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Dish soap to ‘eliminate’ air

I have a coworker who considers himself somewhat of an expert on everything relating to HVAC. Recently on a boiler job while having issues with eliminating air in the system because of the failing auto air vent, I recommended installation of a micro bubbles resolver (a spiri vent) and noted that I would have installed one if I was doing initial install on the system he claimed that he didn’t think they were necessary and told me his trick to eliminate air bubbles was to use Dawn dish soap. I’m curious how many other people use this trick. He went out to his truck got a bucket and pump and some dish soap added to the system and while it did quiet the system down I never saw more air come out of the vent meaning that those bubbles were just suspended in the system and not actually eliminated. What kind of failures do you see when that is considered the ‘remedy’ to air in the system instead of a properly installed piping layout?


  • hot_rod
    hot_rod Member Posts: 21,844
    really should not need to resort to soap to clean air out. It sounds like the soap he added is creating then bubbles for you to see coming out:)
    One concern is air continues to come out of solution and go back in as fluid is heated and cooled, so you want an good purger that works all the time, not just a single injection.
    Excessive soap will change the ph and could cause issues also.
    You are right to suggest a microbubble type air elimination device.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mattmia2
    mattmia2 Member Posts: 9,410
    I have left dish detergent on iron fittings I was testing for leaks. You don't want to leave it in the system. It caused the black iron to rust.