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Thread: How to purge air from hydronic home runs

  1. #1
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England

    Default How to purge air from hydronic home runs

    I have 4 in-floor radiant loops that run off of manifolds in the basement (each about 200' long of 1/2" pex). It's using a Wirsbo (Uphonor) manifold with individual zone valves into the manifold. A single circulator pump and a mixing valve to adjust the inlet temperature. Since this is in the basement, all of the loops are higher (three on the first floor, and one for the bathroom on the second).

    The system also feeds a hydro-air heat exchanger in the air handler (mostly used for backup - was the original primary heat). This has it's own pump.

    It has a check valve and air extraction, but I regularly have a problem during startup getting all of the zones to circulate. Since they are home runs, air (it shouldn't get it) accumulates at the high points and is difficult to extract. I've got 3 of the 4 loops running. The one (on the first floor) that is under where I usually sit doesn't seem to get any flow and on these cold days (going to get below zero the next couple of days) will be more of an issue. When it's working, even at an indicated room temp of 68-degrees, the room feels warm. When it dosen't work, even though the room temp is the same (the hydro-air backup turns on), it feels uncomfortable.

    How does one actually purge air from a home run loop? The system does have an auto-fill valve. I've tried various things about closing certain valves opening a drain valve (there are two, one on one of the manifolds and another on the return) and allowing the autofill to over pressurize and get some air out, but it still doesn't flow in that one loop. 3-out of 4 is okay, but not ideal!

    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  2. #2
    DIY Member edlentz's Avatar
    Join Date
    May 2008


    I have a hydronic in floor system. I have only had to purge the air only when I made some changes. I suspect that if you shut off the flow on the zones that are flowing and open the drains it will eventually purge tha air bubble. I had a DIY towel warmer and it took about 15 minutes to get all the air out of that sucker. I think you need to be more patient and it should work out.

    Good Luck


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