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fosta-pex v pex al pex: fittings and prep?

archibald tuttlearchibald tuttle Posts: 630Member
I'm about to repipe a house we went early to pex with crimp rings and brass fittings that are slowly degrading and leaking (15 or so years in service, relatively clean but acid water with no chemical treatment). Seeing degradation on both cold and hot water. Seems random. Some fittings look like the day they went in and others have started small leaks and look horrible. Doesn't seem to be related to flex off the fitting or any other configuration issue.

So since we piped this house, we had another house where a squirrel bit through a pex line, and since I'm trying to not have to repipe this house for the 4th time in my life, thought I might try to hedge my bets with a pex-al-pex or pex-al-pe system. mildly more squirrel resistant, although if they nibble off the PE and piss on the pipe maybe the aluminum will corrode but if i'm being given reliable infor by tech types the inner pex layer is itself more or less up to the task in the minor areas that might be so affected.

As best I can tell, once prepped with the chamfer tool (which Viega techs imply peels both the PE and aluminum layer just far enough back for stainless crimp sleeve), Viega specs the same pex press fittings that are used on plain pex. Not 100% clear however that the prep and fitting spec for other, e.g. Uponor/Wirsbo and Bluefin pex-al-pex systems is the same. But not clear that it is not.

The Uponor/Wirsbo multi-press fittings look pretty similar to viega. Assume they use the same prep tool or a prep tool aimed at the same result and the same press tool? To my knowledge there is not a go/no go gauge for the pex press (trade name is pureflow, i believe) standard which is a minor weakness or maybe it can tolerate a broader range of results, or is inherently more accurate in the tooling, but i would think there still could be a go / no go specification. . . .

And then in the NFN department, no one seems to concede, but i believe the prepped Pex-Al-Pex or Pex-Al-PE is suited to F1807 or F2159 connection which follows from Viega saying to use standard pex press fittings which conform to those standards in my understanding.

perplexed in Exeter


  • hot_rodhot_rod Posts: 11,633Member
    If you are looking for 100% squirrel-proof i doubt PAP will be the best option? The very thin AL layer will be no match for the squirrels bite. Copper, maybe even galvanized if you have super aggressive rodents :)

    Viega is the only tube that I know of with an additional layer over a standard pex dimension. So for ANY fitting to fit, the PE and AL needs to strip away.

    Notice the Wirsbo/ Uponor crimp collar is deeper and may not work on Viega.

    My tool, pictured here has been modified to strip back deeper on the tube. This allows me to use compression fittings for panel rads, etc.

    If you search deep enough most all pex manufacturers have a section dealing with compatibility of other brands of rings and fittings.

    Basically if the fitting has the matching standard number it will work and seal. Manufacturers prefer you use their tube and fittings that they have tested and built to their specification.

    I have used standard copper crimp rings on Viega FostaPex for test manifolds or my own home, I'd recommend the Viega fitting.

    Used to be able to buy the Viega stainless cup crimp collars, now they only come with the fitting.

    All the other PAP will be the same OD as standard pex, with the AL layer within the tube.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • archibald tuttlearchibald tuttle Posts: 630Member
    hot rod

    I bought a lifetime supply of the cup crimps when i heard they were not going to be offering them anymore. Well maybe 5 year supply. i'm only a couple bags of a hundred from running out of half inch sleeves. Still got plenty for 3/8, 3/4 and 1".

    i understand that sioux chief makes a compatible sleeve and i can find them listed in their catalogue although i do not find them offered widely by distributors.

    i agree that a squirrel determined to find the chewy core of the tootsie roll could get through the aluminum. i just figured it was an additional deterent as they seem to chew and move on. Just pulled a wire out of a wall that I have no idea why it hadn't shorted and i just happened to finally want to pull a grounded replacement and was in the crawl space and picked it up as a while i'm here kinda thing. squirrels complete removed coating from a bout 6" of both conductors.

    is the aluminum any heavier in the fostapex than the various pex-al-pex offerings. might be a reason to pay the upcharge.



  • hot_rodhot_rod Posts: 11,633Member
    not sure about the aluminum thickness, I think we are talking a few thousands of an inch in either case, one bite .

    With FostaPex, if they did try to chew and the aluminum hurt the fillings in their teeth they might stop and no structural tube damage done :)

    With PAP they would chew 1/2 way thru the tube before they hit aluminum. That would probably be enough to cause the pex under pressure and temperature, to fail.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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