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Air in hot water loop

Dave_61 Member Posts: 309
We just bought an older home that has oil fired steam heat. In a section of the house that originally had no heat, they had installed a forced hot water system with baseboard radiators. It is supplied through the coil that was originally used for DHW in boiler.

The piping between the radiators is a grey plastic with 90 degree brass fittings where the tubing goes through the floor. The brass elbows are flat on top.

There is no vent for air. When it is on, you can hear the air rushing through the tubing. It heats fine but is noisy.

I purged the air by filling the boiler and letting water out of the boiler drain valve (pushing air through system). But now it's back again.

Would it be possible to add an air vent by drilling and tapping one of the brass elbows and putting in a vent?

Thank you


  • Ironman
    Ironman Member Posts: 7,379
    Can you post a pic of the boiler, it's near piping and where you're filling and draining it?

    I'm not quite following your description because filling a steam boiler has no effect on the domestic coil as far as getting water into it.

    The gray pipe is probably Qest and should not have been used for hydronic lines.

    I would not recommend trying to tap a Qest fitting.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    HVACNUT Member Posts: 5,865
    edited November 2017
    You've basically have a hydronic heat exchanger, and should have a pressure reducing valve, extol tank, air elimination, circulator and a purge station.
    Can you post some pics?
  • Danny Scully
    Danny Scully Member Posts: 1,427
    What I’ve found to happen sometimes is the water in the coil actually begins to boil, thus creating air. You might need a mixing valve as well.