I'm installing a new instant water heater. The unit requires a 6 gauge wire when there was only a 14/2 (undersized?) wire going to the previous boiler-style hot-water heater. The electric panel is in the garage roughly 40ft away straight shot through the attic.

Now I don't fuss around with the breaker panel (I'll hire an electrician for that). I mainly have two concerns. Can 6/2 wire like this be run in the wall, namely the stretch from the attic down to the heater which is in a closet and down to the breaker from the attic.

And also, do I need a subpanel? Or can the 60amp breaker be installed in the master panel and the 6 gauge wires be connected in some kind of enclosure using a 6 gauge terminal block to the conductors of the water heater?

  • You call this an "instant" water heater, but I can only assume that it is a tankless water heater. Is that correct or is this an electric tank heater? If this is a tankless, will it be installed next to the point of use? If not and if this is a central electric tankless water heater, then "instant" it will not be. It will supply "endless" heated water, but the heated water will not come any faster than a tank, and the water will be nowhere near as hot as that supplied by an electric tank or a gas fired tank water heater. How many and what points of use will this heater supply water for? Mar 9, 2018 at 10:09
  • I guess I got my terminology mixed up: it is a tankless hot water heater close to point of use. It will supply two bathrooms hot water about 5ft and 10ft from its location respectively. It is rated for "small apartment" usage, but here in florida it can output around 3gpm so it should be fine. Indeed I know that typically it takes a 10-20 seconds for it to start generating hot water despite it saying "instant".
    – Alex
    Mar 9, 2018 at 20:07

1 Answer 1


You can use that 6/2 WITH Ground wire and run it down through the stud just like 14/2.

I am surprised that it requires 6 gauge wire - What voltage and how many amps ? I know you mentioned a 60 AMP breaker but that does not tell unit amperage as there are codes and guidelines for proper CB ratings.

That has to be one serious Hot Water Heater - I would have expected #8 or #10.

As for your mention of 14/2 to the boiler unit:

  • Any chance your old unit was a gas unit ?

That would explain the 14/2 wiring 120VAC for control circuits and gas to do the heavy lifting.
Just an FYI they do make Gas Powered Instant Water Heaters as well.

A 60 AMP breaker might be fine in the same panel as long as your panel will support the additional load. Since you are calling an electrician get quotes an electrician will tell you if your panel will support the added load or if you need a sub panel. This is all dependent on what you already have - a panel model number with pictures of behind the face plate cover would be helpful.

Since your Instant Water Heater is 220V you will not need an AFCI breaker, I would recommend a GFCI breaker.

  • 2
    Tankless point of use electric heaters do use a lot of power. Whole home electric water heaters can use 120A at 220v! OP probably had a small (1-2 gallon) point of use tank there previously since it was only 15A.
    – JPhi1618
    Mar 9, 2018 at 15:19
  • I agree jphi1618, I have upgraded home services so they could have tankless electric, with several of these we had to add point of use smaller units to bring the water to a warm enough temp, in one case after upgrading the owner was so unhappy we converted back to a large tank heater.
    – Ed Beal
    Mar 9, 2018 at 18:40
  • Original one was electric as well. According to the spec sheet the unit requires a 60amp breaker and draws a max of 54amps (the wire specs also came with the unit). cdn.globalimageserver.com/…. Tbh I think I am just going to run the wire and have the electrician do the rest. If it were 14/2 or regular wiring I'd be comfortable doing it.
    – Alex
    Mar 9, 2018 at 20:03
  • 1
    Before buying wire and installing it you should check with the electrical inspector for your jurisdiction. He/she will tell you what wire gauge is legal there for a 60 A breaker. Also, since this is a much higher power demand than the current heater you must find out if your panel can supply it. Is there a separate water heater for the kitchen and clothes washer? What type? Mar 9, 2018 at 20:39
  • The specs say that the Eco 11 operates two 5.5 kW heating elements at 220 V (so 11 kW). I would think that you have 240 V so just to understand what you are getting into you might want to find out from the mfgr how the Eco 11 would operate at 240 V. The current draw might be less or the same or higher depending on how the unit works. Mar 9, 2018 at 20:59

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