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Would you use this

bob eck
bob eck Member Posts: 930
For the contractors that use a indirect water heater with a condensing gas boiler (instead of installing a combi boiler) if there was a indirect water heater that doubled as a buffer tank would you use this type of tank?
One tank dose the primary secondary piping, adds water volume so the boiler will not short cycle when small zones are calling for heat and the same tank provides domestic hot water for showers and other use of hot water in the house.
Would you use a tank like this?


  • GroundUp
    GroundUp Member Posts: 1,924
    They make one (or more). Vitocell is a dual coil solar tank that can be heated via either coil and use the other one for a space heating draw while still using the DHW as normal. I'm sure there are more out there somewhere, and I have built a few using a regular tank and an additional external plate HX through the recirc or drain/relief ports- though not ideal the cost is much more attractive. What I have in my own house is set up like this, being charged with an outdoor wood boiler but powervent LP for backup in a regular old AO Smith 50 gallon WH with a plate HX through the recirc ports so when the tank cools, it brings heat from the OWB to charge the tank full of DHW so I can draw DHW as normal or draw my radiant off the plate HX, or both. Warm seasons without the OWB the powervent will take over and serve the same task.
  • hot_rod
    hot_rod Member Posts: 22,254
    Reverse indirect? TurboMax is commonly used this way.

    An external plate HX on virtually any tank will work and you can size them to the exact application, low approach for example.

    Good info on buffer sizing and piping here.

    Caution with dual coil tanks, the top coil will only get you a portion of what goes in the bottom coil :)


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 7,574
    edited November 2019
    The challenge can be doing all this with low water temps. My heat system averages < 110 degree for radiant. You cannot heat DHW at those temps. It would make a for a nice preheat though.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mattmia2
    mattmia2 Member Posts: 9,738
    seems like any indirect could do this with the right controls, run the indirect zone with a call for heat, dump the excess heat in the indirect or take it out, boiler fires when needed on the heating loop temp or on a dhw call with enough of a differential to make it run longer cycles, put a thermostatic valve on the dhw outlet, a bigger hx in the inderect would be better, would have to design your system to run with water temps above the dhw temp
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    The problem with any large indirect is the cost. Here in Maine, heat pump water heaters have a $750 rebate so pretty much every water (indirect or otherwise) gets replaced with a HPWH.

    Its certainly nice in the summer months to not burn any gas.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!