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Adding antifreeze to old boiler

karter
karter Member Posts: 59
in Radiant Heating

Got 5 gal of sentinel 500 and 2 5gal of RHOGARD RTU-30 want o set it at 20 below I know the sentinel is consatrated 50x50 work? What about rtu-30 is it premixed or do I need to add water to it . This way I know how much water to drop out of my system.

Comments

  • pecmsg
    pecmsg Member Posts: 6,453
    edited September 20

    why do you want antifreeze?

    And WHY -20*?

  • hot_rod
    hot_rod Member Posts: 25,649

    there are 3 temperatures to know with glycol

    Freeze point, ice crystals start to form

    Slush point, no longer able to be circulated

    Burst point, fluid turns solid , may cause pipes to burst

    DowFrost HD has a burst of -30 at a 35% blend

    It is uncommon to need a 50%

    Temperature protection varies a bit from brand to brand, sone brands show 3 temperature others just two

    Here is Dowfrost and Dowfrost HD

    IMG_1060.jpeg
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • karter
    karter Member Posts: 59

    Old home old oil burner boiler changed to nat.gas 3 zones 3 pumps have copper in basement floor radiant heat. Base board 1st floor 1 room. 1/2 copper in ceiling covered in vamiculike and caped with 3/4 plywood 10 in fiberglass on top of that. Last winter fought system to stay running when it got below 0 . My fault had a pump go bad had no shutoffs to help change it so had to dump water out.im color blind so didnot see that water had antifreeze in it.changed all pluming to pumps now have shutoffs above and below the 3 pumps. Have bought the 5 gal of the sentinel 500 .and 2. 5gal pails of the RHOGARD RTU-30 ..not shure how much water to add to them .I know system holds way over 30 gal dump the water in a 30 gal drum but was way more than that. Fig I would pull 30 gal water a d replace with the antifreeze.

  • GroundUp
    GroundUp Member Posts: 2,416

    The Rhogard is only 30% as-is and the Sentinel doesn't seem to show anywhere what its concentration is, but by the burst temp I would guess around 40%. The only way to do this properly is to get your hands on a refractometer and make adjustments as necessary, but you almost certainly don't have enough to keep the total concentration above 25% where it needs to be. With that said, why do you want glycol at all? If this space is occupied, it's not going to freeze and there is no reason to mess with glycol.

    PC7060
  • pecmsg
    pecmsg Member Posts: 6,453

    remember the more glycol the less heat transfer.
    As said get a refractometer and keep the freeze point around +20*F.

    PC7060
  • karter
    karter Member Posts: 59

    Had it gell up at 10- shuts the system down with no flow .with pipes in attic and basment floor its a no win deal without something

    GroundUp
  • pecmsg
    pecmsg Member Posts: 6,453

    did it freeze and burst?

    If the circulator is running it’s generating heat!

  • karter
    karter Member Posts: 59

    Gelled up had to crank heat to 90 to keep it running

  • hot_rod
    hot_rod Member Posts: 25,649

    You need to know exactly what fluid brand and model you have to get accurate information.

    Comparing RhoGuard to RhoGuard ultra at 40% the freeze point is quite different. The Ultra should be pump-able well below 0°F

    Rhomar doesn't show a slush point, that is the temperature where is no longer flows via a circ.

    I used the RhoGuard Ultra as it was a multi metal product

    When you blend on the jobsite the final % is often lower as you tend to s add straight water as it purges air out. Best to check with a refractometer a day or so later after it blends well and deareates

    Screenshot 2025-09-21 at 2.52.49 PM.png

    Keep in mind the pumping penalty with rich mixes, here is what 50% can do to a basic hydronic loop.

    Screenshot 2025-09-21 at 10.02.45 AM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • karter
    karter Member Posts: 59

    Its rtu30 thogard

  • karter
    karter Member Posts: 59

    Ok can I getaway with this I have 16 1/2 gal of antifreeze. Can I dump 16 1/2 gal of water out btm of boiler and using my small transfer pump pump the antifreeze in and then start up all 3 boiler pumps and let it mix.

  • nate379
    nate379 Member Posts: 91
    https://forum.heatinghelp.com/discussion/comment/1865567#Comment_1865567

    Anytime it gets cold here, plumbers and HVAC guys are super busy with dealing with frozen heat pipes.

    My neighbor had a zone in his floor heat freeze one winter... in a heated house that wasn't freezing.

    GroundUp
  • karter
    karter Member Posts: 59

    Yep I'm older and my wifes not good health so I'm trying to keep from having a prob like last winter

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