What are instantaneous water heaters?

Most instantaneous water heaters are pressure type units with pressure resistant copper or plastic tanks of 1000kPa (10Bar) pressure rating for a centrally installed hot water supply. Such a system can supply multiple outlet points depending on the amount of warm water (l/min), which is determined by the size of the element in kilowatts. These units are compact and have a large element, so water can be heated instantly and continuously.


The outlet temperature is affected by three different factors:

  • Flow rate (l/min.)
  • Cold water inlet temperature (C)
  • Size of element (kW) 

There are two types of units from STIEBEL ELTRON: 


  • Electronically controlled instantaneous water heaters
  • Hydraulically controlled instantaneous water heaters