Types of Water Heaters

Water heaters come in a variety of types. Some are defined by the type of energy they use. Others can be defined by the way they heat or store hot water. The main categories of water heaters are the traditional tank heater, the heat pump water heater, the solar water heater and the tankless or on demand water heater.

Tank water heaters use natural gas to heat an element, then transfers that heat to the water by means of simple conduction. Tank heaters have to run continuously to hold water at a high temperature while it waits to be used. This makes tank hot water heaters fairly inefficient when compared to newer styles of hot water heaters, but the tank heater's relatively low start-up cost still makes it a popular model in homes today.

Heat pump water heaters were an early attempt at introducing energy efficiency to tank water heaters. Just as heat pumps heat and cool houses by moving heat from the air or ground, heat pump water heaters remove heat from air and geothermal heat sources and pump it into the water heater tank. While this is an improvement over the traditional tank water heater, it still does not provide a large amount of energy savings and is costly to repair and replace.

Solar water heaters use collectors to gather solar heat and transfer it to water. These systems are typically built on rooftops. Solar water heaters use a heat collector to transfer solar heat energy to water. The collector system can be as simple as a glass topped insulated box with a black painted metal collector over copper tubing, although more complex systems are available. Solar systems in cool climates usually have electrical or gas heating as backup for cool winter months. While solar systems are extremely efficient, initial setup and maintenance costs tend to override any energy savings.

Tankless or on demand water heaters use a system which only heats when the water is needed. When the hot tap is turned on, cold water flows into a pipe within the water heater. The system heats the water as it flows through the pipe. This makes the tankless water heater one of the most efficient water heater's currently on the market. Large consumers of hot water have a choice between installing a whole house unit or separate small units near bathrooms, kitchens and high-flow appliances. The warranty on tankless systems is usually more than twice as long as the warranty on traditional tank units. This means that tankless systems beat tank hot water heaters in efficiency, price and maintenance costs.

Most kinds of hot water heaters still appear in the modern home. Heat pump systems boast a mild efficiency improvement over traditional tank systems, although traditional tank systems still fit the low start-up cost niche. Solar systems are among the most efficient, but the energy savings goes not yet offset the high startup cost. Tankless water heaters improved efficiency and lower maintenance and replacement costs currently place them in the lead over other models.