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pex w/ heat tranfer plate vs black onix tubing

J_12 Member Posts: 4
I have a huge space (9000 sq ft on three floors) that will have many zones. the lower level has pex in concrete. the above grade levels will have onix with an aluminum foil 2 inches below with R-30 fiberglass insulation below.

comments please.


  • john_184
    john_184 Member Posts: 2

    i'm looking to put this in my house.i would like to know the pro and con .also looking to avoid any pit fall ,if their any? love to hear your advice!!!!!! thanks

  • extruded plates will outperform regardless of any sales claim to the contrary. I also disagree strongly with relying on reflective insulation to hold up long term, but that's a more controversial claim I will freely admit.

    if your load is low though, not having to trim nails can be nice for a retrofit.
  • Nick_33
    Nick_33 Member Posts: 10

    NRT.Rob ,should i use the reflective insulation along r-13 batt with this installation?one more question for you.could you make up your own tin tranfer plate?

  • I don't recommend people spend money on reflectivity, but it can't hurt. Whether R13 is enough or not depends on whether you are over heated or unheated space. If it's heated below, I would say yes. If not, I would push for R19 to R30 depending on your climate.

    You can make transfer plates, but thin ones don't do a whole lot, and thin homemade ones do even less unless you really do a good job on the tubing groove.

    They are not in the same ballpark as extruded plates though, and they are much more likely to make noise.
  • Nick_33
    Nick_33 Member Posts: 10

    rob, i was thinking of using aluminum coil that you use for siding . tell me what you think.the extruded plates are costly ,do you have to run the plates continuously ,or can they be separated ,if so how much space between each plate...thank you

  • that's not in the same ballpark as extruded plates. If used, I would use PEX-AL-PEX to help with the noise issue, but with that install, the onyx would be a similar level of output.

    extruded plates are pricey, but they do quite a lot for output.
  • Nick_33
    Nick_33 Member Posts: 10

    rob, you've been a great help!!!!!!do you have to run the plates continuously ,or can they be separated ,if so how much space between each plate...thank you

  • ah, sorry. you have to leave a space. I personally let the joist length determine spacing, minimizing cuts or spacing to make cuts at useful lengths to minimize waste. typically no more than 4" or so.
  • jp_2
    jp_2 Member Posts: 1,935
    reflective stuff

    Id like to read up on this.

    infrared light does not act the same as visible light, just as some radar gets reflected by clouds and other radar is not effected by clouds. as the wave length changes so does its properties. I question the real effect of dust, which density is extremely low.

    i like the idea of it because it helps in making an air tight(somewhat) envelope around the tubing.

  • ORNL proved dust will reduce effectiveness very significantly if allowed to accumulate; there is no question about that at all.

    The only question is how much dust will, in fact, accumulate in an upward facing install in a joist bay? I think it's significant. Others disagree.
  • jp_2
    jp_2 Member Posts: 1,935
    Ok, i'll buy that

    so then, the dust must absorb the IR and heat up, i think thats not a bad idea?

    the question then becomes what influence does the foil now have? I would think it would be still more beneficial then detrimental?

    if its detrimental then you have built a heat one-way valve!

  • "more beneficial than detrimental" doesn't say much. That just means it still has some R-value.

    Is it worth spending the money for the apparent R-value of the reflective product, then losing half of it? Would it make more sense to spend that money on real R-value in the first place? Or is the reduced effectiveness plus the air sealing benefits still worth the price? How about, compared to another method of sealing up joists such as rigid foam with spray foam edges? Or spray foam and cardboard?

    Those are the questions that must be answered. Anything is more "beneficial" than "detrimental". You could put a piece of wood in there too, that's more "beneficial" than "detrimental".... but generally we would prefer to see some actual insulation... some real benefit, not just "some". We quantify that benefit with R-value. non-reflective bubble wrap doesn't have much.
  • hot_rod
    hot_rod Member Posts: 22,158
    keep an eye out

    for any high load rooms. Seems you need 160F or more on high load areas. Not a great match is a condensing boiler is being selected.

    I have noticed at high temperatures the tube can give off some odor.

    You could use plates on the areas with high loads. I suggest the extruded plates and PAP Watts Radiant offers for those areas.

    I'm not convinced the foil layer adds a lot for the reasons listed above. It's hard to find foil backed batts anymore, they have as much printing as clean foil...

    The bubble foil products still need a R-19 below them in my opinion.

    My past 4 plate jobs have had foam insulation sprayed right against them. An excellent insulation and means to tighten the rim joist infiltration issues that batts fall short on.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
This discussion has been closed.