers. youtube.com/watch?v=9lQw8Po2H04 Commented Jul 12, 2017 at 15:20

2 Answers 2


The existing single cable cannot be used by itself to power the ecosmart 27. You need three separate cables each from its own 40 A breaker. Each cable must be Cu 8-2 + gnd or larger (presumably Al 6-2 + gnd would work if the terminals in the ecosmart are approved for aluminum conductor).

See https://www.youtube.com/watch?v=9lQw8Po2H04


No, you cannot use the existing line to supply the new tankless heater. The existing cable contains 10 AWG conductors, which are only good for supplying 30 ampere loads. The ecosmart 27 requires three 40 ampere 240 volt circuits, which requires at least 8 AWG copper conductors.

The nameplate on the unit says that it draws a maximum load of 112.5 amperes. If you wanted to supply the unit from a second panel, you'd need to feed that panel with at least 2 AWG copper conductors (or 1/0 aluminum). Feeding the heater from a second panel would be done as follows:

  • Install a 125 ampere double pole breaker in the main panel
  • Run two 2 AWG copper conductors (and a properly sized ground) between the two panels.
  • Install the three 40 ampere double pole breakers for the heater in the second panel.
  • Run six 8 AWG copper (6 AWG aluminum) conductors (plus properly sized grounding conductor(s)) from the second panel to the heater.

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