Water heating accounts for 20% or more of an average household’s annual energy expenditures. The yearly operating costs for conventional gas or electric storage tank water heaters in the USA average $200 or $450, respectively.
One way to reduce this expenditure is to use an on-demand, also called Tankless, instant or instantaneous hot water heater. On-demand water heaters are common in Japan and Europe. They began appearing in the United States about 25 years ago.
Unlike “conventional” storage tank water heaters, a feature of Tankless water heaters is that they heat water only as it is used, or on-demand, which means as soon as the tap is opened the heater starts up. To be able to heat the water quickly on-demand, the heat rating of these Tankless heaters is very high.
Once activated, the heater delivers a constant supply of hot water, in most cases, unless too much hot water is demanded in which case the unit may reduce the temperature or flow rate or both… remember, the heater can only deliver a designated amount of energy.
They come in a variety of sizes for different applications, such as a whole-house water heater, a hot water source for a remote bathroom or hot tub, or as a boiler to provide hot water for a home heating system.
They can also be used as a booster for dishwashers, washing machines, and a solar or wood-fired domestic hot water system. You may install an on-demand water heater centrally or at the point of use, depending on the amount of hot water required. For example, you can use a small electric unit as a booster for a remote bathroom or laundry.
Using low-flow shower heads and water-conserving faucets is a good idea with on-demand water heaters. On-demand water heaters cost more than conventional storage tank-type units.
The appeal of on-demand water heaters is not only the elimination of the tank standby losses and the resulting lower operating costs, but also the fact that the heater delivers hot water continuously.
Most tankless models have a life expectancy of more than 20 years. Storage tank water heaters last only 10 to 15 years. Most tankless models have easily replaceable parts that can extend their life by many years.