I'm installing a instant on demand water heater that requires a 220v - 40 amp circuit and would like to know what size wire is required for a 50 foot run. ??????

  • This water heater can be run on 4 different settings. 10, 20, 30 or 40 amp circuit. I'm looking to use the 40 for maximum efficiency – Clete Wyland Jul 13 '19 at 21:45
  • Hello, and welcome to Home Improvement. It's best if you edit new information into the question text, rather than posting it as a comment. And, you should probably take our tour so you'll know how best to participate here. – Daniel Griscom Jul 13 '19 at 21:49
  • Are you planning to run a cable (NM or armored/metal-clad), or individual wires in a conduit? How is the rest of your house wired, for that matter? – ThreePhaseEel Jul 13 '19 at 22:05

8 AWG copper wire or 6 AWG aluminum. For the ground wire, 10 AWG copper.

Most on-demand heaters need 2 wires + ground, but check your installation instructions to be sure it doesn't need 3.

Keep in mind a 40A on-demand is a pretty small heater and you may need to reduce flow to get hot enough water.

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