Tankless Water Heater
Tankless water heater normally use for home that do not have hot water piping ready or no space for tank or want low investment cost.
Tankless water heater is water heater without tank to store the hot water, means the heater must be able to heat the water with higher flow rate than tank water heater. There are mostly two types of this water heater, gas water heater and electric water heater (use heat element).
Tankless gas water heaters must have an energy factor of 82% or higher for Energy Star qualification. Since electricity production itself today has efficiency levels ranging from only 15% to slightly over 55% (combined cycle gas turbine), with around 40% typical for thermal power stations, direct electric water heating is typically the least energy efficient option. However, use of a heat pump can make electric water heaters much more energy efficient and lead to a decrease in carbon dioxide emissions, even more so if a renewable source of electricity is used. The draw back of heat pumps are need very big capacity of heating to make tankless water heater, which practically hard to apply for home usage.
A tankless water heater operating at those same power levels (at 100% efficiency) would be able to supply 1.6 gpm (gallon per minutes) continuously, raising the temperature by 30 °C (54.0 °F). The same unit could supply 1.3 gpm while raising the temperature by 33 °C (59.4 °F). To be able to handle a full house load of multiple uses (at least 5 gpm) with a centralized tankless water heater would require three to four times this power level—somewhat difficult to achieve with natural gas, and very difficult to achieve with electricity. Many tankless water heaters can use over 100,000 BTU/h during high flow, and so require especially large power supplies.
Unfortunately, it takes a great deal of energy to heat water, as one may experience when waiting to boil a gallon of water on a stove (conventional way to heat the water). For this reason, tankless on-demand water heaters need to have a very powerful source to be usable. A standard 15-ampere rated wall electric outlet, by comparison, can only source enough power to warm a disappointingly small amount of water: about 0.17 gpm at 40 °C temperature elevation.