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Questions: 120-degree supply water when mixing panel radiators with in-floor radiant

Steve Zerby
Steve Zerby Member Posts: 3
edited July 2018 in Radiant Heating
I am designing several rooms for 120-degree water supply so that I can use an air-to-water heat pump for my supply water in the future (though for the time being I will be mixing down from my old 180-degree boiler).

In several rooms I cannot get enough BTUs out of an infloor-system alone, even at 6" spacing, and want to supplement with a euro panel radiator in each of two rooms make up the approximately 1800 BTU per room shortfall. I see no output charts for euro panels that go below 140-degree supply water temps.

A couple of questions:

• Is a 50% reduction in BTU output a reasonable assumption for dropping supply temp from 140 to 120 with the panel radiators?

• What is the best way to incorporate the panel into the radiant-loop piping? Flooring loops will be in the neighborhood of 275 feet. There will be two radiators (one each in two rooms on the same zone). The round trip through the two panel rads will be about 140 lf. And for the radiator loop should I pipe it diverter T? two-pipe? I've talked briefly with a couple of my heating subs and the recommendation is to run the panel radiators off their own loop but still on the same manifold as the flooring loops, and balance it with flow-control valves.


  • hot_rod
    hot_rod Member Posts: 21,804
    Good for you designing around a low SWT.

    There is a derate formula pages 55 & 56 for panel rads in Idronics 12.

    A manifold piping is a great option, TRVs on the panels page 72 & 73 for example.

    But read he entire issue for other tips.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SuperJ
    SuperJ Member Posts: 609
    At low temps you definitely want the rads piped in parallel to avoid diluting the SWT. Home run to a manifold might be the best case way to pipe, but you can get more creative if you need to. You could also run a single supply and return the room and branch out between the rads (parallel). Many manifolds and panel rads have built in balancing adjustments. I would put a TRV on each rad to micro-zone it, and simplify the integration with the infloor heat.
  • hot_rod
    hot_rod Member Posts: 21,804
    as Super said.. It's nice to pipe the rads separate as in the shoulder season it nice to just fire the panels, quick and easy to warm a room. You can also fine setback-able TRVs nowadays.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 7,542
    I like the look and low profile design that Runtal offers. I have used the to do exactly what you suggest. Run them under your larger windows to offset the heat loss. Here is the derate data http://runtalnorthamerica.com/bisque/calculating_btuh.html
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Rich_49
    Rich_49 Member Posts: 2,766
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833