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Pex Tubing and Spray Foam Insulation

I'm going to be re-installing a heating loop.  In order to do this I'm going to be ripping out the existing ceiling of a garage.  I figure while I'm at it I'm going to hire someone to spray foam the underside to a depth of 3" so I get a nice quiet floor and a vapor barrier.

Is there a problem encapsulating pex (hepex Uponor) in closed-cell spray foam insulation.  I plan on following prudent installation techniques but my concern is a reaction between the tubing and the spray foam. I'd think if its rated for direct contact with concrete there shouldn't be a problem.

What about exansion/contraction? 


  • kcopp
    kcopp Member Posts: 3,717
    the problem is....

    not so much chemical as it is thermal.... the two agents produce a lot of heat. thus it could melt the PEX. It would be best to encapsulate it w/ armaflex first if you are doing baseboard loops or as I did once in a radiant application placed corrugated cardboard directly up under the pex and plates to protect the pipe and create a very small air space. kpc
  • Steve Whitbeck
    Steve Whitbeck Member Posts: 669

    If this is a staple up or even if you are using heat spreader plates you MUST creat a dead air space under the floor and tubing of at least 1 inch. otherwise you will not get the heat output you need.
  • Kenny Greene_2
    Kenny Greene_2 Member Posts: 15
    No air space required

    No air space is required if using aluminum plates. foam has not melted anything in my installations. Foaming an entire house next week that uses Uponor Joist Trak with HEPex tubing.
  • shoudabeenaplumba
    shoudabeenaplumba Member Posts: 74

    I knew about the heat.  I would imagine the skill of the installer would come into play.  If you flash it in layers like you would a cold wall and allow it to cool in between it would be ok, but who's going to check on that?  To pre-insulate the pex with a thin insulate seems very prudent.
  • radmix
    radmix Member Posts: 194
    Heat plates

    When using extruded heat plates you will want to spray the foam directly against the plates. I have been told to check with the different manufactures of the foam to see if it is pex friendly.
  • radmix
    radmix Member Posts: 194
    Heat plates

    When using extruded heat plates you will want to spray the foam directly against the plates. I have been told to check with the different manufactures of the foam to see if it is pex friendly.
  • Steve Whitbeck
    Steve Whitbeck Member Posts: 669

    If you spray the foam directly onto the tubes and plates without an airspace then you loose the heat transfer to the floor that the bare tubing gives off and you also loose the spread of heat over the entire underside of the floor that the airspace creates.

    If it is a tile floor there will be hot spots where the plates are. And cold spots where they are not. Since there isn't any heat under the floor beyond the plates.
  • ChasMan
    ChasMan Member Posts: 459
    What about...

    What about thermal expansion of the tubing? Will the foam not encapsulate it and restrict its movement and thus make it noisy? What about runs of copper that want to move all over the place, whenever it is restricted it tends to move obsticals out of the way with great force and sometimes with a screech and a bang. Would you encase copper in it? Ill be doing a ceiling with copper in it soon and was thinking of wrapping it with some fiberglass insulation prior to foaming it. 
  • hot_rod
    hot_rod Member Posts: 14,785

    I have a handful of jobs installed with foam right against the pex. Radiant Engineering ThermoFins were the plates I used. With a tight grip plate the conduction transfer is moving the energy. I don't think the air space would add much if any with a strong conduction transfer. insulating the pex would limit any loss from the tube and enhance the transfer to the plate,i think.

    Copper in transfer plates will need to move somewhere. Either the copper will move in the plate, or if the fit is tight the plates will try to move. I have seen copper in aluminum transfer plates cause the entire plate to bow when heated. You need to accomodate that expansion movement somewhere. Short runs would help. Expansion loops or expansion couplings like used in baseboards might be needed.

    Reset control and constant circ helps a lot by eliminating wide temperature swing.

    With pex some of the expansion movement is taken up by the tube, like when encased in concrete.

    I still feel a pex aluminum pex is the best match for aluminum transfer plate installs. limited expansion movement and excellent transfer through the aluminum.

    I did an exposed radiant plate job years ago. it was on a metal ceiling in a body shop. i used copper, about 30 foot lengths. i slotted the fins instead of drilling holes. Yes it does move and squeak when it first fires, but we expected that and the owner still likes the ceiling radiant better that the unit blower heaters it replaced. I used pex loops at the ends of the copper runs to allow the movement to be taken up.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • shoudabeenaplumba
    shoudabeenaplumba Member Posts: 74
    This is not a radiant install

    I'm removing some non-barrier pex and replacing with pex with an o2 barrier (hePex).  The system is baseboard and the pex is run under the floor, which is the ceiling of the garage.  My plan was to remove the entire ceiling in the garage to correct some wiring/structural/cosmetic/idiotic problems, and when I do this I was hoping to spray-foam the entire floor, and was wondering if Uponor/Wirsbo hePex was good to go with spraying right over.
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