? wiring tankless electric water heaters


Hi, I have some confusion about wiring tankless electric water heaters.
#1 When does one require a sub panel, and if so why?
#2 Is there a distinction made between tankless heaters for space heating and tankless heaters for potable water? There's a tankless company out there with a separate model for each situation. The potable model is not UL listed, should I worry about that?
I have the 2002 NEC. If you could site chapter and verse it would be appreciated.
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how many amps does your perspective heater need? most need a 200 amp main panel just for heating water, so your looking at a major service upgrade probably 200 amp for regular home uses and 200 amps fopr heating water. with new service drop and power company may need to upgrade neighborhood.
how do you heat water currently?
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There is a difference between models for heating water and domestic water, there are also a number of sizes and wattages. You need to determine what you're going to use it for, and how much water you need it to produce, then you need an electric service of adequate size. Some domestic units run at 28KW, or 116 amps @240 volt, which would require your house service to be a minimum of 200 amps

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RBM remove this wrote:

Actually you would need TWO mains one just for heating water!
116 amps or water leaves little to run the entire remainder of home which is today generally 200 amps. you dont want to be at 200 amps all the time.
you will need a pair of 200 amp main services one just for heating water
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Actually, a professional would do a load calculation and determine exactly what size service is needed, but as I stated, and I'm also quoting the manufacturer, 200 amp would be a minimum

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84 amps isnt enough to run a normal home today, and actually you would have what 80% of that?
2 mains will be a minimum
the tankless sellers dont like talking about this...... whats a typical cost a few grand?
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As a licensed electrical contractor, we don't use terms like "normal home" we do load calculations

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RBM (remove this) wrote:

so licensed electrical contractor what kinda home could run on so few amps remaing after the taness is in use?
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moreover the bare minimum today is 100 amp, this home wouldnt have a 100 amps available for all other uses........
no way would this pass inspection
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