If not, don't even consider it. The electric ones suck so much juice that most houses can't use them without very expensive upgrades to the electrical system.
I got into something of an argument with somebody over at slashdot about this. I've actually used one; Well, more of a 'microtank' over in Germany. 240V, 30A. You could barely get a useful shower out of the thing.
many of the electric heaters will use 2 or 3 double pole 40 to 60 amp breakers each. check the amount of space in your main box to see if there is space.
Sounds odd - all the ones I've seen use a single breaker, 120V for the small ones, 240V(double pole) for the bigger ones. Seen them as high as 100A, which is almost double my entire service. A 'modern' 200A can service it, not much else. EDIT: I think I know the reason for multiple breakers - they're using multiple heaters; perhaps in-line to get the necessary boost.
Thoughts about on demand/tankless heaters;
1. More relevant with electrics: They can't be tied to a 'off peak' system - tends to wipe out any savings you might have.
2. Both electrics and gas units are normally LESS efficient than high efficiency tank units. Note: I'm not talking about standby or average use loses, I'm talking about their efficiency at heating water in the first place. A tanked NG unit will often be over 90%, a tankless only 80%. Only your exact usage patterns can determine how much getting rid of the tank will actually save you. NG tankless tends to compete more favorably due to the increased losses due to the flue in gas units. Electrics tend to be better sealed, reducing standby losses.
3. For electric, if you
really want to save energy, go with a heat pump system. They make air source to water heater ones. Dehumidify and cool your basement even as you heat your water - Turn a 240V@30A draw into a 240V@5A one.
ask him how he plans to retrofit a recirculating pump to a tankless.... i see some problems there
Probably simple enough, just start pumping water when it gets cold enough, firing up the heater until the hot reaches the sensor. Problem: You're simply turning your piping into a rather poorly insulated tank. My 55 gallon electric with 3" of solid foam insulation isn't cooling down anytime soon, even without power. My electric bills dropped 20% when I installed it over the cheap 50 gallon previously there.
the amount of energy savings is often much overstated, and as someone else mentioned if they are sized improperly they can be a real problem.
I agree on the savings; some families have reported INCREASED energy bills after installing one. I'd need a 100A one to serve my house, seeing as how I'd need at least a 50F increase, due to my nice, cold, incoming water.
your best bet is to put the heater near the point of most use such as a shower, and insulate it well. you can also put timers on them to shut off the heat when you are not home, just like you do with your furnace. much cheaper than a tank less that way.
Why would you put a timer on it? The whole point of a tankless is that it doesn't turn on unless there's water flow, right? By the same token, insulating it is likely to do little.
