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pex fasteners

Risktakr2 Member Posts: 1
I am building my own home and intend to attach pex to the bottom of the floors for radiant heat. i am not using heat transfer plates but intend to fasten the pex directly to the floor and then spray foam the floor to seal in the heat as it transfers up. 2 questions..1. your thoughts on my plan...2. is there a fast method of attaching the pex ,such as staples?


  • Adk1guy
    Adk1guy Member Posts: 66
    edited April 2023
    I think you should read the manufactures handbook and follow a design they recommend. Last I knew what you propose is called staple up which is obsolete because you need high water temps because the heat doesn't transmit and spread. The high temps don't let a mod con boiler run efficiently. And staple up requires air space at least the thickness of the pipe. Last time I put in staple up was in the days or the orange rubber hose disaster which transitioned into black rubber with a O2 barrier, and the wholesaler rented a staple gun to me. I would recommend and use heat transfer plates. II have plans to pull down my orange rubber staple up where accessible in my own home put in heat transfer plates and i will put fiberglass insulation underneath. I imagine wallies with more current training and experience will chime in.
  • TonKa
    TonKa Member Posts: 104
    edited April 2023
    Why bother with foam? It's your most expensive choice for for an application which doesn't need it. I also think there is a chance the foam will expand and wrap the pex, causing it to be isolated from the floor between staples.

    Yes, there are staples for this. Your method is literally called "staple up".

    Also, reconsider your choice of no heat transfer plates.
  • ethicalpaul
    ethicalpaul Member Posts: 5,757
    I think your idea that heat will efficiently transfer from a length of pex in close proximity to your floor is wildly misguided.

    Free advice, use these: https://www.supplyhouse.com/Uponor-Wirsbo-A5080500-Wirsbo-Joist-Trak-1-2-Heat-Transfer-Panel
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • HomerJSmith
    HomerJSmith Member Posts: 2,477
    edited April 2023
    The mistake is assuming that the tubing is the heat emitter. Somehow you have to extract the heat energy from the tube. Even fin tube baseboard has... well... fins to extract the heat energy. The extraction area of the tube is very small which is why you need to expand the area which is why one uses transfer plates in underfloor. Even radiant floors cast in concrete, the tube isn't the heat emitter, the concrete is the heat emitter. Are you getting the picture, here?
    Spray foaming staple up tubes without transfer plates is the worse thing you could possibly do. It would make correcting a mistake almost impossible to fix. You don't need foam to prevent backloss. Regular insulation works just fine.
    Also, with your scenario, the Delta-T back to the boiler would be narrower than a tight-rope in a circus. Also, you'd be wondering why your house doesn't heat up. BAD IDEA!

    Experience is what you get when thing don't go the way you planned.
  • MaxMercy
    MaxMercy Member Posts: 514
    I just don't like PEX for heating and PEX doesn't transfer its heat like copper does. Since PEX doesn't like to give up its heat I would definitely use transfer plates.

    I don't know if even using transfer plates would allow for a low temp boiler, which may be a problem in the future if laws affect high temp boilers (honestly, who knows?)
  • Alan (California Radiant) Forbes
    I've seen bare PEX tubing work here where it's relatively warm and in those structures that have good insulation and double glazed windows. I once asked someone at Uponor if they had any engineering information about bare PEX staple-up and they said they do not recommend that type of installation.

    Do yourself a favor and just do it once - the right way. Use plates (2 runs per bay) or Ultra-Fin (one run per bay), do your room-by-room heatloss calculations and with that information, follow the instructions of whatever product you chose.

    A customer had me come to his house a couple of weeks ago to help him figure out why the heating system he installed was not heating the house properly. He used plates, but only one run per bay. I asked him if he read the instructions, but I didn't need an answer.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • hot_rod
    hot_rod Member Posts: 22,353
    I did a few installations with Ultra Fin, I ran two tubes per bay, staggered the fins. It is sometimes easier to pull two tubes in a bay with the "sewing" method.

    Yes the spray foam will get between the tube and floor and push it away and insulate it away from the floor, not a good idea. It will do the same with transfer plates to some extent.

    Any idea what the heat load is? I'd say 10- 15 btu/ ft with a bare tube staple up. Suspended tube, bare tube staple up, and UF can all work satisfactorily if the loads are low enough.

    Consider plates or Ultra Fin.

    If you must, here is the clip to use for hand nailing.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream