It's no wonder tankless water heaters are becoming a staple of green building. Unlike tank-type water heaters that keep gallons of water at usable temperatures 24/7, tankless heaters provide hot water on demand, saving energy and money. In fact, the Department of Energy estimates that tankless water heaters can be 24 percent to 34 percent more efficient than tank units. According to Jack Banker, manager of tankless sales for Rheem, homeowners can save about 20 percent to 25 percent on their heating bills.
This technology isn't new--it's been in use in Europe, South America, and Asia for decades--but the units have only recently begun to gain traction in the United States as Americans look to cut energy costs. Technology is catching up with demand, too, as vendors are responding with whole-house tankless systems that offer capabilities beyond the capacity of early point-of-use units.
Efficient Options
The basic operation of tankless water heaters is fairly straightforward: When someone opens the hot side of a fixture, water flows into the tankless unit and past a sensor that triggers the heater to bring the water to a pre-set temperature for delivery to the fixture. The quick recovery rates on tankless water heaters allow them to operate on demand, and as long as that fixture is asking for hot water, the tankless unit will continue to heat and deliver it.
Not long ago, availability of tankless units was limited to small-capacity point-of-use systems, which would only provide enough hot water for the location where it was installed, such as a for a bathroom or kitchen sink. Now the majority of manufacturers offer whole-house systems, which can provide enough hot water for large homes with multiple bathrooms. As a result, the tankless water heater industry has grown on average about 25 percent per year since 1999, says Mat Katz, retail marketing manager for Bosch.
Over the years, vendors of tankless water heaters have improved their products' performance by merging gas condensing and tankless technology, adding direct-vent technology, and integrating temperature and carbon dioxide sensors. In addition, the units have gotten more compact and more efficient.
The efficiency of tankless water heaters depends on a variety of factors, including the design and the fuel source. Gas units are about 80 percent to 85 percent efficient because residue heat is lost through the vent pipe, while electric units are nearly 100 percent efficient because they convert almost all the electrical energy they consume into heat. However, some homeowners prefer gas tankless water heaters because they are said to heat water more quickly. (A common complaint of tankless technology is that users must wait a few seconds for the ambient-temperature water to be expelled, the temperature to rise to the set point, and the hot water to flow through the sensor. Some vendors are circumventing this problem by allowing their systems to be installed with a circulating pump.)
