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3/8\" pex

Harvey_2 Member Posts: 27
how many btu's can 3/8" pex move at a 20 deg delta T?


  • hot_rod
    hot_rod Member Posts: 19,968

    at 180F?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Mike East
    Mike East Member Posts: 13
    3/8\" Pex

    BTU output is dependent on several variables, fluid temp, type of fluid, flow rates, and installation method. To give you a snap shot of performance with fixed variables review the following chart to see the BTU output of various installation methods. This data comes from an independent study from Virginia Tech.


    BTU Output with 110°F Input Water Temperature

    10 Joist Space, aluminum louvers in air cavities, 24" spacing (Ultra-Fin)
    5.6 BTU/hr-ft2 Output

    9 Joist Space, no heat transfer plates, 8" spacing
    7 BTU/hr-ft2 Output

    8 Structural plywood with aluminum facing, 12" spacing (WarmBoard)
    17.5 BTU/hr-ft2 Output

    7 Thin plywood with aluminum backing, 7" spacing (Quik-Trak)
    18 BTU/hr-ft2 Output

    6 Joist Space with heavy gauge extruded aluminum plates, 8" spacing (Thin-Fin)
    18 BTU/hr-ft2 Output

    5 Gypsum cement overpour 1 1/2" thick, 8" spacing
    18.5 BTU/hr-ft2 Output

    4 Expanded PS base with aluminum plates, 6" spacing (Roth)
    19.1 BTU/hr-ft2 Output

    3 MDF board with foil face, 8" spacing (ThermalBoard)
    19.5 BTU/hr-ft2 Output

    2 RAUPANEL 8" spacing
    28 BTU/hr-ft2 Output

    1 RAUPANEL 6" spacing
    30 BTU/hr-ft2 Output
  • hot_rod
    hot_rod Member Posts: 19,968
    really the output of any radiant panel

    has to do with the delta t between the floor surface temperature, and the temperature of the room. Rule of thumb 2 btu/ square foot per degree difference.

    So an 82 degree radiant surface in a 68f space would give you 28 BTU/ square foot output.

    Some of the installation methods are more efficient getting the energy from the fluid stream to the panel. typically the aluminum transfer plates or with soild aluminum surfaces will be the best conduction transfer and best performers at the lowest possible supply temperatures.

    Beware of the 40- 50 btu/ square foot output claims, as the formula above shows you :)

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