Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Using Buffer Tank With Internal Coil To Preheat Incoming Water To Electric Water Heater.

I am told that the desuper heater circuit on a water to water geothermal heats water to the 120 degree area not hot enough for me. Therefore I am thinking I would like to have a 80 or 110 gallon buffer tank heated by the water to water geothermal with 1" fittings in and out that would allow the geothermal to heat water in the tank (as a buffer tank). Then I would like an internal coil in the buffer tank with 3/4" fittings that would have enough surface area to preheat water to the cold side of my domestic electric water heater as to allow it to top of the last 20 or 30 degrees. This would accomplish three things number one it would not require a geothermal unit with a desuper heater, it would greatly increase the amount of domestic hot water available and it would capture as much of the efficiency possible from the geothermal unit heating both domestic hot water and zone heat. My question is does anyone build a buffer tank with a coil to accomplish this? Most tanks are built as domestic hot water tanks that use the coil with 1" fittingsto be heated by a boiler to heat the domestic hot water which has 3/4" fittings.
Does anyone build such a tank? Heat Flo makes a stainless steel tank with stainless steel heat exchange coil but again it is designed to heat domestic with hot water or steam from a boiler thru the coil. (Heat-Flo 316 Stainless Steel Indirect Water Heater Tank with single heat exchanger 80 Gallon - HF-80)
Any help here would be appreciated.
Am I thinking wrong here? Would this not be a simple design?


  • hot_rod
    hot_rod Member Posts: 22,256
    You need a lot of surface area for that concept, An external plate HX is one option, with a blank storage tank, or a reverse indirect like the TurboMax.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • icesailor
    icesailor Member Posts: 7,265
    Electric water heaters have two 1" tapping's in them for electric elements. The rest are all 3/4". The drain is 3/4".

    How you use the tapping's is your choice.
  • Rich_49
    Rich_49 Member Posts: 2,766
    Dunkirk makes a buffer tank , options for a coil at top or bottom .
    Well made , have used these myself for various needs . Good tank
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
    Turbo Dave