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connect on demand water heater to an indirect tank?

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jrv8984
jrv8984 Member Posts: 45
edited September 2019 in Domestic Hot Water
Is it possible, advisable. I would prefer to use my 70 gallon indirect tank year round instead of having a tank for the summer and using the coal fired indirect for the winter? So if I could just hook up an on demand to my indirect tank it would make things simpler.

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  • JohnNY
    JohnNY Member Posts: 3,231
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    I've done it. You don't have to go through the indirect tank's heat exchanger/coil. Just connect the gas-fired tankless water heater to the domestic side of the indirect as if it were a domestic hot water source and a storage tank, which is exactly what it is.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
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  • JohnNY
    JohnNY Member Posts: 3,231
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    You'll need changeover valves and someone to run the tankless heater through a cycle or two once a month or when it's not in constant use. This is how we address hot water in buildings where they want to take advantage of "waste heat" left in the boiler in winter and run a smaller appliance in warmer months.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
    Classes
  • jrv8984
    jrv8984 Member Posts: 45
    edited September 2019
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    How would I size the on demand unit to feed the 70 gallon indirect tank?
    It would only be used 4-5 months a year over the summer, otherwise it would be turned off.
  • jrv8984
    jrv8984 Member Posts: 45
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    anybody?
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,331
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    Hi, You could probably use the smallest tankless unit you can find, as long as your draw is something less than 70 gallons.
    Yours, Larry
  • Poppasmurf
    Poppasmurf Member Posts: 5
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    You would size it according to the expected demand. If you have one bathroom and one kitchen- it would be quite different from say 3 bathrooms 4 bedrooms with 3 teenage girls.
  • mikeg2015
    mikeg2015 Member Posts: 1,194
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    Rather than a tankless, why not a “summer boiler”? Get the smallest condensing boiler you can find and connect it to the primary loop. It also will be a backup in case the main boiler fails and can carry the building in shoulder season.