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Boiler DHW coil to gas water heater advice

Hi all,

Looking to plumb a DHW coil from a boiler to a Gas hot water tank. I was thinking of plumbing the coil to have isolation valves, a bypass and drains on the coil in case I needed to isolate it. From there the water can go directly from the coil to the house (mixing valve installed on that line as well as a relief valve), and also arrange the piping to go from the coil to the cold water inlet (or through the drain valve tap) of the gas water heater. Also install another mixing valve on the outlet of the gas HWH for anti scald protection (with a bypass for when operating in summer mode). Also going to add an expansion tank on the cold water supplies.

The idea is to run the boiler with the coil in the winter months with the gas HWH acting as a storage tank, and run the gas water heater in the summer months.



  • Steam
    Steam Member Posts: 45
    Sounds like a plan. Thanks a lot Hatterasguy.

    Take a look at my attached drawing. Let me know what you think.
  • Steam
    Steam Member Posts: 45
    edited September 2015
    Two mixing valves if one fails. I could eliminate it and keep the spare in the box, as there would be unions on the three connections of the mixing valve to facilitate easy change out. I like your idea better

    As for the coil bypass, that would be there if I have a problem.

    Modded the diagram

    Thanks again,