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Onix for staple-up

Glenn Sossin_2
Glenn Sossin_2 Member Posts: 592
I agree with your thoughts, but its the rate of tranfer thats in question here. The amount of heat energy that leaves the pex is primarily limited by the surface area in contact with the sub-floor. The amount of heat energy transferred to the joist bay is minimal. Air is not a good medium for transference of heat energy.

Think of a piece of baseboard and what is done to draw the energy out of the copper. We place hundreds of fins on a 10ft piece to increase the heated surface area to heat the air.

The rate of heat transference is also a function of the difference between the temperature of the two mediums. If the pex is heated to 140 and the joist space is already at 120, how much heat energy is going to be transferred ?

A 3/4" piece of copper at 150F will only release 30 btu's of heat per foot to surrounding 70f air. See the attachment. How much could the pex possibly release? I'm sure this info is somewhere - will try to find it.

Comments

  • Brian
    Brian Member Posts: 285
    Onix for staple-up

    I had someone tell me that you can get the same performance from Onix as you would with standard pex with plates.Does anyone have any experience with this or opinions.

    Thanks,
    Dobber
  • hr
    hr Member Posts: 6,106
    define performance

    The goal of warming a space with radiant is to get the energy from the fluid stream to the floor and into the space to be heated.

    At every step you have efficiency choices. A high efficiency boiler will transfer the energy from the fire to the fluid more efficiently than a low efficiency boiler.

    A smart high efficiency circ will move the fluid with less energy consumption.

    A good conductor will transfer the energy in the fluid stream to the floor more efficiently. Hard to beat pex in an aluminum subfloor or extruded plate for optimum performance.

    I've done a fair share of rubber staple ups. They can and do heat the space when designed and installered (insulated) properly. They do require a higher fluid temperature, sometimes much higher depending on the load.

    Looking at the cost difference these days, you get a lot more transfer efficiency with the extruded plates for not much, if any, more $$s.

    Watts Radiant, as you know offers both systems and also PAP tube for a nice quiet hi performing under floor system.

    hot rod

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  • Leo G_99
    Leo G_99 Member Posts: 223
    Dobber

    I had my watts rep ask his technical people. Their answer was that it was only about 4-6% less effecient, and they did not recommend plates.

    If you go to the website and view the pertinent info, you will see that they want quite a few staples, i.e. very little room between them, and they want the stapler set to slightly "squish" the tubing. This is to get a better surface contact.

    The big job that I used Onyx on, I felt that even if it was only 6% more effecient, I felt better using a plate. Hard to find one that fit their 3/8 tube, as its' outside diameter is more then 1/2" pex. But I did find one, and installed with plates.

    We had a very cold couple of weeks in December, about 6 degrees colder then our "average" coldest day, and never heard a thing from this client. As the old saying goes, "no noose is good noose!"

    Leo G
  • ALH_4
    ALH_4 Member Posts: 1,790
    Watts Plates

    What do they mean by 4-6% less efficient? Are they talking about boiler efficiency? Do they mean plates increase the output by 6%? From past experience, I know the output of plates beats staple-up by more than 6%. Ironically, Watts also sells extruded aluminum plates for pex, but not for Onix.

    Onix has the primary benefit of being easy to work with. The thermal conductivity of EPDM is not good, and the wall is much thicker than pex. For cost reasons, I believe there will never be a plate for Onix, so I think they will stick with a "Look Ma, No Plates!" marketing strategy as Onix is much more important than extruded plates are to Watts.
  • Steve Garson_2
    Steve Garson_2 Member Posts: 712


    I have Onix tubing for my radiant. As said, it needs a higher temp. Heating my hardwood floors requires 145* water to reach a 85* floor temp. Otherwise it works fine. In the poured concrete it doesn't need the high temp. My guess is that my contractor used it because that's what his supplier suggested. In retrospect, he had little experience with radiant and we have to make some fixes on our own after the project was done.
    Steve from Denver, CO
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Don't think so.

    Plates draw off the heat energy from the tube and transfer that energy directly to the medium they are in contact with. The denser the medium, the higher the heat transfer. Wood being a denser mass than air, the overwhelming majority of heat energy is transferred to the sub-floor.

