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Dual Coil Solar Water Heater Recommendations

Wellness Member Posts: 138
Can anybody recommend a Dual Coil Solar Water Heater with electric backup? I currently have an 80 gallon indirect heater fired by a boiler and a separate single coil, 100 gallon solar heater with electric backup. But, due to space limitations, I want to eliminate the indirect heater. I've been looking at the Dunkirk H2O115DE but I was wondering if there were any other models out there I should consider.


  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    Dual coil tank

    The Viessmann B-79g Vitocell 300 is the best, and the only 316Ti SS on the market. I've seen an electric element installed on the man hole cover,(by installer, not Viessmann) for those wanting electric backup.
  • SWEI
    SWEI Member Posts: 7,356
    edited January 2014
    Is this a DHW system?

    How big a tank?  How much collector area?  How much sunshine there?

    It's generally best to provide backup heat outside the tank to maximize collector efficiency.  Think of the solar system as a preheater, with the backup source sized for the worst case solar tank temp instead of groundwater temp.  You'll be pleasantly surprised at the increase in flow rate that yields.  Believe it or not, tankless electric can work quite well for this if the answers to the above questions are right.

    Dejong Tank (a Dutch company) makes very nice stainless dual and triple-coil tanks.  Crown Boiler sells some models here; Radiant Engineering up in Bozeman handles the 240 gallon models http://www.djg.com/en/standaard-producten/solar-750-en-910-l/
  • Wellness
    Wellness Member Posts: 138
    edited January 2014

    I'm in the DC area. I don't know the specs on the solar collector because I didn't install it. I think it's a 30 tube Vacuum Tube unit model. My experience has been that my indirect boiler heats up the 80 gallon indirect tank really quickly in the winter. In the summer we shut off the boiler and get more than enough solar hot water so long as it's not cloudy for long periods of time. My main goal here is to create more space in the utility room to accommodate another project.
  • SWEI
    SWEI Member Posts: 7,356
    A dual-coil tank will work

    but you won't get much solar fraction during winter.  If you're looking to recover floor space from the indirect, you might consider following the solar tank with a gas-fired tankless.  Be sure you pick one that handle solar preheat, then pipe the tankless after the tempering valve and set it ~5ºF lower than the valve.  Even in the dead of winter, the solar tank should be at least 70ºF, which will take a whole lot less energy to heat than groundwater will.