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Inslab piping above manifold

hr Member Posts: 6,106
I remember a contractor that would use only 3/4 PB for his radiant jobs, back in the day of PB :)

Problem was on jobs with small rooms and zones he would get down into the 150 foot or less loop lengths.

With that diameter tube his flow rates were very low, and with it his velocities. When you get down around, or below 3fps the fluid doesn't carry the air with it very well. it was extremely hard to purge and keep those low velocity zones air free and quiet.

Good purge points for the initial fill, and a properly placed air elimination device, along with good fluid designs always results in a dependable, noise free, air free hydronic system.

hot rod

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  • Chris_91
    Chris_91 Member Posts: 5
    Inslab piping above manifold

    Hello All,

    Long time reader, first time poster.

    I'm having an argument (discussion) with a plumber with many years of experience in hydronics.

    For an inslab job, the radiant PEX piping is shown in the slab _above_ the manifold. For air control a seperator is located on the supply to each manifold, and an automatic air vent is located on each return (a little overkill?).

    My friend and mentor believes that this will still result in air problems because:

    You can't pump air!

    He believes that the system will air lock, and without a manual air vent located at the highest point we'll never get the air out.

    My thought is there must be thousands of square feet of radiant installed above manifolds... why don't they have air problems in the tubes?

    Any thoughts?
  • ALH_4
    ALH_4 Member Posts: 1,790
    No Problem

    Done it many many times. If the zones are purged well initially, it is not a problem. I recommend using a Caleffi Discal, Spirovent, Honeywell Powervent, or equal on the main distribution piping. One vent should easily handle an entire home.
  • Al Letellier_9
    Al Letellier_9 Member Posts: 929

    I agree with Andrew that it will be no problem. As long as the pump is properly sized and "pushing" you will experience no trouble with air. We do it that way most of the time. I still prefer the manifold above the tubing, put this isn't a perfect world. Pardon the pun, but go with the flow!!!
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