    The Onix, if I understand this right, based on the web site data sheet, is simply stapled to the underside of the sub-floor. There is minimal contact between the tube and the floor based on their installation method -therefore, minimal energy transferred by conduction to the sub-floor. The balance of the heat energy therefore must be released to to air in the joist cavity, and reflected upwards with the foil faced insulation.

    I just find it hard to accept that this hot air will transfer more heat energy through the joist air than the plates in direct contact with the floor.

    If have a drywall bucket filled with 130F hot air and I toss it on you, do I get any reaction? Not much of one. Now, I take that same bucket, fill it with 130F water and toss that on you. Quite a difference.

    The point is, air has little mass and can't hold/transmit heat energy very well. Thats why you have to move several hundered cubic feet a minute to heat a room in a forced hot air system. Theres a minimal convection effect in the joist bay. I wonder just how much heat energy is really being transfered by the air in the cavity to the sub-floor versus transfer plates.

    I suppose if you increased the temperature of the water going through the onix tube, that would increase the joist bay temperature to help increase the heat transfer. Trade off there is your running your system at a higher temperature - less efficient scenario.

    If you wanted to do your installation this way, there was a company called Ultra-Fin. Don't know if they are still around. They basically clamped a louvered plate onto the pex to create air movement - hence faster heat exchange.

    For the record, I wouldn't use this either. I think plates are the best method for underfloor joist heating.
  • Troy_3
    Troy_3 Member Posts: 479
    Pictures

    Hotrod: Please explain the photos. What is the method of installation in each photo. A picture is worth a thousand words-only if you know what it represents. Thanx troy
  • hr
    hr Member Posts: 6,106
    good point, Troy

    one is Onix stapled to the bottom of 3/4 Advantech. Insualted with a 6" batt with aluminum foil (from my kitchen) installed on the batt. Air space as per manufactures spec, as well as staple space.

    The other is 1/2 pex in ThermoFin lite plates, under the same Advantech. Same insulation thickness, without the aluminum foil.

    Same loop length, same supply temperature, and same flow rate set with manifold flow gauge. Also same run time.

    The camera shows the more powerful transfer with the plates as well as a better spread.

    hot rod

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  • Mike Thomas_2
    Mike Thomas_2 Member Posts: 109
    simple physics

    I think many good points were made in previous posts. I think one point has been overlooked. Once the heat energy is in the joist area it will go somewhere. It is called the law of energy conservation. The law basically says that energy can neither be created nor destroyed, it just changes form. Once you move that energy, aka heat, in to the joist area it doesn't just disappear. It goes somewhere. With insulation you are encouraging it to go somewhere that you want it to go, the floor. With plates you might get it to go to the floor faster, but without plates the energy is still there, it just might take a little longer for it to transfer to the floor. Because you have to run Onix at a higher temperature just means that you are probably transferring heat at a slower rate and some of it is escaping before it can be transferred to the floor. Maybe a better method of insulation is the real answer. The heat is there, you just have to get it to go where you want it.
  • hr
    hr Member Posts: 6,106
    I've also tried copper in extruded plates

    and the transfer between that and pex is a thing to behold.

    By the time you could walk to the far end of the loop the plates were warm.

    The transfer ability of a good conductor (copper) to a good transfer plate (extruded aluminum) makes a difference in the performance of the emitter.

    I can actually grab and hold a piece of Onix with 150F flowing thru it. Now try that with copper.

    The other thing to notice is the delta t (beguinning of the loop to the end of the loop)of the two different method.

    If the fluid returns at the same, or near same temperature, guess what...

    Here is an interesting pic I took in my IF tests. That's a piece of Warmboard with a couple grooves routered in between. Notice what the break in the aluminum surface has done to the heat transfer!

    hot rod

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  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592


    Hot Rod

    Love those pictures. Dare I ask what kind of camera did you use? Is it within the budget of us people that don't on hotrods? I've got to put that on my wish list this year. My wife lets me buy anytools I want - the catch I have to fix what ever it is that goes wrong. I like that deal.

    Can I have your permission to reprint and show these pics to my customers? I assume that would be ok becuase this is a public forum - just want to be sure. I'll give you credit - well deserved. Only a truly dedictate heating specialist would go to those measures. Hats off to you. You clearly have a passion for this, as do I. Thats why I want to buy a camera like that too.

    Agree with your point about the delta T in the Onix tube. I'll bet it's minimal which would mean minimal heat tranfer. I beleive the key concept here is - heating the joist air with this tubing does not equate with heating the floor above.

