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Hydraulic separator, Closely Spaced Tee needed for single zone system?

willpar
willpar Member Posts: 2
in THE MAIN WALL
Hello all, I am looking at replacing a very old boiler system with the Rinnai i120SN (heat only) unit. It's currently a single zone (with a split going to each side of the 2200 ft2 house) but no valves and only one thermostat. Current system is only a single pump for the boiler on the return. Do I need to install a hydraulic separator/CST in this system and a separate boiler and system water pump? Or just install the pump going into the unit? Installation instructions all indicate the use of the Closely Spaced Tee needing to be used. If so, I would need to reduce from the 1 1/4" combined return line down to the 3/4" line going into the unit. Likewise, the supply piping is 1 1/4 before the split and would need to be reduced coming out of the unit. I will replace everything else, air separator, expansion tank, dirt separator, PRV, fill valve, backflow preventer. Thank you!

Comments

  • hot_rod
    hot_rod Member Posts: 24,915
    With a hydraulic separator you will get excellent air, dirt, magnetic, and hydraulic functions 

    3/4 from heater to sep
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    willparMad Dog_2hilltownEdTheHeaterMan
  • willpar
    willpar Member Posts: 2
    Thanks hot_rod. Was going to keep the 1 1/4" supply line already in place and keep the air separator/expansion tank there and put the dirt separator in the 1 1/4" return line before the heater. My understanding is the wider the pipe, thus lower linear flow through the pipe the better the air separators work? I'm planning on using a Grundfos UPS15-58FC for the boiler pump and I guess for the system pump now. The low speed should be sufficient for flow spec but I'll have the ability to increase if need be.
  • hot_rod
    hot_rod Member Posts: 24,915
    Rinnai shows both their P/S kit or hydraulic sep. as acceptable piping.
    The Grundfos 15-58 should be adequate, per their charts.
    Pay attention to the water spec also.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    hilltown
  • dpenny
    dpenny Member Posts: 12

    All the installation manuals (Rinnai, Navien, Phantom Velocity) say hydraulic sep isn't needed for single zone sys. Just make sure the built-in circulator gives GMP needed given the added extra head from zone.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 17,622

    @dpenny

    What you say is true. But mod cons don't hold much water. Using primary secondary or a LLH with its own circulator makes it certain to have enough flow through the boiler to keep the heat exchanger happy. JMHO.

    hilltown
  • GroundUp
    GroundUp Member Posts: 2,337

    To add to the above comments, "single zone" means nothing. The boiler has a required minimum flow rate and regardless of zone quantity, that flow rate needs to be met. A single zone with 1 GPM when the boiler requires 5 GPM obviously is not acceptable. I'm not a Rinnai person so I don't know what they need, but I have piped a number of other boilers direct with anywhere from 1 to 8 zones as long as the flow rate and BTU output meet the boiler's minimum. In your case, even if the 15-58 doesn't meet the required flow, you may be able to upsize to a 26-99 and hit it. Either way, call Rinnai before you do anything and verify.

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