Water heating is typically the second largest energy end use in buildings in the U.S., exceeded only by space conditioning. Better buildings and technologies have reduced many energy loads such as lighting, refrigeration, and air conditioning, but hot water has received much less attention. Recently, however, market forces, accelerated by the ENERGY STAR® Program, have stimulated availability and marketing of advanced water heating products that use much less energy. New work has documented high waste in hot water distribution, and ways to dramatically reduce losses. ACEEE examined sixteen technologies and practices, and found that these technologies can save a cumulative 2.3 quadrillion Btu  through 2025, or about 5% of projected demand in residential and commercial buildings in the year 2025 (43 quads). Collectively, they save an average of 37% of energy over federal minimum efficiency standards  for water heaters and conventional water heating systems. In some cases, the technologies do not promise high returns on investment (fast payback), but the technologies offer new or improved amenity that consumers value (shorter waits for hot water, continuous hot water, etc.). These technologies are likely to be chosen for these tangible benefits, and will also save energy.
Technologies evaluated in this report include: Electric Tankless Water Heaters, ENERGY STAR Heat Pump  Water Heaters, Northern Climate Heat Pump Water Heaters, Add-On Heat Pump Water Heaters, Condensing Tankless Gas Water Heaters, Solar-Assisted Water Heaters, Condensing Gas Hybrid Water Heaters, Non-Condensing Gas Hybrid Water Heaters, ENERGY STAR Non-Condensing Gas Water Heaters, Condensing Gas Storage Water Heaters, Advanced Ground Source Heat Pump Approaches, Drain Water Heat Recovery, Single Family On-Demand Recirculation Pumps, Commercial Point-Of-Use Applications, and Multifamily Building Best Practices.