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.

thermal flow from indirect DWH

I've got a triangle tube smart 40 indirect DWH hanging on its own secondary loop off of a caleffi hydrolink hydraulic seperator. These have the Boiler water in a jacket arround the water being heated.

Circuit goes from Hydrolink to pump to check valve to DWH input on lower tank conection then out upper tank connection and back to hydrolink.  Because the smart 40 holds several gals of hot boiler water and supply loop returns from the higher connection on the DWH, when the circulator is off  it seems seems like I get some thermal cycling flow out of the DWH and up the secondary pipe back to the Hydrolink. I say this because it seem like a possibility and I've observed the DWH cooling off quicker then I would have thought. Check valve in input won't prevent this.

Is this a possibility? Would another spring check valve on the return pipe provide just enough resistance to stop this flow when the circulator is off? If so, do I keep the check valve on the input too?

I was neven sure if/why one needed a check valve for loops off of the hydrolink (or any closely tees type connected secondary loop. Put one in because a Callefi example drawing showed one.


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I have a different boiler and indirect, but...

    ... there may be enough similarity. My system is basically prrimary-secondary as far as heating the house is concerned. But the indirect (W-M Plus 40, that may be the same as a Smart-40; mine was made in Belgium) is across the boiler supply and return pipes in the primary circuit. The supply goes into the bottom of my indirect. There is a Taco 007-IFC at the top of the indirect that pumps the somewhat cooled water back to the return of the boiler. These pipes are pretty much horizontal and 1-inch copper. I put 1-inch black foam insulation on those pipes because they heat my garage more than I think it needs. ;-). Near the indirect, the pipe drops about 4 or 5 feet, so there is not likely to be undesired circulation that way. The return has the IFC gizmo in the circulator. For my system this is enough to prevent unwanted circulation when the circulator is off. The boiler manufacturer suggests a real flow-check valve instead but my contractor said it was not needed, and it seems to be true.

    I also put similar insulation on the 3/4 inch supply to the domestic side and the delivery as well. These qet quite hot, even when there is no demand for hot water for the first several feet. There are no flow-check valves in the domestic side, but both supply and delivery drop over 5 feet, and that seems to prevent undesired convection flow. But the conduction through the copper tubing is an issue that called for insulation.
  • Gordan
    Gordan Member Posts: 891

    If the hydrolink is above the indirect, and you have fairly big piping between the two (which is likely), then gravity flow can occur even on a single pipe. The check valve may prevent it from occurring on the supply, but it will still happen on the return. A thermal trap would prevent this from happening.
  • tbone52
    therm flow

    I was wondering if a spring type check valve on the return might have enough resistance to stop the thermal flow?
  • Gordan
    Gordan Member Posts: 891

    Not a swing check, mind you, but a spring check.
This discussion has been closed.