legg  wrote:   
   > The common solution with 'flash heaters' is to turn the system   
   > on x minutes prior to use and turn it off when the demand ceases.   
      
   Energy payback: W1*(t-tcool)+Wh =W2*t   
      
   Where:   
   W1 is the average wattage at lower T   
   W2 is the average wattage at 98°   
   t is the number of hours   
   tcool is the time to cool down from 98° to T   
   Wh is the energy required to re-heat from T to 98°   
      
   W1, W2 are known from my previous   
   tcool is unknown and I tried to guesstimate it   
   Wh is calculated as:   
      
   T° C to 98° C	Wh	Wh *1.25   
   90	37.24	46.55   
   80	83.8	104.75   
   60	176.91	221.14   
   After 6 hrs 21°	358.48	448.1   
      
   Second column from an online calculator. Wolfram Alpha as example. Third   
   accounts for the not perfect energy transfer.   
      
   Solving for t is simple. Then the fun begins.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)