On Sat, 15 May 2010 16:57:59 -0500, "
wrote:

If the pipes are insulated, they don't lose that much in one run. Heating water
with gas here cost about half what letting the dishwasher heat it electrically
costs.

Few pipes are insulated, and even fewer in walls. All pipes, no matter how
much insulation, will lose the heat in the entire run each cycle.

I have a PEX manifold system. When hot is demanded, the cold is sent
back to the water heater. I get hot water faster that way. Granted all
systems are insulated....