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PEX install under floor options...

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Bultar
Bultar Member Posts: 8
in Radiant Heating
A few questions about retrofit PEX install. I have thousands of nails protruding through the floor about an inch or so. I plan to install PEX just below that level, attached to sides of the joists to avoid all the nails. Then insulate below before putting up basement ceiling.

1. To avoid noise of expanding PEX squeaking against joists, I'm thinking of using stand-off clips with a criss-cross pattern of PEX (see pic for example. Those are Talon clamps just for the pic)) - does that make sense? PEX will not touch subfloor or joists.

2. And how careful to I have to be about scratching the PEX when pulling past all those nails? Are very minor surface scratches on the PEX ok? (Is the O2 Barrier a layer/coating on the outside of the tubing that can be easily damaged?)

3. I've read pros and cons of using a layer of foil-bubble insulation, some say just a fiberglass batt layer is just as good... any recommendations?

Thanks!

Comments

  • Gordan
    Gordan Member Posts: 891
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    That will by no means be a low temp system

    Any expansion issues will be exacerbated by the wide temperature swings. Also, leaving those nails sticking there - are you absolutely sure that none of your pex will expand upward and, over the years, rub on those nails? The kind of system that picture shows will not be good for very much heat output - I hope you've done your homework and your calculations before embarking on an expensive exercise in frustration.



    There's a product called Ultrafin that might help with heat transfer, if you're dead set on suspended tube. But nothing will do as well with temperatures as low as you'd get by using extruded aluminum heat transfer plates. You should also look into using pex-al-pex, which should limit expansion-related issues - its thermal expansion is 1/9 of pex.
  • Bultar
    Bultar Member Posts: 8
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    explain...

    Why do you say it will not be a low temp system?

    What do you mean by "the kind of system" shown? What assumptions are you making?

    The back and forth "offset" run of the PEX is one option manufacturer suggests to account for expansion (along with loops), and it keeps tubing completely off of joists, so no squeaking from slightest movement.

    Yes, I've done tons of homework... I've read many places about complaints about noisy transfer plates, and successful installs of just suspended tubing in closed/insulated joist bays.

    Any input from pros out there?

    Thanks!
  • Gordy
    Gordy Member Posts: 9,546
    edited January 2011
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    Low temp radiant

    Is when you use plates in a sandwich type install, or poured in concrete or gypcrete. These methods of application allow you to run water temps below say 120* depending on your load.



    With under floor there are different categories.  Staple up with plates, staple up, and suspended tube. You are falling under suspended tube with your installation idea.  You could use water temps as high as 160* depending on your heat load.  If you are looking to just do floor warming might be all right. You would be lucky to squeak 20btus sf out of it. That depends on youyr floor coverings as with any RFH application.





     The difference is fuel consumption, comfort, and noise. Plates when installed correctly with the right type of tubing, and control strategy are not noisy.



    Gordon
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
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    never do this

    or any radiant system without a room by room heat load calculation. a real one, that looks at R-values, no magic "energy factors" or voodoo like that.



    Especially with an extremely weak radiant method like naked staple up or suspended tube, you have to be careful. with a wood floor you're really limited to about 15 BTU/sq ft at "hot" water temperatures and 20 at "why are you doing radiant anyway" temps (180 or so). Not strong, not low temp.



    At extremely low output requirements the method works very well, but there are many, many failed and underperforming naked stapleup systems out there because someone didn't run the numbers and threw the dice.



    Noisy plates are a sign of poor system design or installation as well. leaving room for expansion at the loop ends, reset control, heavy plates, and/or PAP tubing can all help.



    no idea what your situation is but it's at least 75% likely your best bet is a grinder with a cutting wheel, or to do a hybrid radiant/radiator or radiant/baseboard system if you must go suspended tube.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Gordan
    Gordan Member Posts: 891
    edited January 2011
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    Never mind...

    I guess too much coffee makes me see things.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
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    ?

    I didn't think his post was particularly unpleasant?
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Bultar
    Bultar Member Posts: 8
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    thanks for info

    Thanks for the info.



