Water heating accounts for a larger share of energy use in residential buildings than in commercial buildings. Shown here are breakdowns of both site energy and primary energy use on a national basis.
Rarely the focus of much attention, water heating accounts for surprisingly large energy loads and environmental impacts. Water heating is typically the second largest energy expenditure in homes (behind space heating) and the fourth largest in commercial buildings (behind lighting, heating, and cooling). In terms of greenhouse gas emissions, a standard residential electric water heater is responsible for nearly half the carbon dioxide emissions of an average passenger car!
This article takes a broad look at water heating. We will examine strategies for reducing hot water demand, measures for boosting overall hot water
efficiencies, and a wide range of options for heating water. Some strategies discussed in the article apply primarily to residential applications and a few only to commercial, but most can be relevant to both residential and commercial buildings.