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Best way to heat trap/stop gravity flow in indirect

I have a Heat-Flo SS 115gal indirect that I heat with my wood gasification boiler.  I bought the large size so I'd be able to go for 2-3 days between firings of my boiler during the shoulder season, as I don't need much heat in the house in the fall/spring.  That said I can get the indirect up to 180 on the bottom so there is a lot of hot water stored.  I was in contact with Heat-Flo and they said it was permissible to heat the tank to this temp.  I mix the water to 120F with an ASSE mixing valve which is properly heat trapped about 24" below the hot outlet.  The way the mixed pipe rises after the mixing valve it produces a gravity loop between the hot outlet and the valve and back to the cold inlet of the tank.  I insulated all of this piping but the hot water migrates into the cold supply for the house and tempers the cold water for a few seconds when opening a faucet.  Also this pulls quite a bit of heat out of the indirect.  I've closed a ball valve during a period of 24 hours and the tank temp only dropped about 10 degrees, but wit it open it drops about 30 a day.  This seems to indicate that most of the heat is escaping through this gravity loop and taken to the cold line and being dissipated every time a cold water draw is initiated.  What is the best type of heat trap, a swing check or would it be noisy during small draws?  I was wondering about installing a 1/2" swing check in the vertical outlet of the water heater?? The ones with the little rubber flaps in them don't seem like they would hold up in the long term.  I'm open to any and all suggestions.  I can post a picture if that'd help.  Thanks Pros!  BTW this is in my own house. 

Taylor<em>  </em>
Serving Northern Maine HVAC & Controls. I burn wood, it smells good!

Comments

  • SWEI
    SWEI Member Posts: 7,356
    cold water check valve

    Do you have a check valve in the CW supply line already?  We use a quality spring check right after the CW supply shutoff.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,303
    What about thermal expansion?

    Wouldn't the expansion of the water force the relief valve to open?  As it is now, I valve off the hot outlet during a fireing and the expansion of the cold water forces itself backward through the CW pipe and ultimately the well tank absorbs the expansion.  I was thinking of using a brass spring check on both the HW and CW lines to keep the heat in, but the expansion thing came to mind.  I could put an expansion tank on, but it seems like a waste.  I was thinking of drilling a small hole in the CW check to allow a small amount of back-flow to the well diaphragm tank.  I just don't want to risk it plugging, I am open to any ideas.  I guess the worst thing that could happen is popping the relief valve, but I don't want to rely on that as my safety.  Thanks guys!



    Taylor
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • SWEI
    SWEI Member Posts: 7,356
    Thermal expansion tank

    Goes on the CW side, downstream of the check valve.  Put a service valve on it so you can test/replace it later.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Would a flow check valve work?

    I am a homeowner, not a heating professional.

    But it occurs to me that a flow check valve would do the job.

    One like this:



    http://www.taco-hvac.com/en/products/Flo%20Chek/track_file.html?file_to_download_id=15472
  • SWEI
    SWEI Member Posts: 7,356
    Flo-Chek

    Will work fine as long as you buy the bronze version and mount it horizontally.  It will also cost 3-4x what a spring check does.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,303
    I used a spring check all is well.

    Thanks!
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
This discussion has been closed.