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Radiant - mixing vs. injection

hr Member Posts: 6,106
Is this a GV Gold boiler by chance? Those have factory installed vs mixing under the hood. They first had 3 way thermostatics but both Weil and Burnham use VS mix now. that tells you something :)

A GV Gold could accept radiant tempersatures without additional mixing controls, generally.

Too late to go with a mod con? Much better boiler for low temperature emitter systems. Brings modulation, od reset, and eliminates the need for combustion air vents into the space. All add up to increased savings and comfort.

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  • Boston
    Boston Member Posts: 71
    Radiant - injection vs. mixing

    Can anyone comment on the reason to use injection vs. mixing in radiant floor heating applications?

    Will be constant circulation - viega. Climate panel application.

    I see how both would work just fine. Boiler is non-modulating W-M Gold series.

    Any thoughts would be really appreciated.
  • Brad White_102
    Brad White_102 Member Posts: 8
    I have used both

    and in all sizes of systems, but I would have to say that injection I would reserve for larger systems unless the temperature difference primary to secondary was narrow.

    Yes, there are small residential size systems that use injection (and I can get excited about that!)

    My concern in a small system drawing higher temperature water would be the primary GPM required. Say 180 F. primary mixing down to say, 100 F. secondary, would need very little primary flow.

    But if you need only a small amount of primary to meet your secondary setpoint, how low a pump selection, let alone turndown, can you get? Or you are in the range of on-off control with associated equipment cycle-wear.

    If too small a flow or load and you run off of a VFD, how low can a pump go before it cycles off? I do understand that there is no real limit to turndown (someone posted that once; have no corroboration). But at some point you get into the cycling range I would think, in a small system.

    On larger systems or where the P-S delta-T is narrow (say 120 F primary mixing down to 100 secondary) and if a larger volume for steadier control, I can see injection pumping.

    Otherwise, a mixing valve (3-way on Mod-Cons and 4-way on conventional boilers) gives smooth steady control across a wide variety of systems.

    Not against injection, but that third circulator parasitic loss sometimes bugs me. Probably not a fully justified concern but something I think about.

    My $0.02 and I will sit back and see what others have to say!


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