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Baseboard heating finn size

I have 3/4 copper finn mounted in joist spaces under a floor. The sections have 1 3/4" square finns. Slant Finn rating for finn size of 2 5/8 x 2 1/8 is 580 btu per ft at 180*. Anybody know btu output of smaller finn size copper finn? I can't find any information.


  • Big Ed_4
    Big Ed_4 Member Posts: 2,783
    I would think the output rating was measured with the fin element is its enclosure . The enclosure will increase the convection through the element for more output . Heating plates are a better option for warm floor .
    I have enough experience to know , that I dont know it all
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    The rating in BTIh is directly proportional to the fin area, all else being equal.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,120
    Commonly know as joist bay heating. We have seen it done with bare copper tube, suspended pex tube, UltraFin and most any fin tube.
    I have not seen a fin tube of that dimension. You may find info at the IBR database if it was ever tested and listed.

    As @Big Ed_4 mentioned, without the enclosure the output charts may not be very realistic. Perhaps not much more than bare copper tube if you cannot get convection current movements across the fins.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,828
    These numbers may not be accurate, however I have been told that about 85% of the heat output of Slant Fin baseboard heat is convention and 15% is radiant. When looking at these ratings of 580 BTUh @ 180°F when the room temperature is about 65° to 70°, assumes that the fins are located in the enclosure, and there is a free moving air flow thru the element exiting thru the top of the enclosure. The situation you describe is far from that scenario. There will be minimum air flow across the fins, so the convection currents will also be minimum.

    I believe you would be hard pressed to get 25% of the fin in the enclosure rating from that set up. Based on what is located below the elements (insulation or reflective panels or nothing) the radiant heat will not only heat the floor above the element, it will also heat the people and objects below the element. So if those elements are in the basement ceiling joist, aka: floor joist in the room above the basement, without any covering on the basement ceiling, the basement floor will be receiving a large portion of the infrared radiation from those elements.

    The idea has merit but the amount of heat from those elements will be nowhere near your expectations. You may need to look at a different heat source for that space above the floor.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics