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backflushing loop in new system

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hot_rod
hot_rod Member Posts: 22,151
compared to the others on the manifold. If it has multiple loops on the manifold try closing them down and check temperatures at the S&R of the suspect loop.

hot rod
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream

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  • David Roe
    David Roe Member Posts: 2
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    backflushing loop in new system

    My wife built a new home with radiant heat in concrete slab, and I have one particular loop that has a mind of its own. I have on occasion been able to get the loop to flow and heat up, but only for a short period of time. I've bleed the loop silly, and am beginning to suspect foreign debris, like a pebble or slug of concrete, raising havoc in the line. I'd like to try to backflush the loop in question, but don't have any specifics, having never done it.

    My questions are:
    -what pressure [psi] should be used?
    -should I use water or air?
    -Is the fitting at the manifold a regular garden hose thread?
    -I'll have to shut the supply line off for the radiant. Any other considerations?

    Thanks for any input
  • Brad White
    Brad White Member Posts: 2,398
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    Back-flushing

    This could be interesting...

    As far as medium and pressure, either air or water will do, so long as the pressure rating of the PEX is not exceeded. Even the pressure is dependent on temperature, meaning that if colder it will take more pressure. Hot water means lower pressure if that makes sense.

    My inclination is to use air first. When whatever it is lets go, you will have "some" water shooting across the room and hitting the cat, but if you use water entirely, Fluffy will take out a mob hit contract on you and watch. Ask me how I know.

    Also, with air, you can more easily get fittings, barbs and other connectors where you will be hard-pressed to do so with water.

    You should be able to isolate all of the other circuits. Most manifolds have built-in turn-cap valves.

    I would think 100 PSI would be plenty. It could well take more, especially those parts in concrete, but the parts above....??

    Make sure you know where the aiming point is. (Such a guy thing, the girls are always reminding us.) Let us know what you find.

    When done, re-fill with water the same way, to purge all of the air out after re-connection. As with other radiant zones, do these one at a time until the water runs clear. You should have plenty of velocity.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • David Roe
    David Roe Member Posts: 2
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    backflushing loop in new system

    Brad

    Thanks for the feed back. It was well received. How'd you know we have cats?

    I finally got around to the backflush and only got some black sediment/mineral deposts[?] with the air, and then flushed with water till clear. No big boulders. Everything seems to flow well in the loop with no notable obstruction.................The loop still doesn't heat up. I'm now wondering if a higher volume circulator[?] might help or have the loop leak checked. I'm defeated and lost.
  • Brad White
    Brad White Member Posts: 2,398
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    If there is no flow

    apparent in that one loop, David, see if the others are getting too much. It may be that you have double the loop length on this one thus the others have first-pick.

    If the above is the case, the longer loop has about 4 times the pressure drop as the others. Key would be to balance down (throttle) the other circuits so that all of them have the same total pressure drop. Try that and see.

    What you are possibly looking for is not higher volume but higher pressure (head) in your circulator. May be a combination of both, but let's say you have a Grundfos 15-58 (58 decimeters of head is what the 58 means). You may need a 26-99 (9.9 meters of head, a higher head circulator) by example only, to deliver the same flow rate.

    Balance first then let us know. Feed the cat.

    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
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