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Checking Glycol

Housedoc Member Posts: 66
Does anyone have a recommendation on a hydrometer or similar device to check the freeze protection of propylene glycol and distilled water in a a solar water heater? There are all kinds of fancy kits that measure PH and specific gravity. They are $500 or more. But there must be a cheaper alternative. Any ideas ????


  • nmsolarken
    nmsolarken Member Posts: 6


    I just bought a refractometer for testing the freeze point of my glycol/water mix.  For PH I think standard test strips ought to work fine.  A search for glycol refractometer will return several results.  I can't speak for any specific model but I have tested the inexpensive one I just picked up on a couple sample mixtures and it worked well.

  • hot_rod
    hot_rod Member Posts: 22,251
    a Ph stick meter

    is what you want. You should be able to pick one up for 100 bucks or less. I like the Hanna brand.

    Really you should not need to check the freeze protection every year, unless you add water or more glycol it will not change.

    The Ph is important. I would test that yearly to start. If you notice the PH level dropping you need to find and fix the cause. Often times it is caused by excessive over heating of the glycol. A stagnant (no flow) collector can exceed 325F. Solar glycols can stand an occasional over-heating, but not on a daily basis.

    Check the label but the new glycol may be 10- 11 ph. if it drops into the 7's it may be time to boost the inhibitors or drain, flush and replace. and fix the cause of the over heating.

    Some causes would be lack of load on the system, power outages, improperly programed control, etc.

    Freeze protection can be tested with an inexpensive automotive tester. Some of the new cars now use propylene glycol as their coolant, and tester will read both EG and PG. If you test glycol for a living a refractometer is worth the money.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Cheapest Way

    Here's how Thermomax describes a glycol test:

    "- To check antifreeze/inhibitor concentration, draw off a small sample at the drain cock and place in the freezer compartment. Remove when frozen then measure temperature at “slush” stage i.e. when ice and liquid are both present. Temperature should be the same or lower than the minimum expected for the locality."

    Extra credit to the first Wallie who identifies the problem with this procedure.

    There was an error rendering this rich post.

  • Slimpickins
    Slimpickins Member Posts: 339
    I think

    the answer is most household freezers don''t go low enough to freeze at say, Denver's lowest expected minimum temperature.
  • Is_solar
    Is_solar Member Posts: 10
    $30 hydrometer

    I ve had a $30 hydrometer that i got on ebay 5 years ago.  Still working great.
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588

    But if you live in an area that never sees subzero F temperatures, it's a more "definite" way of checking the freezing point, and can be used to make sure that your $30 hydrometer is telling the truth.

    There was an error rendering this rich post.

  • Karl_Northwind
    Karl_Northwind Member Posts: 139
    reserve alkalinity test

    I use the PH Strips and a refractometer on a regular basis for most service calls, but on larger jobs than DHW, where the cost of replacing antifreeze is substantially more than a return visit, I have our local chemical company do a reserve alkalinity test.  it's essentially a titration that tells us how much buffering capacity is left in the antifreeze. 

    I don't think they charge anything, or maybe $20.  but we buy all our antifreeze there, so that helps.

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