"Garn drainback" feasible?

pybyr Posted By pybyr, Aug 29, 2009 at 1:57 AM

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  1. pybyr

    Minister of Fire

    Jun 3, 2008
    Adamant, VT 05640
    Some friends whose woodstove has expired have indicated an interest in a new efficient wood boiler, and tying it into their HW baseboard heat. I have a downdraft boiler myself and am completely happy with it, but for various reasons, I think a Garn in a nearby outbuilding might suit them especially well. I've seen various descriptions of Garn installs with a plate HX between the Garn and the heated spaces, where some of the heat zones are above the Garn. What I am wondering is: just as some do "solar drainback," could one do a system where at least the 2nd floor of the heated space did not rely on the boiler system to stay full of water at all times, and, rather, relied on pumping to get water and heat up there as needed? Seems as if it might simplify things- if it's suitable?
  2. Como

    Minister of Fire

    Jan 28, 2008
    I can think of all sorts of problems, if they are concerned about freezing glycol would be the answer.
  3. tom in maine

    tom in maine
    Minister of Fire

    Apr 4, 2008
    Searsport, Maine
    It can be done, we have done it many times.
    The potential problem is when the tank or Garn is hot, and you are pumping up to a second floor, there is the potential to flash the water to steam in odd circumstances when the water returning to the tank might find itself under a slight vacuum.

    This is very cool, but can make ungodly noise (always at 3am--in my case) but the subtle physics is kind of amazing. It can continue to induce flow after a circulator shuts off, sometimes even with a check valve. I thought it was a lot of fun and interesting, except it sounded like clanking steam lines.

    At very least, there will be water noise, which is not always appreciated.
  4. Gooserider

    Mod Emeritus

    Nov 20, 2006
    Northeastern MA (near Lowell)
    Sounds like you are wanting to run a system non-pressurized? If so, in addition to the issues that Tom mentioned is the concern about 02 in the plumbing - and the potential for corrosion it induces... This is probably the biggest reason why the typical Garn install uses a heat exchanger - it allows the non-pressurized open Garn to work with a pressurized heating system. One can design a system that will work as an open system, essentially by eliminating all ferrous metal components, but it makes the design more difficult as many common parts may be harder to come by in copper or brass, and will cost a lot more...

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