  • hr
    hr Member Posts: 6,106
    Entry lever IR cameras

    are in the 12- $15,000 range. I saw a bunch of different brands at the AHR show this spring.

    The Flir brand camera I used in those pictures belongs to City Utilities in Springfield. With all the extra lens, etc it ran about 75 grand!

    Credit the RPA (Radiant Panel Association)when you use those pics, some of them were sponsored by the association.

    My goal, and that of most of the contractors on the "green movement" is to install the most efficient systems in any phase of construction.

    For my piece of that puzzle my goal is to heat the space with the lowest possible supply temperature. Which, of course, plays nicely to mod con equipment, and the most efficient emitter.

    I'd put Warmboard at the very top of that list, extruded plates a close second place.

    And the thickness of the aluminum does matter. Foil tape doesn't move heat as well as an extruded plate.

    hot rod

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  • jp_2
    jp_2 Member Posts: 1,935
    4-6% not true

    Hot Rods pictures clearly show more than a 6% increase in conduction between staple up and the plates, just look at the pictures.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Out of my range

    Hot Rod

    I guess this will be on my wish list for quite sometime. This seems like such a useful tool and takes any questions out about what is really going on.

    Any pics like this of a snowmelt installation ??

    Thanks

    Glenn
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Pics - can't argue with that

    As some wiseman once said? picture is worth a thousand words
  • Steve Garson_2
    Steve Garson_2 Member Posts: 712


    As a homeowner with Onix tubing, this thread is interesting. My delta-T at the boiler is 20* with a boiler temp of 145* heating 3/4-inch plywood and 3/4-inch Oak flooring.

    While there are the obvious inefficiencies from running the higher temp, what temp would I need to heat that much wood with PEX and plates? If the delta-T is 20*, for both technologies, doesn't that mean it's the same BTU in and BTU out?
    Steve from Denver, CO
  • ALH_4
    ALH_4 Member Posts: 1,790
    Plates & Onix

    Onix works.

    The same delta-T means the same output but only if both are running at the same flow rate.

    However, the supply temperature can be 100°F at design with extruded plates. I have seen sub-100°F temperatures heat a home to 68°F when it was 24°F below zero.

    The response time of the system will be better with pex and plates. Constant circulation evens this out some, but only if the zone is truly circulated continuously on outdoor/indoor reset.
  • hr
    hr Member Posts: 6,106
    plenty of data out there

    www.radiantengineering.com has boat loads of output data on the ThermoFin extruded aluminum transfer plate product. This seems to be the most common transfer plate out there. It's sold under the Watts Radiant, Viega, Roth, Slant Fin, and other names, if I'm not mistaken.

    ASHRAE and the RPA funded a research project at KSU a number of years ago.

    "Develop a simplified method for determining heat transfer design impacts associated with common installation alternatives for radiant condiut"
    that's a mouthful :) I believe this study is available from the RPA or ASHRAE. ASHRAE Research Project 1036 June 22, 2002

    One conclusion of that study
    "The use of heat transfer plates dramatically increased the heat flux emitted from a radiant panel by better distributing the thermal load to the radiant surfaces"

    Also graph 15 on page 28 of that study "Hydronic Ramp Up Time" shows plates at 3.89 hours and no plate staple up at 10.05 hours.


    The same applies to contractors stapling pex or PAP directly to the subfloor without transfer plates, by the way. It's not just an EPDM issue, it's the method of attachment in question, regardless of the product type or brand.

    Some suggest limiting direct tube staple up output to 15 btu/ sq ft or less loads.

    hot rod

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  • john_83
    john_83 Member Posts: 76


    I've installed all pex with plates onyx and recently two jobs with warm baord but mostly onyx by the boatloads and not that im disagreeing with you guys but the only time i've had problems with onyx is with large rooms with high ceilings and alot of glass. my design temps are usaully about 110-140. The 140 degree temp s typically in the lare rooms that i spoke about. other than that i get by with 110 to 120 degree supply water no problem i guess it all depends on install and the key is insulation i suggest being around when its being done. Never really liked the whole idea of pex with plates more of a pain on install. Now warm board on the other hand if i could get more people to install it i would install it on every job i could. But its a very costly to install on paper but it all evens out in the end. The other problem is selling the general contractor on installing it.
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