> I think the idea of tank water heaters is somewhat flawed. Why use
 > the energy to hold a lot of water at that temperature when you can
 > just heat what you need when you need it with a demand heater? OTOH,
Ian,
 The idea of a tank-type water heater is pretty simple: it requires a LOT of 
ommph to heat water as fast as most folks want to use it. Do the calculations 
sometime and you'll see what I mean. A tank can be heated by a relatively 
small source over a longer period of time, then used at a fairly rapid rate.
 
The only reason for any energy consumption to "hold a lot of water at that 
temperature" is because of thermal loss. This is really pretty darn minimal 
in today's water heaters. I think most folks would be amazed at how little 
energy it takes to keep water hot.
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