Tankless Hot water heater 220v/100amp

[Anonymous]

Hi, I intend to buy a tankless water heater that requires 220v / 100amp. So, I asked my maintenance guy to do a bid on converting from 220v / 40amp to 220v / 100amp. He said that all that was required was to replace the breaker with a 220v / 100amp and replace the wire with a larger gauge.
My question is, does that sound correct? He will be changing nothing that goes to the breaker box. He will only change the breaker and wire gauge. This seems to say that the amps are already in the box and ready to be used and it only takes materials that will allow that much juice to flow through them.
It is very important to me that the wiring is safe and efficent. So, I wanted a second openion before I pay for something that is not sufficent.
Thank you for your time.
Dood

[imported_joed]

Without knowing what else is in your panel and its size your maintenance guy is correct.

[Dood]

Thank you, I just wanted to hear it from another person too.
Dood

[Wgoodrich]

When you add that much dead load onto an existing service you should perform a demand load calculation to see if the service is large enough amp rated to carry that added load. You can perform you own demand load calculation by going ot the following link. The answer to that demand load calculation would be hte mininum service size allowed by the NEC to serve you home with the added load included as a fastened in place appliance.

http://www.homewiringandmore.com/homewiringusa/2002/definitions/demandcalc02/DwlingDmdCalc02.html

HOpe this helps

Wg

[Dood]

T hank you very much. I have been reading some of your posts and you are very knowledgeable.
Have a great day.
Dood