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connect on demand water heater to an indirect tank?

jrv8984jrv8984 Posts: 41Member
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.

Comments

  • JohnNYJohnNY Posts: 2,388Member
    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.
    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is the Boilers and Hydronic Heating Systems Course Instructor at NYC's Mechanics Institute, a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
    John also oversees mechanical installations and maintenance for metro-area clients with his family's company, Gateway Plumbing and Heating along with his brother/business partner.
  • JohnNYJohnNY Posts: 2,388Member
    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.
    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is the Boilers and Hydronic Heating Systems Course Instructor at NYC's Mechanics Institute, a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
    John also oversees mechanical installations and maintenance for metro-area clients with his family's company, Gateway Plumbing and Heating along with his brother/business partner.
  • jrv8984jrv8984 Posts: 41Member
    edited September 2019
    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.
  • jrv8984jrv8984 Posts: 41Member
    anybody?
  • Larry WeingartenLarry Weingarten Posts: 1,649Member
    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
  • PoppasmurfPoppasmurf Posts: 5Member
    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.
  • mikeg2015mikeg2015 Posts: 1,063Member
    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.

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