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Methanol as boiler antifreeze

JohnWood1 Member Posts: 63
I have used methanol in ground source heat pump loops as an antifreeze. (very common in that industry) It is relatively cheap, uses smaller concentrations than glycols for the same freeze protection and pumps a bunch easier when cold than glycol.

SO; Why don't we use it in radiant floor systems, or more to the point for snow melt? We now have "cold" systems that never see temps above 140F, so the idea of flashing should not be a problem.

Even if we did not want it IN a boiler for some strange fear of fire, if we use a HX to keep them separate it would make snow melt a lot easier.

What think you?


  • hr
    hr Member Posts: 6,106
    Sounds risky

    what if a relief valve would discharge? I'd think you would want to keep it far from any open flame, sparks, etc.

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  • JohnWood1
    JohnWood1 Member Posts: 63
    Flammability issue

    Actually glycol is flammable.

    Wonder if anyone reading this knows the flammability factors for 50% glycol/water vs 25% methanol/water mixes and would check in?
  • Lurker_2
    Lurker_2 Member Posts: 123

    Yes but what is the flash point of methanol vs glycol.

    I wouldn't want to be around 180 degree methanol when a relay kicks
  • J.C.A._3
    J.C.A._3 Member Posts: 2,981
    Just asking but ,

    How would plastic impellers and pex tubing stand up to methanol? I know most plastics will stand up to it....at room temps. but what happens when it's diluted in 190 degree water? Heat pumps use mostly metal impellers/scroll pumps and the like ,most of our circs use some type of plastic. Just wondering if that might be the case. Chris
  • hr
    hr Member Posts: 6,106
    Glycol is used in fire sprinkler systems so...

    it really isn't flammable, per say. However if it gets in the insulation around a boiler for example and the waters evaporate it can support a fire. I had this happen on a snowmelt boiler once that leaked from the air vent and wetted the boiler insulation. When the maintenance crew fired the boiler the insulation started to burn!

    Methanol has a 54°F flash point, highly flamable. it's classified as a hazardous waste upon disposal by the US Resource Conservation Act. Listed high in both acute oral toxicity and inhalation toxicity, and rarely found with inhibitors needed in hydronic systems. Just to many risks to be worth the cost difference.

    Plenty of other anti freezes out there calcium chloride can actually be inhibited for use in freeze protection, plenty of tractor tires with that inside :)

    Sodium chloride, potassium acetate (used in earlt PB snowmelts) Lithium chloride, lithium chloride anhydrous sodium chromate, glycerins, diethylene glycol and others have been tried and formulated for antifreeze solutions, mainly in fire protection systems.

    When all is said and done, propylene, or ethylene glycol still proves to be the best of the bunch, all things considered. Glycerin is still the choice for pVC systems as glycols can not be used with PVC piping.

    hot rod

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