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Air in heating loop for indirect tank

Brian S
Brian S Member Posts: 12
Looking for help on a heating system we service, where a couple times a year the heating loop for the indirect tank will get air bound. Oil-fired heater with multiple fin tube baseboard multiple loops and 32 gallon indirect tank. Has an air eliminator and bladder style expansion tank. Only happens to the indirect loop and not any of the other heating loops.
Pump on the indirect loop is a 007 with 3/4" piping. Is the air eliminator somehow bringing air into the system? I will provide pictures of the piping soon if needed.


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    If the air eliminator is on the indirect, it should be doing the job. It's also possible due to the piping, that air is coming in from somewhere else, but heading to the indirect and staying there because it's nice and big and slow.

    There was an error rendering this rich post.

  • Brian S
    Brian S Member Posts: 12
    Air eliminator is on the heat main just upstream of the tees for indirect and main heating pumps
  • Brewbeer
    Brewbeer Member Posts: 616
    edited November 2018
    The indirect may have large diameter internal piping, and with only 3/4 inch feeding it, flow velocities in the internal coil could be too low to capture and move the air. 8 GPM in a 3/4" pipe is 5.8 fps, in a 1" pipe it is 3.3 fps, and 2.1 fps for 1 1/4" pipe.

    For systems that have the air eliminator on a heating leg which only sees flow during the heating season, sometimes it is recommended to install a dedicated air eliminator on the indirect loop.

    We like photos.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
    EBEBRATT-Ed Member Posts: 15,628
    The 007 should have plenty of push with only 3/4" pipe the water is flying through their pretty quick. It should be moving the air back to the main system without a problem. Pics will help
  • hot_rod
    hot_rod Member Posts: 22,261
    I wonder if something is preventing the air separator from working properly. It might be good to remove the top of it and make sure is is not stuck or plugged.

    Do you ever hear air coming out of it when you get them indirect flowing?

    The float auto vent should not be an issue, but try closing off the cap on it.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream