on demand electric water heater

Hello all,
I'm not sure this is the right newsgroup, but I'll give it a shot. I currently have a small electic run of the mill water heater. I'm thinking of replacing it (output is starting to decline) with a electric 'on demand' water heater. Has anyone out there done this, or do you have one? I have questions about where to place it (concerning distance from breaker box), and whether to buy one for each sink, or to buy one for the whole house.
Thanks in advance,
Gary C in EC, NC
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Post in alt.hvac and sci.engr.heat-vent-ac, not here.
Nick
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As I understand it, if you are going to electric you may need to check your available power, as those things take a huge amount of power during the short time they are on and your power supplier may need to do some work on the lines supplying your home first.
I would start with your local electric company. They may be able to help you out on all your questions.
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Joseph Meehan

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I am also thinking about this. I only use hot water a few days a week, so it might be worth the expense. However, I can partially answer your question. You have to find out what size cable you have going to your water heater, and how long it is. I expect it is #10, but you should check to make sure. (Mine was #12 before I replaced it.) Check how many amps the new water heater draws, and go to http://www.electrician.com/vd_calculator.html
Plug the amps, voltage, wire size, and length in, and it will give you voltage drop. If it is under 3% you are okay for voltage drop. The other constraint is that you are normally restricted to 20a for #12 and 30a for #10 for romex, regardless of voltage drop.
I don't know anything about whole house versus point use.
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