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Water Heaters

Domestic Hot Water (DHW) use accounts for about 12% of total household energy use in the United States, making it the third largest energy-use category, after heating and cooling. There are a wide variety of water heating technology options available to homeowners, but gas and electric tank-type water heaters are the most common. In addition to the common gas and electric water heaters, there are also tankless, or instant, water heaters in both gas and electric. A new type of electric water heater, the heat pump water heater, has the potential to cut electrical energy use in half relative to standard resistive electric water heaters. Recent innovations in gas water heater technology, such as condensing gas water heaters, can cut the demand for natural gas in regions where gas water heating dominates. Solar water heating is another water heating option that can drastically reduce DHW energy use.

Gas Water Heaters

Gas water heaters make up the majority of water heaters in homes in the United States and are generally more efficient in terms of source energy consumption and operating cost. There are number of different types of gas water heaters, all with different functionality and intended uses.

Electric Water Heaters

Traditionally, the only type of electric water heater has been an electric resistance water heater, which is inefficient but inexpensive. Within the last several years, tankless water heaters and heat pump water heaters have joined electric resistance water heaters in the electric water heater class. Tankless water heaters still use electric resistance to heat water, but only when water is needed, eliminating the energy losses due to tank losses. A heat pump water heater primarily uses a heat pump to improve the efficiency of the water heating process, but also has electric resistance backup heaters for high demand situations. Both types of technology can be an improvement over standard electric resistance water heaters, if applied appropriately.


Desuperheaters are paired with a of refrigerant-based appliance - either an air conditioner or heat pump - and uses a heat exchanger to pull heat from the refrigerant after it passes through the compressor but before it goes to the condenser. This excess heat is used to heat water for domestic use or supplement the water heating from a traditional water heater.

Solar Water Heaters

Solar water heaters collect heat from the sun to heat water for domestic water use. There are a wide range of different types of residential solar water heaters, ranging from simple to very complex. Usually, a solar water heater consists of a collector that sits on the roof or on the ground near the house and a tank for holding the newly hot water. In most climates, backup heating is required to supplement the solar water heating in the event of cloudy days. Backup heating can be provided directly in the storage tank (either electric resistance elements or a gas burner) or could be found in a separate water heater. In warm climates, water is warmed in the solar collectors and fed back into the home's domestic hot water system. In colder climates where freezing is likely, a fluid such as glycol is heated in the collector instead and passes through a heat exchanger to transfer the heat to the domestic water system. This arrangement prevents freezing and increases the longevity of the system.