I just bought a tankless water heater for my house and removed my old tank water heater. I did note that with my new heater, it takes 4 wires my old tank only took one wire.

Would I be able to make a pigtail plug for two of the 4 wires and plug it into the wall or I'm I going to need an electrician?

Look like one set of wires connects to the heating elements and the other to the control panel. Thanks.

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    Please edit your post to include enough detail to answer in any more detail than the comment above. Make and model of the new heater, pictures of your main electrical panel and any sub-panels, possibly the meter as well, square footage of the house for the load calculation, etc. But unless you have vastly oversized, under-used power service, you'll be better off returning the tankless and getting a tanked heater. A service upgrade is expensive, normally.
    – Ecnerwal
    Commented Jun 23, 2023 at 2:46
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    To directly answer your question, "Would I be able to make a pigtail plug for two of the 4 wires and plug it into the wall", yes you would be able to do that. HOWEVER it will NOT work. At best you'll pop circuit breakers, at worst you'll start a fire and burn down your house!
    – FreeMan
    Commented Jun 23, 2023 at 13:38

3 Answers 3


Sounds like you fell for the hype of tankless.

Most of the marketed "benefits" of a tankless heater are misleading at best.

Instant hot water only happens when it's a point of use heater or you are circulating the hot water in the pipes. This is orthogonal to the tankness of the heater.

Less standby losses is barely true, a hot water tank is very well insulated and a cheaper option to reduce standby losses is to add insulation. And if you have a cheaper night-time electricity rates you can use a timer to make it only use electricity at night

Unlimited hot water is true. However when was the last time you needed that much hot water?

The biggest downside of a tankless unit is that instead of a single 20A circuit that a tanked heater can run on, a tankless heater will need multiple 30A or higher circuits to provide full heat depending on the flow rate and the temperature difference you desire.

My suggestion would be to return the tankless unit and instead get a tanked heater with a heatpump. That will be more expensive up front but will save you money in the long run because it needs less electricity to heat the water by the same amount compared to a classic resistive heater.

  • I think less standby losses has to be true since tankless units basically nothing on standby. Whether or not the standby losses of tanked heater make a meaningful difference is another story. Commented Dec 5, 2023 at 15:15
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    @MichaelMior sure, but if you have a cheaper night-time tariff and prevent the bottom heating element from working during the day (and you don't use all the hot water) then even with the losses during the day you will end up cheaper with a tanked heater than with a tankless. Commented Dec 5, 2023 at 15:25

Oh man! so I guess you got an electric tankless WH. They take a LOT OF POWER. I'm thinking you are using the term wire and cable interchangeably. A wire is an individual conductor, a cable can have multiple conductors. As much as I hate to say this, I think you need a pro to sort this out.

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    It can be sensibly sorted out DIY with the box and receipt. Or it can be very expensively sorted out with an electrician and the power company making bank. As for the money "saved" on "no standby losses" you might make that back in 100 years or so. Perhaps 200 depending on the cost of the service upgrade.
    – Ecnerwal
    Commented Jun 23, 2023 at 2:53
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    to pay for the service upgrade. On top of that, some states (looks like WA and OR to start) are requiring the ability to remotely turn off water heaters in high demand times - much as my local utility has done for decades on air conditioners. That is inherently contradictory to tankless, but is not a problem at all (up to a few hours, typically) with tanked water heaters. Commented Jun 23, 2023 at 3:10
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    have to agree with @manassehkatz-Moving2Codidact Electric thankless WHs suck. If the POCO turns off the WH in a tank type, at least you'll have about 50 gallons of HW for a while. With tankless electric, you've got zero HW,. Not only that if going electric tankless DON'T DO IT. They require tons of power and may require a electrical service upgrade: Very likely. Commented Jun 23, 2023 at 3:57
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    @NACCANNate Are you heating your house with the hot water tank water? 100+ dollars a month is a lot of hot water or there is an electrical problem with the tank or a hot water leak. Find the problem or edit your question/make a new question with the information.
    – crip659
    Commented Jun 23, 2023 at 11:20
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    Or, you've also got a lot of other electrical appliances in your house that are contributing to that electric bill.
    – FreeMan
    Commented Jun 23, 2023 at 13:37

To specifically answer the original question (it was indirectly answered already with "don't do this"):

A typical electric tank water heater uses a 30A circuit on a single 10 AWG cable. That has been the standard since the 1950s, and while the heaters have improved some in terms of insulation and, more recently, "smart" controls, the basics haven't changed in decades. (Heat pump water heaters are a different story, but if they are hybrid then they'll use that same 30A circuit and if they are pure heat pump then they may use a smaller circuit.)

A typical whole house electric tankless water heater requires 100A or more, sometimes as high as 160A! Due to practical issues with respect to branch breaker sizing (larger than 60A or 70A often not available or very expensive) and cable/wire issues (larger wires/cables are available but routing those wires from panel to water heater can be very hard to do, plus cables for 40A circuits are much more of a "I've got that on the truck" item than 100A), most residential tankless water heaters are designed to use 2, 3 or even 4 separate 240V circuits instead of 1 really big circuit. That's why this water heater needs 4 cables instead of 1. But even 1 of those is likely to require a larger circuit (40A instead of 30A) than what you already have, so the existing cable is most likely not large enough to safely run the new water heater even at a low usage level.

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