Why do schematics always show backup water heater in line?

Discussion in 'Solar and Geothermal Water Heating Forum' started by kjkrum, May 9, 2012.

  1. kjkrum

    kjkrum New Member

    Messages:
    5
    Location:
    Tucson, AZ
    In reference to schematics like the first one on this page: http://homepower.com/basics/hotwater/

    Why do schematics like this always show the backup heater in line with the output of the solar heater? Wouldn't you then always be using your electrically-heated water first? It makes more sense to me to install an electric heater in parallel with the solar heater, with isolation valves so you could run the backup heater only when needed.

    If it makes a difference, I live in Tucson, AZ. I know people around here with solar HW systems with no backup heater at all.
  2. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,783
    Location:
    Long Island, NY
    To keep the water pipes from freezing in areas that need such protection? Or/also to provide enough heat when its dark out and you need hot water when your storage tank is not hot enough?
  3. Terry

    Terry Administrator Staff Member

    Messages:
    14,749
    Location:
    Bothell, Washington
    The diagrams look right to me.
    The last thing in the line should be a conventional water heater. What happens at night if you don't have a heater?
    The Solar goes before the heater, and the heater is only needed if the solar hasn't done it's job.
    I like the tempering valve to prevent scalding too.

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