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Viega FostaPex and compression style fittings

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hot_rod
hot_rod Member Posts: 22,254
I have been using then Caleffi Universal pex fitting with Viega Fostapex successfully for about 8 years now.

You need to strip back the outer layer far enough for the blue, segmented compression ferrule to slide over the tube and have a small amount of tube protruding.

A slight modification to the Viega strip tool allows this to work. I removed the blade and drilled another hole, sliding the blade forward to allow the blade to strip the aluminum layer about 3mm deeper.

Unique about the Caleffi pex fitting is the insert brass that goes inside the tube has a double o-ring seal and a slight taper, so it slides inside the tube tightly and corrects any ID out of tolerance, or slightly ovaled tube.

Also a flat, captive, composite washer inside the insert prevents electrolysis, where the aluminum layer could contact the brass insert fitting if PAP tube with then internal aluminum layer is used.

The outer seal, to the manifold port is made with both a "nose" o-ring and brass taper.

Invest in the "flare nut" style box wrench which allows you to tighten them onto the tightly spaced manifold ports without marking up the brass nut, or filling the air with colorful language often heard when using a slip joint pliers.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
TinmanSWEIBoon

Comments

  • bob eck
    bob eck Member Posts: 930
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    Hot rod are you using the Caleffi compression fittings on the Caleffi radiant manifolds?
  • hot_rod
    hot_rod Member Posts: 22,254
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    Yes I am.

    The thread on most manifold ports are common and standard. But the tapered end that inserts into the manifold port varies from brand to brand. We have found some other brands of manifolds that our fitting will work with.
    Many radiant and tube manufacturers shop around for manifolds, so they tend to change from time to time.

    The same on then top end, that actuator thread is common to many manifolds, but the actual pin height and stroke may vary. So even if the actuator screws on, you need to confirm it allows the valve to open and close fully.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Boon
    Boon Member Posts: 260
    edited August 2016
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    This post is a lifesaver. I want to use the Caleffi manifolds and I already bought the fostapex.

    Can I swap the position of the air separator & drain on the 668S1, which would allow me to flip the manifold over & turn it around; I need the piping to go up into the ceiling - not into the floor.
    DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.
  • Boon
    Boon Member Posts: 260
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    @hot rod is there any reason I can't use the Caleffi 682540A 1/2" PEX-AL-PEX Loop Fitting for Manifolds with Fostapex on my 6686I5S1A manifolds?

    I'm guessing I can't use the 682540A with fostapex since you posted this workaround for the other compressions fittings. Wanted to double-check before I release too much colorful language (x18 fittings) into the atmosphere. Thanks
    DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.
  • hot_rod
    hot_rod Member Posts: 22,254
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    FostaPex has a larger outside diameter than any pex due to the aluminum layer and PE coating. If you strip that off, you end up with a standard pex OD, 5/8". The Viega crimp fittings require you to strip back that jacket also.

    I have both 1/2 & 3/4 FP on my Caleffi manifold, it takes some massaging to make it work.

    The standard Caleffi pex fitting works fine, the only difference between the PAB fitting is it has a brass ferrule to clamp down on PAP, which has an aluminum layer inside, much stiffer tube.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Boon
  • Alan (California Radiant) Forbes
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    Looks great, Hot Rod. One of my customers is interested in running FostaPEX using your method, but I called Viega and they said FostaPEX is designed to be used with PEXPress fittings only and there is no way they would warranty the installation, especially after modifying their tool. I'm sure the Caleffi fitting is bulletproof, but I just get a little nervous when the manufacturer disavows responsibility. My pockets aren't that deep.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • hot_rod
    hot_rod Member Posts: 22,254
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    Looks great, Hot Rod. One of my customers is interested in running FostaPEX using your method, but I called Viega and they said FostaPEX is designed to be used with PEXPress fittings only and there is no way they would warranty the installation, especially after modifying their tool. I'm sure the Caleffi fitting is bulletproof, but I just get a little nervous when the manufacturer disavows responsibility. My pockets aren't that deep.

    As expected :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • BobC
    BobC Member Posts: 5,479
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    Corporate CYA raises it's head once again.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge