Any issues in using propylene glycol in a tankless?

Discussion in 'Tankless Water Heater Forum' started by dimprov, Mar 3, 2009.

  1. dimprov

    dimprov New Member

    Feb 3, 2009
    Austin, Texas
    Non-potable. Closed-loop hydronic system for heating. Exterior, wall-mounted unit.

    Any issues with performance, maintenance, warranties, etc.?

    If it matters, I'm gravitating toward a Rinnai. I'm dealing with meager data and unscientific anecdotes, but it points toward Rinnai as being one of the quieter brands. Apparently I'm one of the few that includes noise in their tankless purchase criteria, so there's not much to go on.

  2. SewerRatz

    SewerRatz Illinois Licensed Plumber

    Nov 20, 2008
    Chicago Illinois Licensed Plumber
    Chicago, IL
    They do make tankless boilers that is more than likely better suited for what you are planning to use it for. Here is one
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  4. dimprov

    dimprov New Member

    Feb 3, 2009
    Austin, Texas
    I'll assume natural gas, because that's my fuel source.

    Is it just my false impression or is the dividing line between tankless and boilers is starting to fuzz over? In its favor, a boiler clearly assumes you're going to recirculate the water, and so it doesn't ding your warranty if you do that.

    On the other hand, Rinnai and some other tankless units do allow recirculation, although it may reduce your warranty.

    Boilers are a lot heavier and a lot more expensive, and they often seem to assume an indoor location (or at least an enclosure), whereas many tankless are explicitly designed to hang naked on a wall outdoors.

    Regarding only equipment cost (not operating cost), the cost per BTU of hot water seems much lower with tankless. Some individual boilers are high BTU, but tankless manifolds can also do high BTU.

    I must be missing the big selling point for ng boilers because otherwise the world would be using ng tankless in place of ng boilers. What am I missing? I don't want to dismiss boilers out of ignorance.


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    Last edited: Mar 3, 2009
  5. dimprov

    dimprov New Member

    Feb 3, 2009
    Austin, Texas
    I just spoke to Navien. They said not only do they not ding your warranty if you recirculate, but their unit comes with a recirculation pump already built in.

    The built-in buffer tank is 1/2 gallon, which they said is enough to prevent cold water sandwich.

    I asked for a copy of the warranty, and they're mailing it to me. I should get it by Monday.

    They said the exhaust air temperature on a Navien is 80F, versus (they said) 400F for a Rinnai.

    The required clearances to combustables is lower than for a Rinnai. 4 inches in the front for Navien, versus 24 for Rinnai. 1/2 inch on the side, versus 6 inches for Rinnai. 1/2 inch in the back (requires a special mounting bracket to offset), versus zero inches in the back for Rinnai, so score one for Rinnai. 12 inches required clearance beneath for Navien.

    They said any licensed plumber can install the Navien without it affecting the warranty, whereas Rinnai told me that not just any licensed plumber will do--the plumber has to be Rinnai certified, or the warranty is invalid. That's a bit harsh. Does Rinnai assume licensed plumbers are stupid?

    Navien says their units are more expensive than Rinnai, but that the cost gap closes when the circulation pump and simpler venting are factored in.

    Navien sounds great in theory, but it's so new there is no local track record. There aren't even local installs to go see.

    Navien sells only to wholesale.

  6. Master Plumber Mark

    Master Plumber Mark Sensitivity trainer and plumber of mens souls

    Feb 6, 2005
    Sensitivity trainer.. plumber of mens souls
    indianapolis indiana - land of the free, home of
    Glycol breaks down

    I remember with the glycol systems in solar panels
    that the glycol would break down every few years and have to be changed out..

    of course that is not a big deal to change the stuff out ....

    but I would be leerey of it all and I would find out directly
    if the o rings and other seals in the pumps would break down becasue of the glycol...

    I suppose that the glycol will heat up in the exchanger just like any other fluid will...
    I do not know what type of residue it might or might not leave behind in the heat exchanger

    which basically you are turning your tankless into something akin to a glorified car radiator...
    Last edited: Mar 5, 2009
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