    FYI, a little on my situation... in eastern PA, avg low temp in coldest month is about 20F. Ranch brick house built in '55, little under 1700 sf. Now have about 150' of baseboard (looks like Slant/Fin). Quietside QVM9 boiler replaced an old oil boiler couple of years ago (with intent to eventually replace baseboard with underfloor radiant... mostly because I need to move some walls for renovations, and to eliminate the very annoying "ticking" in baseboard heat). Already replaced all windows in the house, and will add more insulation as I complete rest of remodel, to reduce heat loss.

    Considering a pellet stove insert in the main living space, as an alternative heat source, and so we can have the ambiance of a fire in the fireplace without the horribly inefficient old fireplace.



    And still considering other options...

    - like leaving some high-temp baseboard around outer walls in LR/DR areas (I'm not moving those walls, and not so worried about the noise there),

    - maybe using something like ultra-fin,

    - I still might go ahead with the huge PitA of grinding those 6000 nails... so I could use heat transfer plates.



    A few questions:

    1. If I use snap-in extruded plates, do I need to grind the nails to completely eliminate the sharp edge of nails? Or can I get away with easier sawzall "almost flush" cutting of nails that leaves a tiny bit of a sharp edge exposed?



    2. If using plates, how do you deal with joist bracing? I have a little bit of solid blocking that I'll have to drill or remove, but mostly cross-bracing (as in the pic), that I think I can just pull PEX between brace and subfloor and have a bit of gap in plates.



    3. And one of my original questions - how delicate is the PEX regarding scratches? Is the oxygen barrier a coating/layer on the outside surface of the PEX that is easily breached? (like minor scratches stray nail, etc., or from pulling through holes in joists, do I have to use butterfly clamps or similar through all holes in joists?) PEX manufacturer (Everhot) documentation just says "don't scratch".



    Thanks!
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
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    if the aesthetics don't bother you

    the most economical route to comfort and low temps is to keep your baseboard, but re-loop it, and run plateless tubing in the joists. would be the easiest install too.



    if you want to get rid of the baseboard you're probably gonna want the real deal with the plates. those plates need to have direct contact to the subfloor, no "nail points" allowed.



    pex isn't that fragile. Use a pipe that doesn't have the o2 barrier on the outside and there is no real big deal as long as the penetration can't really "get in there".



    you just don't plate the cross braces. Hope that helps,
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • CMadatMe
    CMadatMe Member Posts: 3,086
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    I have to Agree

    With both Gordan and Rob. You looking for trouble here. Rob provided you the key to a proper installation. The heat loss and from there a proper design.



    I would never and mean never recommend the non use of heat transfer plates in a heating situation. If floor warming as the guys said then maybe but I would make sure I used floor sensors and have some means of keep the floor from having huge response times. You see more of what we call "catching the night" in non plate applications. A dead cold floor during the day due to solar gain and day time temps struggles to keep up with the night.



    My questions is how are you controlling the radiant? Is outdoor reset in play here?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Bultar
    Bultar Member Posts: 8
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    partly aesthetics...

    for the multiple reasons, we're going to get rid of all (most) of the baseboard.



    I have the PEX already, with O2 barrier. Don't I need that? (Or should I just switch to S/S pump and not worry about it?)



    thanks again,

    Bryan
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
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    I mean

    some pipes put the o2 barrier not on the outer layer.



    a few scratches in an o2 barrier won't kill your system anyway.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Gordy
    Gordy Member Posts: 9,546
    edited January 2011
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    Lack of baseboard

     The thing is you are removing some of your baseboard. So now those rooms are completely dependent on the radiant heat installed.



     If you have not done so you need a room by room heatloss done to know what kind of heatloss you must compensate for, and see if the radiant can do it on its own. Other wise supplemental heat would be needed if it can not. Such as panel rads, or baseboard, as already mentioned by Rob.



     Question if you are moving walls, and renovating anyway why not consider a sandwich type install?   It would save you cutting off 6000 nails, and weaving pex inside of joist bays over your head. You would still need to insulate.  A sandwich install with plates would give you more output. Thus eliminating the baseboard.....depending on your load.



    Gordy
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