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Hydronic radiator valves: Holes inside myth?

IamNotARobot Member Posts: 1
I am still relatively new to the industry and just started a full time job in it. One question I can't seem to get to the bottom of is holes in hydronic radiator valves. There are a few persons in the business that have told me that you can't truly close a hydronic radiator valve because there is a small hole in the valve to allow some water to pass through to prevent freezing. My teacher at school, who works in the business, says it is a myth. Personally I think it is a myth too, but there are old folks that been doing heating for years that swear it is true.


  • Danny Scully
    Danny Scully Member Posts: 1,425
    JUGHNE Member Posts: 11,061
    The old valves I have seen on gravity systems were 1/4 turn "spool" design with a small opening when 100% "off".
    Freeze protection for the rad and any piping installed in an outside wall, IIRC. Plus without this small flow just getting the heat started to that rad may have taken too long.

    Now if you replace one with a steam valve, you would lose the small hole flow for sure.
  • Lance
    Lance Member Posts: 270
    First lesson not taught in school is you are responsible for your own education. Second lesson not taught in school is teachers don't know everything even though they speak as if they do.
    Standard practice is always ask for a steam valve when using steam and a hot water rad valve when hot water. One of the reasons is that little hole. Of course the counter guy can be like a teacher and not know everything so we have to. The difference between hot water and steam valves is the hot water valve has a hole drilled in the stopper to permit a tiny amount of flow. It can be a form of freeze protection should it be in a cold room. However if btu loss in room is greater than heat supplied freeze can still occur. Found: Transactions of the American Society of Heating and Ventilating ..., Volume 2 which I paraphrase states: "Many Mfgs are now putting a small hole in the seat of their valves to prevent freezing, my experience is it permits sufficient circulation to keep radiator as hot when valve is closed as if it was open. Another fitter had a customer complain he could not shut off the heat when valve was closed. Made him solder the holes shut before final payment. I do not think the practice is a commendable one as it causes the fitter trouble and annoyance."
    Knowledge is power and money if used wisely.
  • Jackmartin
    Jackmartin Member Posts: 196
    I never fail to learn something on this site thank you. Jack Martin