I am currently considering adding an ELECTRIC TANKLESS WATER HEATER. I have a 200 amp (ITE Load Panel G4040ML1200) with 37 of the 40 poles in use. The tankless water heater requires 4- 30amp breakers. My question is... how can I connect a 125 amp sub-panel to the main panel? Your comments are appreciated. ART H

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Originally Posted by artholl

I am currently considering adding an ELECTRIC TANKLESS WATER HEATER.

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OH god, not another one. I bet the seller conveniently forgot to mention that your 200A service will NOT likely support this monster.


A demand load calculation IS required here. 200 amps will most likely not be enough, and a service upgrade to 320 is very possibly in your future.
When this thing kicks in full blast it will use up half of the whole service capacity.

What else in your home is electric?

Hi Standforty man
I have a oil burner that heats a 1700 sq, ft. condo and feed a hot water tank, plus three room air conditioner, and a washer and dryer, refrigerator, oven, and microwave... in addition to the normal electric circuits. The sellers of the tankless water tanks (Bosch PowerStar AE125 and Seisco RA-28) states that a 200 amp panel is sufficient (? ). I plan to obtain a power load calculation on the main panel.

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Originally Posted by artholl

The sellers of the tankless water tanks (Bosch PowerStar AE125 and Seisco RA-28) states that a 200 amp panel is sufficient (??).

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I wonder, without knowing your home and it's loads, how they can determine this?

200 may be sufficient, barely, but the only way to know is math.