This paper describes results of recent laboratory tests on both "single-pipe" and "bundled-pipe" configurations of high density cross-linked polyethylene (PEX) hot water distribution piping. In both configurations, the pipes were horizontal, uninsulated, in-air. These tests allowed calculation of measured piping heat loss (UA) factors under a variety of different temperature and flow conditions, and additionally allowed measurement of the amount of water wasted to drain while waiting for hot water to arrive. Both the heat loss UA factors and water waste characteristics can be used to compute energy waste associated with the water waste and heat loss. These energy loss effects extend beyond just energy loss from the pipe itself, and include, for example, increases in tank heat loss caused by the need to set temperatures higher to overcome temperature drop of water flowing through the pipe.