Thanks to all who replied. I used 3/8" pipe home runs to all sink &
lavatory hot water valves. Water flow decrease was measurable, too small
to notice in normal use. Wait time for hot wated decreased sharply due to
shorter runs and the fact that a length of 3/8" pipe holds only 56% as much
water as the same length of 1/2" pipe.

I don't know if code approves of the 3/8" pipe, but I love it!

On Thu, 03 Apr 2008 07:35:34 -0400, wrote:

I need to run hot water pipes to the various appliances in my home. Some
of the appliances (lavatories, and sinks) will use relatively small amounts
of water at a time but will be used frequently, while others (tubs &
showers) will be used less frequently but will use much more hot water at a
time.

I would like to minimize wasted energy and the time spent waiting for hot
water at sinks and lavatories while still providing sufficient flow. At
tubs & showers, having a good flow rate is more important and the wasted
energy & wait times do not matter so much because of the less frequent use
and large amount of water per use.

Running different size how water lines to the same room is no problem at
all. I realize that, occasionally this will result in having to fill two
pipes but in our situation this will seldom happen. A recirculating system
is not ennergy efficient so I don't want to go that way.

Given the above, what size pipes should I run to:
Sinks & Lavatories:
Tubs/Showers:
Dish washer:
Washing machine:
(Whirlpool tub: 3/4" since valve inlets are 3/4")

Many thanks for any help!