Residential water heaters are used to provide hot water for showering, dishwashing, clothes washing, and other household needs. Residential water heaters use diverse energy sources including electricity, natural gas, propane or fuel oil. There are two main types of residential water heater technology: storage and instantaneous water heaters.
DOE finalized the current standards for residential water heaters in April 2010, and they took effect in April 2015. The efficiency requirements vary depending on the type of water heater and the rated storage volume. For storage water heaters with a volume greater than 55 gallons, the standards require a heat pump efficiency level for electric products and condensing efficiency level for gas products.
EPA plans to issue ENERGY STAR specification version 3.1 for residential water heaters by mid-2017. The purpose of the revision is to convert the current ENERGY STAR specification from the energy factor (EF) metric to the new uniform energy factor (UEF) metric while keeping efficiency levels constant.
Residential water heating represents 18% percent of total annual household energy consumption in the U.S. About 48% of households have natural gas water heaters, while 45% have electric and slightly more than 6% burn propane or oil.
All storage water heaters waste energy keeping water hot even when no hot water is being used. Thicker tank insulation can decrease standby losses for all types of storage water heaters, but the cost-effectiveness of more insulation can be low for already well-insulated tanks. Electric heat pump storage water heaters have demonstrated 50% savings in energy use compared to electric storage water heaters and condensing gas water heaters can reduce energy consumption by about 25% compared to conventional gas storage units.