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Question for Mark Eatherton

Mark, in a separate thread discussing my parallel reverse return system, you said:

"So, looking at it on the beginning, your supply would be 3/4" and the beginning of the return would be 1/2" because it is only carrying the flow of one radiator. Once the return picks up the second radiator, then it can jump to 3/4" because it is now carrying the flow of two radiators, Once you get to the second to the last radiator, the supply would drop to 1/2", again because it is only carrying the flow of one radiator, but the return stays 3/4" all the way back to the mechanical package."

My total supply main is 116 feet in length from boiler to last emitter (excluding branch emitter supplies). The distance from the next-to-last emitter is 40 feet, or about 36% of the entire main supply length. In my situation would you still recommend stepping down that last 40 feet from 3/4" to 1/2"? Would doing this add significant resistance, causing excessive head loss to the upstream supply?

Thanks

Comments

  • Not sure Mark is available this afternoon. Comments from any of the other pros are welcomed and appreciated.
  • Mark EathertonMark Eatherton Member Posts: 5,843
    Scott, it is important to maintain good "air sweeping" velocities in the hydronic system, within reason. In your case, where the mains are higher than the emitters, it becomes even more important to maintain these sweep velocities, otherwise the air will "hang up" in the vertical risers, and that radiator will eventually become air locked/blocked. The pressure drop of these 1/2" sections is fairly insignificant, because the flow rate through them is relatively low.

    It is a common practice for good reason.

    If you want to go to the trouble of having microbubble resorber air removal systems, and are going to be inducing oxygen scavengers in the fluid maintainenance program, and don't mind manually purging numeorus times in order to get all free air out, and can be assured that the chemicals will be maintained in an ongoing basis, THEN and only then could you consider running 3/4" throughout your mains. (I didn't thin so. Very few people maintian good chemical balances in thier systems. Set it and forget it is the American way.)

    No one EVER undersizes their pumps, especially on small, well balanced systems like you are designing. It may be hard to find a pump small enough to meet your needs, so your system will work fine.

    Sorry for the delayed response. I unplugged myself from the World Wide Web this weekend, in the mountains.

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
    SWEIGordy
  • Mark, thanks for the thorough response. I really appreciate it.
  • Mark EathertonMark Eatherton Member Posts: 5,843
    We are here to help! Please consider joining the RPA, where we can teach a LOT more and grow hydronics and radiant together.

    http://www.radiantprofessionalsalliance.org/Pages/Join.aspx

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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