Instantaneous/Tankless Water Heaters

Instantaneous or tank-less water heaters are very common in Europe and Asia. Unlike storage heaters, instantaneous water heaters heat water only upon activation by switch or water flow.  Basically, an instant heater switches on when water enters the heater inlet.  Then, the heating element or gas burner activates, heating the water that then goes towards the outlet.

Instantaneous heaters are commonly categorized as either single point or multipoint heaters.  These are applications of the heater.  With single point application, there is only one point of use of hot water -- usually the shower -- and the water isolation point, where the water flow is controlled , is located before the inlet of the water heater.  With a multipoint application, hot water is supplied to two or more devices, like the sink and the shower.  Each device supplied by the multipoint application is an isolation point.  Because the isolation points are located after the outlet of the multipoint heater, the water through the heater is pressurized.

Advantages:

  • They do not suffer from standby heat loss
  • They have much smaller space requirements

Disadvantages:

  • They usually will have a certain minimum flow rate required to activate
  • Water temperature is dependent on volume of water; for a given heating setting, higher/stronger water means lower temperature
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