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In joist heating

rebmech Member Posts: 7
In joist heatingI have a customer that is dead set against using the aluminum underfloor tracks for his under floor heating system due to the extra costs. I cannot seem to find some of the pros and cons about this anywhere. I have always used them on other jobs so do not have any hands on knowledge on how well or poorly it works with out them.

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  • Wojo
    Wojo Member Posts: 7
    its all in the insulation

    If you properly insulate the joist cavity with foil face insulation facing the tubing and leave a 2 inch air gap between tubing and foil it will work fine. Oh yeah, also don't forget to insulate the butt ends of the joists. Good Luck, Wojo
  • Brad White
    Brad White Member Posts: 2,398
    In Joist Heating

    It all gets down to conduction vs. your floor assembly and your heating load. The extruded aluminum plates, securely fastened flush to the underside of the sub-floor are superior to all other "from below" approaches. It is more efficient meaning, it will work with lower water temperatures. The pex heats the plate, the plate heats the floor and up she goes.

    Standing back from that, if you suspend tubing in the joist, run fin-tube or some of the other clip-on emitters such as Thermo-Fin, you have to run even higher temperatures. Even with this, you are not heating the floor so much as heating the joist cavity which, in turn, heats the floor. If your heat losses for the room in question are modest, this may be enough, but for most climates, I would think that some supplemental (non-radiant) heating would be needed.

    Of course, insulating your joist cavity below and to the ends is essential, there is no substitute for that "thermal anvil". This applies no matter what type of wood frame application you are considering, of course.

    The ideal RFH system to me is in concrete or gyp-crete, as close to the heated space as is reasonable. A very close second are the half-inch thick insert layers such as Climate Panels or the more expensive but very effective WarmBoard systems. What these have in common is that they are all above the joists and are part of the sub-flooring.  So by this you can see that dropping below the sub-floor puts you at a disadvantage.  Extruded aluminum plates are but one way to restore part of that.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • CMadatMe
    CMadatMe Member Posts: 3,086

    The only time I even thinking about recommending that no plates be used if the radiant is being used as floor warming. Consumers pay for radiant for comfort and comfort is not what they will be getting. Slow response times, uneven heat distribution, and possibly cold floors. Compromise with him and use plates in the areas where they will be spending most of their time.

    There was an error rendering this rich post.

  • Steve Whitbeck
    Steve Whitbeck Member Posts: 669

    with the heat spreader plates you can run lower water temps and thus raise the efficiency of the heat source.
  • hot_rod
    hot_rod Member Posts: 22,261
    do a load calc first

    room by room. Then you will know the btu/ sq. ft required to heat the room. Radiant floors are good up to the mid 20's (btu/sq. ft)

    Floor covering makes a huge difference on radiant floors.

    Conduction is the strongest transfer. Stapling a tube to the floor doesn't provide much contact for conduction.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • rebmech
    rebmech Member Posts: 7

    Thanks to all. I think that i will just present my system the way that i do it, and that will be that. He may have to find someone else to install it the way he wants.
  • Ironman
    Ironman Member Posts: 7,379
    Good Decission

    You can't let the customer design the system and then you be held responsible for it. I wish more contractors would learn this lesson.

    Rehau has thermal imaging of a system with and without the plates. The picture is worth a thousand words.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
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