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I said "what???"

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heron98105
heron98105 Member Posts: 8
in Radiant Heating

Was at a house this afternoon that is using slant fin 3/4"pipe H1 Element 8' sections mounted under floor between joists for doing radiant heating. There are 2 of these next to each other per 14' X 16" joist cavity with them being offset so that they are covering 12' of the length. They are 3.5" below the 5/4 boards that have Oak HW on top of that, with 1" foil faced insulation 3.5" below the bottom of the units and at the end of the joist cavities. The water is being sent out to them at 135 and they are using 2218's in delta t to return at 120.

The house was built in the mid 30's. I have never seen this before? Has anyone else?

I asked why they just didn't go with Upunor and Joist Trak and received shrugged shoulders as a response.

Comments

  • mattmia2
    mattmia2 Member Posts: 13,449

    People have posted stuff like this here before. It usually doesn't work very well because it has to heat the air then air heats the wood. Radiant heats the wood directly mostly through conduction.

    heron98105
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,895

    Hi, Why did they call you? Is that 15 degree delta working for them? 🤔

    Yours, Larry

    kcoppheron98105
  • heron98105
    heron98105 Member Posts: 8

    I was there working on a different plumbing issue. That was also a little strange in the fact that they had 1/2" run with a 3/4" riser for the second floor guest bedroom bathroom.

  • hot_rod
    hot_rod Member Posts: 25,328

    It is called joist bay heating. Uponor still has a method in their design guide using bare Pex tube in the joist bay. Suspend the tube an inch below the floor.

    IMG_1202.png


    UltraFin is an aluminum convectors that snaps on Pex tube to increase convection. Either these or the fin tube can work fine

    IMG_1199.jpeg IMG_1200.jpeg

    the fin tube is probable even better than these two options for getting the energy from the tube to the joist bay. Generally 140f and higher SWT required

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    mattmia2heron98105GGross
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,763

    Everybody has a better idea that they will experiment with. After they figure out that it may not have been such a good idea, they will still defend it as the best thing since sliced bread! Hard to admit you are an idiot when it sort of works. And if you make emough adjustments, you will get close to comfortable regardless of the operating cost.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    heron98105
  • GroundUp
    GroundUp Member Posts: 2,366

    I have seen this a few times, and tried it out under my tile bathroom floor once upon a time when I had some element leftover from a job. When I was sending 160* water to it, it actually worked pretty well. With that said, the bare PEX feeding it from the mechanical room across the house did a similar job where it passed through below the master bedroom. It's since been switched over to Joist Trak and 105* SWT, which definitely outperforms the BB theory

    heron98105
  • heron98105
    heron98105 Member Posts: 8

    Looks like I am going back again today- I will ask more questions!

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