Tankless water heaters may not always be the most economical solution. Although tankless water heaters are more energy efficient, the initial investment may not be offset by the savings from operation. This is most prevalent in existing applications.
Tankless water heaters require a significantly higher power supply than conventional heaters. In gas fired applications, the entire gas system may require updating. In electrical applications, it may be necessary to install a high amp electrical service. Either case may substantially increase installation costs.
Most manufacturers require that a water softener be installed where hard water exists. Failure to do so will significantly decrease the life of the heater and may void the manufacturer’s warranty. Should a water softener be necessary, installation costs may increases substantially
Performance is another factor that should be considered. Tankless water heaters perform differently from conventional water heaters.
In a tankless water heater, as hot water is drawn, an inlet valve opens and allows water into the heat exchanger. The heat exchanger is designed much like an automotive radiator with water lines routed through fluted fins. Unlike a radiator designed to cool water, the heat exchanger is surrounded by a high powered heat source. Water, as it travels through the heat exchanger, is heated rapidly providing a semi-endless supply of hot water.
When selecting a tankless water heater, there are two factors that must be considered, the demand for hot water placed thereupon and the lowest ambient water temperature common to the area. Most tankless water heater manufacturers provide a graph that illustrates performance losses based upon these two factors.
Demand is calculated by water supply fixture units (WSFU’s). A fixture’s WSFU is directly proportional to its highest flow rate in gallons per minute (GPM). Therefore, to assure an adequate supply of hot water, the system’s WSFU’s must be figured as though all fixtures were running simultaneously.
Unfortunately, in many applications, multiple heaters may be required to assure ample supply. No matter the heater, performance losses should be expected when pushed to flow rate capacities. These performance losses result in diminished hot water volumes and/or decreased water temperatures. However, these limitations can often be avoided with little effort. Sometimes it simply comes down to changing personal habits; i.e. avoid showering while running the clothes washer.