I want to replace my electric water heater with a gas tankless water heater. My current water heater like most electric hot water heaters takes 220 and the tankless gas water heater uses 120. The room I am installing in has no outlets. Can I use that 220 line and get a couple out 120 15 or 20a outlets out of it. Maybe with a sub panel type set up or if I can't do that if I can at least wire the new 120 water heater without running a new line. Thanks in advance.

  • How many wires are in the cable to this water heater and what color are they? Apr 28, 2018 at 23:37
  • It is 10/2 ROMEX. The color I am not 100% sure as I have not in hooked it from the water heater yet. I assume it black white and bare. Apr 29, 2018 at 12:57
  • 10/2 + gnd? So you will get one 120-V 20-A circuit out of it which will certainly do for the tankless gas water heater which will draw practically nothing since the power is just for the controls. I presume this room has no gas supply currently so you will have to bring in a 3/4" or 1" gas line for the new gas water heater and you will have to have a flue installed. All this on top of the purchase price of the water heater will be $$$$. Is the current electric tank WH inadequate? What size room is this? Is a furnace also in this room? Apr 29, 2018 at 20:13
  • Do you know if your house has a large enough gas line to supply a tankless gas water heater? Where will you get combustion air? A new house under construction in our neighborhood is being fitted with two 180,000 BTU/h tankless heaters which each exhaust through the roof through a coaxial intake air/vent to also bring in combustion air. The house has a 1.5" main gas line (meter to house to attic) which then divides into smaller diameter for various gas appliances. Apr 29, 2018 at 20:21
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    I plan on running Concentric vent horizontal and exit out the side of my house. There are no windows on that side so no worries there. Apr 30, 2018 at 13:57

2 Answers 2


In the panel, move the white wire to the neutral bar, and move the black to a 20A breaker. Fit a 15A or 20A duplex receptacle. And you're done.

You can use up to about 19.5 amps of power off that receptacle, since the water heater won't take much.

If you want two full circuits good for a total of 30A@120V, in the main panel, leave the black wire on the 30A breaker, still move white to neutral. Then fit a subpanel, of any size. Black to a hot pole, white to the neutral bar, ground to a different ground bar that is isolated from neutral. Only every other row of breaker spaces will work. Fit two 15A or 20A breakers and use each one for a different circuit. If you place the breakers in the wrong row, don't bust out more knockouts, switch the black wire to the other hot lug.

  • Are both of these options within code? I like the second option better but don't want to create a mess if I go to sell the house. Apr 29, 2018 at 13:02
  • Absolutely it is. They don't really make 120V panels, don't need to. Your other option is split the black wire with a wirenut and two pigtails (same size wire) and feed both hot lugs, but that is uglier because it has the illusion of 240V power but is not. Apr 29, 2018 at 13:17
  • If there is not a 4 wire feed to the waterheater this will not be legal, straight 240v water heaters do not require a 4 wire but a sub panel would, running a 120v panel would be a waste in my opinion with 10 awg wire.
    – Ed Beal
    Apr 29, 2018 at 20:04
  • @EdBeal explain why does a 120V subpanel need a 240V feed? We are retasking the white wire to be actual neutral. There is no second hot. Apr 29, 2018 at 20:14
  • I think it would be a waste to install a single pole sub the panel , breaker & outlets required are close to 10× just replacing with a duplex 120 in my experiance most water heaters are close to the main if a sub is needed and it is not it is a waste of $ in my opinion to install a hack like this. Just my opinion but the jobs I have replaced like this were usually DIY with no thought and the new owners thought they had a real sub not a hack job,,, I have seen this 2 or 3 times over my years and they were all upgraded properly.
    – Ed Beal
    Apr 30, 2018 at 16:56

I would swap out the 240v double pole breaker for a 120v single pole and change the outlet. It is ok to use larger wire as most water heaters are wired with3 wire 10 awg this is small for a sub and the sub would need 4 wire. If wired 4 wire #8 I would put in a small sub, but if 10awg just convert it to 120v you need.


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