This paper describes results of recent laboratory tests on a variety of hot water distribution (HWD) system piping configurations and compares HWD piping heat loss to standby losses of several common water heater types. Measured UA factors are given for both ½ in. (1.3 cm) and ¾ in. (1.9 cm) nominal copper piping with various insulation levels. Effective UA factors are also given for a number of common water heater types. This work lets readers evaluate when it makes sense to have more than one water heater in order to lessen HWD system energy losses.