Maybe while at home or when traveling, you’ve had this experience: You stand idly by, watching gallons of water go down the drain while waiting for the water to get hot at the shower or sink. Finally, the water begins to warm. Undesirable and annoying, this problem is due to “stranded” water contained in the piping between the heat source and the fixture.
During periods of no demand, this once-hot water gives up heat to the surrounding space and reverts back to ambient temperature. The heat loss rate depends on the type of piping, insulation, air temperature, etc. Longer runs and larger pipe sizes mean longer wait times and more water wasted each time a user needs hot water.