Instantaneous Water Heater


 Spirax Sarco is pleased to release the RediHeat instantaneous water heater designed with a unique feed-forward temperature control system to instantly produce hot water within +/-4°F of the set temperature under widely varying demands. This outstanding performance makes the Rediheat the ideal solution for hot water applications where tight temperature control and instant response to changes in demand are required.  The Rediheat features a spiral tubed helical heat exchanger for efficient heat transfer in a compact space. 

The rugged casing and bourdon tube configuration allows the entire assembly to expand and contract without localized stressing, ideal for intermittent cycling common with domestic hot water applications.  The simple mechanical design allows the water temperature to be controlled by a mechanical blending valve that operates based on demand. A manual adjustment compensates for seasonal changes in cold water supply temperature. The unit requires no extraneous power sources, controls or temperature sensors making installation a snap. When maintenance on the helical heat exchanger is required, the coiled tube bundle can be either cleaned in placed or removed for cleaning.  

The RediHeat only consumes energy on demand. This mode of operation can save as much as 40% in energy costs when compared to a hot water tank system.   Vital for domestic hot water applications, the Rediheat has a blending valve fail-safe design. This safety aspect protects consumers from being exposed to hot water at temperatures above set point. Also with the RediHeat’s feed-forward design water is over-heated to 160°F – 200°F in the heat exchanger before being blended with incoming cold water to the desired output temperatures. In this way the presence of stagnant water at bacteria-friendly temperatures is eliminated. 


  • instantly produce hot water within +/-4°F 
  • spiral tubed helical heat exchanger
  • save as much as 40% in energy costs

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