As houses become better insulated and more efficient furnaces become widespread, water heating energy use can exceed space heating energy use. Although water heater efficiency is improving, the energy impacts of the hot water distribution system delivering the hot water to end uses have been inadequately studied. This paper reports on the initial findings of a field study to evaluate the waste of water and energy in indoor water use in 20 California homes attributable to on-premise hot water distribution systems. The monitoring systems consist of a collection of wireless meters to measure the temperature and flow rates of indoor water use, both hot and cold, at the end use points and at the water heater. The wireless sensor network consists of flow meters connected to wireless motes transmitting data to a central "manager" mote, which sends the information to an embedded computer. The embedded computer is running software to send the collected data through the internet to a server for archiving. The temperature and flow rate data are collected at one second intervals whenever water is flowing.

Data at this level of detail provides the ability to discern how much the hot water remaining in pipes since the previous hot water draw has cooled off before it is used. By examining flow rates and temperatures of the water coming out of showerheads, it is possible to measure amount of water (and energy) wasted while the user waits for hot water to arrive.

Past studies have estimated the waste at showers to be greater than 25%. This paper reports on a project to update those estimates with direct field measurements. Considerations for designing hot water distribution systems for high performance and sustainable buildings will be presented.